Acetylene, The Principles Of Its Generation And Use
F. H. Leeds and W. J. Atkinson Butterfield

Part 7 out of 9

or oxy-coal-gas blowpipe.



Now that atmospheric or Bunsen burners for the consumption of acetylene
for use in lighting by the incandescent system and in heating have been
so much improved that they seem to be within measurable reach of a state
of perfection, there appears to be but little use at the present time for
a modified or diluted acetylene which formerly seemed likely to be
valuable for heating and certain other purposes. Nevertheless, the facts
relating to this so-called carburetted acetylene are in no way traversed
by its failure to establish itself as an active competitor with simple
acetylene for heating purposes, and since it is conceivable that the
advantages which from the theoretical standpoint the carburetted gas
undoubtedly possesses in certain directions may ultimately lead to its
practical utilisation for special purposes, it has been deemed expedient
to continue to give in this work an account of the principles underlying
the production and application of carburetted acetylene.

It has already been explained that acetylene is comparatively a less
efficient heating agent than it is an illuminating material, because, per
unit of volume, its calorific power is not so much greater than that of
coal-gas as is its illuminating capacity. It has also been shown that the
high upper explosive limit of mixtures of acetylene and air--a limit so
much higher than the corresponding figure with coal-gas and other gaseous
fuels--renders its employment in atmospheric burners (either for lighting
or for heating) somewhat troublesome, or dependent upon considerable
skill in the design of the apparatus. If, therefore, either the upper
explosive limit of acetylene could be reduced, or its calorific value
increased (or both), by mixing with it some other gas or vapour which
should not seriously affect its price and convenience as a self-luminous
illuminant, acetylene would compare more favourably with coal-gas in its
ready applicability to the most various purposes. Such a method has been
suggested by Heil, and has been found successful on the Continent. It
consists in adding to the acetylene a certain proportion of the vapour of
a volatile hydrocarbon, so as to prepare what is called "carburetted
acetylene." In all respects the method of making carburetted acetylene is
identical with that of making "air-gas," which was outlined in Chapter
I., viz., the acetylene coming from an ordinary generating plant is led
over or through a mass of petroleum spirit, or other similar product, in
a vessel which exposes the proper amount of superficial area to the
passing gas. In all respects save one the character of the product is
similar to that of air-gas, _i.e._, it is a mixture of a permanent
gas with a vapour; the vapour may possibly condense in part within the
mains if they are exposed to a falling temperature, and if the product is
to be led any considerable distance, deposition of liquid may occur
(conceivably followed by blockage of the mains) unless the proportion of
vapour added to the gas is kept below a point governed by local climatic
and similar conditions. But in one most important respect carburetted
acetylene is totally different from air-gas: partial precipitation of
spirit from air-gas removes more or less of the solitary useful
constituent of the material, reducing its practical value, and causing
the residue to approach or overpass its lower explosive limit (_cf._
Chapter I.); partial removal of spirit from carburetted acetylene only
means a partial reconversion of the material into ordinary acetylene,
increasing its natural illuminating power, lowering its calorific
intensity somewhat, and causing the residue to have almost its primary
high upper explosive limit, but essentially leaving its lower explosive
limit unchanged. Thus while air-gas may conceivably become inefficient
for every purpose if supplied from any distance in very cold weather, and
may even pass into a dangerous explosive within the mains; carburetted
acetylene can never become explosive, can only lose part of its special
heating value, and will actually increase in illuminating power.

It is manifest that, like air-gas, carburetted acetylene is of somewhat
indefinite composition, for the proportion of vapour, and the chemical
nature of that vapour, may vary. 100 litres of acetylene will take up 40
grammes of petroleum spirit to yield 110 litres of carburetted acetylene
evidently containing 9 per cent. of vapour, or 100 litres of acetylene
may be made to absorb as much as 250 grammes of spirit yielding 200
litres of carburetted acetylene containing 50 per cent. of vapour; while
the petroleum spirit may be replaced, if prices are suitable, by benzol
or denatured alcohol.

The illuminating power of acetylene carburetted with petroleum spirit has
been examined by Caro, whose average figures, worked out in British
units, are:


_Self-luminous._ | _Incandescent_
1 litre = 1.00 candle. | 1 litre = 3.04 candles.
1 cubic foot = 28.4 candles. | 1 cubic foot = 86.2 candles.
1 candle = 1.00 litre. | 1 candle = 0.33 litre.
1 candle = 0.035 cubic foot. | 1 candle = 0.012 cubic foot.

Those results may be compared with those referring to air-gas, which
emits in incandescent burners from 3.0 to 12.4 candles per cubic foot
according to the amount of spirit added to the air and the temperature to
which the gas is exposed.

The calorific values of carburetted acetylene (Caro), and those of other
gaseous fuels are:

Large Calories per
_ Cubic Foot.
| (Lewes) . 320
| (Gand) . 403
Ordinary acetylene . . | (Heil) . 365
| ___
|_Mean . . 363

| Maximum . 680
Carburetted acetylene . . | Minimum . 467
(petroleum spirit) | ___
|_Mean . . 573

Carburetted acetylene (50 per cent. benzol by volume) 685
Carburetted acetylene (50 per cent. alcohol by volume) 364
Coal-gas (common, unenriched) . . . . . 150
| Maximum . 178
Air-gas, self-luminous flame | Minimum . 57
| ___
|_Mean . . . 114
| Maximum . 26
Air-gas, non-luminous flame | Minimum . 18
| ___
|_Mean . . . 22

Water-gas (Strache) from coke . . . . . 71
Mond gas (from bituminous coal) . . . . . 38
Semi-water-gas from coke or anthracite . . . 36
Generator (producer) gas . . . . . . 29

Besides its relatively low upper explosive limit, carburetted acetylene
exhibits a higher temperature of ignition than ordinary acetylene, which
makes it appreciably safer in presence of a naked light. It also
possesses a somewhat lower flame temperature and a slower speed of
propagation of the explosive wave when mixed with air. These data are:

| | | | |
| | Explosive | Temperature. | |
| | Limits. | Degrees C. | Explosive |
| |19 mm. Tube. | | Explosive |
| |_____________|__________________| Wave. |
| | | | | | Metres per |
| | | |Of Igni-| | Second. |
| |Lower.|Upper.| tion. |Of Flame.| |
| | | | | | |
| Acetylene (theoretical)| --- | --- | --- |1850-2420| --- |
| " (observed) | 3.35 | 52.3 | 480 |1630-2020| 0.18-100 |
| Carburetted \ from | 2.5 | 10.2 | 582 | 1620 | 3.2 |
| acetylene / . . to | 5.4 | 30.0 | 720 | 1730 | 5.3 |
| Carburetted acetylene\ | 3.4 | 22.0 | --- | 1820 | 1.3 |
| (benzol) . . . / | | | | | |
| Carburetted acetylene\ | 3.1 | 12.0 | --- | 1610 | 1.1 |
| (alcohol) . . . / | | | | | |
| Air-gas, self-luminous\|15.0 | 50.0 | --- |1510-1520| --- |
| flame . . . . /| | | | | |
| Coal-gas . . . | 7.9 | 19.1 | 600 | --- | --- |

In making carburetted acetylene, the pressure given by the ordinary
acetylene generator will be sufficient to drive the gas through the
carburettor, and therefore there will be no expense involved beyond the
cost of the spirit vaporised. Thus comparisons may fairly be made between
ordinary and carburetted acetylene on the basis of material only, the
expense of generating the original acetylene being also ignored. In Great
Britain the prices of calcium carbide, petroleum spirit, and 90s benzol
delivered in bulk in country places may be taken at 15L per ton, and
1s. per gallon respectively, petroleum spirit having a specific
gravity of 0.700 and benzol of 0.88. On this basis, a unit volume (100
cubic metres) of plain acetylene costs 1135d., of "petrolised"
acetylene containing 66 per cent. of acetylene costs 1277d., and
of "benzolised" acetylene costs 1180d. In other words, 100 volumes
of plain acetylene, 90 volumes of petrolised acetylene, and 96 volumes of
benzolised acetylene are of equal pecuniary value. Employing the data
given in previous tables, it appears that 38.5 candles can be won from
plain acetylene in a self-luminous burner, and 103 candles therefrom in
an incandescent burner at the same price as 25.5-29.1 and 78-87 candles
can be obtained from carburetted acetylene; whence it follows that at
English prices petrolised acetylene is more expensive as an illuminant in
either system of combustion than the simple gas, while benzolised
acetylene, burnt under the mantle only, is more nearly equal to the
simple gas from a pecuniary aspect. But considering the calorific value,
it appears that for a given sum of money only 363 calories can be
obtained from plain acetylene, while petrolised acetylene yields 516, and
benzolised acetylene 658; so that for all heating or cooking purposes
(and also for driving small motors) carburetted acetylene exhibits a
notable economy. Inasmuch as the partial saturation of acetylene with any
combustible vapour is an operation of extreme simplicity, requiring no
power or supervision beyond the occasional recharging of the carburettor,
it is manifest that the original main coming from the generator supplying
any large establishment where much warming, cooking (or motor driving)
might conveniently be done with the gas could be divided within the
plant-house, one branch supplying all, or nearly all, the lighting
burners with plain acetylene, and the other branch communicating with a
carburettor, so that all, or nearly all, the warming and cooking stoves
(and the motor) should be supplied with the more economical carburetted
acetylene. Since any water pump or similar apparatus would be in an
outhouse or basement, and the most important heating stove (the cooker)
be in the kitchen, such an arrangement would be neither complicated nor
involve a costly duplication of pipes.

It follows from the fact that even a trifling proportion of vapour
reduces the upper limit of explosibility of mixtures of acetylene with
air, that the gas may be so lightly carburetted as not appreciably to
suffer in illuminating power when consumed in self-luminous jets, and yet
to burn satisfactorily in incandescent burners, even if it has been
generated in an apparatus which introduces some air every time the
operation of recharging is performed. To carry out this idea, Caro has
suggested that 5 kilos. of petroleum spirit should be added to the
generator water for every 50 cubic metres of gas evolved, _i.e._, 1
lb. per 160 cubic feet, or, say, 1 gallon per 1000 cubic feet, or per 200
lb. of carbide decomposed. Caro proposed this addition in the case of
central installations supplying a district where the majority of the
consumers burnt the gas in self-luminous jets, but where a few preferred
the incandescent system; but it is clearly equally suitable for
employment in all private plants of sufficient magnitude.

A lowering of the upper limit of explosibility is also produced by the
presence of the acetone which remains in acetylene when obtained from a
cylinder holding the compressed gas (_cf._ Chapter XI.). According
to Wolff and Caro such gas usually carries with it from 30 to 60 grammes
of acetone vapour per cubic metre, _i.e._, 1.27 grammes per cubic
foot on an average; and this amount reduces the upper limit of
explosibility by about 16 per cent., so that to this extent the gas
behaves more smoothly in an incandescent burner of imperfect design.

Lepinay has described some experiments on the comparative technical value
of ordinary acetylene, carburetted acetylene, denatured alcohol and
petroleum spirit as fuels for small explosion engines. One particular
motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per
hour at full load; but when it was supplied with carburetted acetylene
its consumption fell to 150 litres of acetylene and 700 grammes of spirit
(specific gravity 0.680). A 1-1/4 h.p. engine running light required 48
grammes of 90 per cent. alcohol per horse-power-hour and 66 litres of
acetylene; at full load it took 220 grammes of alcohol and 110 litres of
acetylene. A 6 h.p. engine at full load required 62 litres of acetylene
carburetted with 197 grammes of petroleum spirit per horse-power-hour
(uncorrected); while a similar motor fed with low-grade Taylor fuel-gas
took 1260 litres per horse-power-hour, but on an average developed the
same amount of power from 73 litres when 10 per cent. of acetylene was
added to the gas. Lepinay found that with pure acetylene ignition of the
charge was apt to be premature; and that while the consumption of
carburetted acetylene in small motors still materially exceeded the
theoretical, further economics could be attained, which, coupled with the
smooth and regular running of an engine fed with the carburetted gas,
made carburetted acetylene distinctly the better power-gas of the two.



In all that was said in Chapters II., III., IV., and V. respecting the
generation and employment of acetylene, it was assumed that the gas would
be produced by the interaction of calcium carbide and water, either by
the consumer himself, or in some central station delivering the acetylene
throughout a neighbourhood in mains. But there are other methods of using
the gas, which have now to be considered.

COMPRESSED ACETYLENE.--In the first place, like all other gases,
acetylene is capable of compression, or even of conversion into the
liquid state; for as a gas, the volume occupied by any given weight of it
is not fixed, but varies inversely with the pressure under which it is
stored. A steel cylinder, for instance, which is of such size as to hold
a cubic foot of water, also holds a cubic foot of acetylene at
atmospheric pressure, but holds 2 cubic feet if the gas is pumped into it
to a pressure of 2 atmospheres, or 30 lb. per square inch; while by
increasing the pressure to 21.53 atmospheres at 0 deg. C. (Ansdell, Willson
and Suckert) the gas is liquefied, and the vessel may then contain 1
cubic foot of liquid acetylene, which is equal to some 400 cubic feet of
gaseous acetylene at normal pressure. It is clear that for many purposes
acetylene so compressed or liquefied would be convenient, for if the
cylinders could be procured ready charged, all troubles incidental to
generation would be avoided. The method, however, is not practically
permissible; because, as pointed out in Chapters II. and VI., acetylene
does not safely bear compression to a point exceeding 2 atmospheres; and
the liability to spontaneous dissociation or explosion in presence of
spark or severe blow, which is characteristic of compressed gaseous
acetylene, is greatly enhanced if compression has been pushed to the
point of liquefaction.

However, two methods of retaining the portability and convenience of
compressed acetylene with complete safety have been discovered. In one,
due to the researches of Claude and Hess, the gas is pumped under
pressure into acetone, a combustible organic liquid of high solvent power,
which boils at 56 deg. C. As the solvent capacity of most liquids for
most gases rises with the pressure, a bottle partly filled with acetone
may be charged with acetylene at considerable effective pressure until
the vessel contains much more than its normal quantity of gas; and when
the valve is opened the surplus escapes, ready for employment, leaving
the acetone practically unaltered in composition or quantity, and fit to
receive a fresh charge of gas. In comparison with liquefied acetylene,
its solution in acetone under pressure is much safer; but since the
acetone expands during absorption of gas, the bottle cannot be entirely
filled with liquid, and therefore either at first, or during consumption
(or both), above the level of the relatively safe solution, the cylinder
contains a certain quantity of gaseous acetylene, which is compressed
above its limit of safety. The other method consists in pumping acetylene
under pressure into a cylinder apparently quite full of some highly
porous solid matter, like charcoal, kieselguhr, unglazed brick, &c. This
has the practical result that the gas is held under a high state of
compression, or possibly as a liquid, in the minute crevices of the
material, which are almost of insensible magnitude; or it may be regarded
as stored in vessels whose diameter is less than that in which an
explosive wave can be propagated (_cf._ Chapter VI.).

DISSOLVED ACETYLENE.--According to Fouche, the simple solution of
acetylene in acetone has the same coefficient of expansion by heat as
that of pure acetone, viz., 0.0015; the corresponding coefficient of
liquefied acetylene is 0.007 (Fouche), or 0.00489 (Ansdell) _i.e._,
three or five times as much. The specific gravity of liquid acetylene is
0.420 at 16.4 deg. C. (Ansdell), or 0.528 at 20.6 deg. C. (Willson and
Suckert); while the density of acetylene dissolved in acetone is 0.71 at 15
deg. C. (Claude). The tension of liquefied acetylene is 21.53 atmospheres at
0 deg. C., and 39.76 atmospheres at 20.15 deg. C. (Ansdell); 21.53 at 0 deg.
C., and 39.76 at 19.5 deg. C. (Willson and Suckert); or 26.5 at 0 deg. C.,
and 42.8 at 20.0 deg. C. (Villard). Averaging those results, it may be said
that the tension rises from 23.2 atmospheres at 0 deg. C. to 40.77 at 20 deg.
C., which is an increment of 1/26 or 0.88 atmosphere, per 1 deg. Centigrade;
while, of course, liquefied acetylene cannot be kept at all at a temperature
of 0 deg. unless the pressure is 21 atmospheres or upwards. The solution of
acetylene in acetone can be stored at any pressure above or below that of
the atmosphere, and the extent to which the pressure will rise as the
temperature increases depends on the original pressure. Berthelot and
Vieille have shown that when (_a_) 301 grammes of acetone are
charged with 69 grammes of acetylene, a pressure of 6.74 atmospheres at
14.0 deg. C. rises to 10.55 atmospheres at 35.7 deg. C.; (_b_) 315 grammes
of acetone are charged with 118 grammes of acetylene, a pressure of 12.25
atmospheres at 14.0 deg. C. rises to 19.46 at 36.0 deg. C.; (_c_) 315
grammes of acetone are charged with 203 grammes of acetylene, a pressure
of 19.98 atmospheres at 13.0 deg. C. rises to 30.49 at 36.0 deg. C.
Therefore in (_a_) the increase in pressure is 0.18 atmosphere, in (_b_)
O.33 atmosphere, and in (_c_) 0.46 atmosphere per 1 deg. Centigrade
within the temperature limits quoted. Taking case (_b_) as the
normal, it follows that the increment in pressure per 1 deg. C. is 1/37
(usually quoted as 1/30); so that, measured as a proportion of the
existing pressure, the pressure in a closed vessel containing a solution
of acetylene in acetone increases nearly as much (though distinctly less)
for a given rise in temperature as does the pressure in a similar vessel
filled with liquefied acetylene, but the absolute increase is roughly
only one-third with the solution as with the liquid, because the initial
pressure under which the solution is stored is only one-half, or less,
that at which the liquefied gas must exist.

Supposing, now, that acetylene contained in a closed vessel, either as
compressed gas, as a solution in acetone, or as a liquid, were brought to
explosion by spark or shock, the effects capable of production have to be
considered. Berthelot and Vieille have shown that if gaseous acetylene is
stored at a pressure of 11.23 kilogrammes per square centimetre,
[Footnote: 1 kilo. per sq. cm. is almost identical with 1 atmosphere, or
15 lb. per sq. inch.] the pressure after explosion reaches 92.33
atmospheres on an average, which is an increase of 8.37 times the
original figure; if the gas is stored at 21.13 atmospheres, the mean
pressure after explosion is 213.15 atmospheres, or 10.13 times the
original amount. If liquid acetylene is tested similarly, the original
pressure, which must clearly be more than 21.53 atmospheres (Ansdell) at
0 deg. C., may rise to 5564 kilos, per square centimetre, as Berthelot and
Vieille observed when a steel bomb having a capacity of 49 c.c. was
charged with 18 grammes of liquefied acetylene. In the case of the
solution in acetone, the magnitudes of the pressures set up are of two
entirely different orders according as the original pressure 20
atmospheres or somewhat less; but apart from this, they vary considerably
with the extent to which the vessel is filled with the liquid, and they
also depend on whether the explosion is produced in the solution or in
the gas space above. Taking the lower original pressure first, viz., 10
atmospheres, when a vessel was filled with solution to 33 per cent. of
its capacity, the pressure after explosion reached about 95 atmospheres
if the spark was applied to the gas space; but attained 117.4 atmospheres
when the spark was applied to the acetone. When the vessel was filled 56
per cent. full, the pressures after explosion reached about 89, or 155
atmospheres, according as the gas or the liquid was treated with the
spark. But when the original pressure was 20 atmospheres, and the vessel
was filled to 35 per cent. of its actual capacity with solution, the
final pressures ranged from 303 to 568 atmospheres when the gas was
fired, and from 2000 to 5100 when the spark was applied to the acetone.
Examining these figures carefully, it will be seen that the phenomena
accompanying the explosion of a solution of acetylene in acetone resemble
those of the explosion of compressed gaseous acetylene when the original
pressure under which the solution is stored is about 10 atmospheres; but
resemble those of the explosion of liquefied acetylene when the original
pressure of the solution reaches 20 atmospheres, this being due to the
fact that at an original pressure of 10 atmospheres the acetone itself
does not explode, but, being exothermic, rather tends to decrease the
severity of the explosion; whereas at an original pressure of 20
atmospheres the acetone does explode (or burn), and adds its heat of
combustion to the heat evolved by the acetylene. Thus at 10 atmospheres
the presence of the acetone is a source of safety; but at 20 atmospheres
it becomes an extra danger.

Since sound steel cylinders may easily be constructed to boar a pressure
of 250 atmospheres, but would be burst by a pressure considerably less
than 5000 atmospheres, it appears that liquefied acetylene and its
solution in acetone at a pressure of 20 atmospheres are quite unsafe; and
it might also seem that both the solution at a pressure of 10 atmospheres
and the simple gas compressed to the same limit should be safe. But there
is an important difference here, in degree if not in kind, because, given
a cylinder of known capacity containing (1) gaseous acetylene compressed
to 10 atmospheres, or (2) containing the solution at the same pressure,
if an explosion were to occur, in case (1) the whole contents would
participate in the decomposition, whereas in case (2), as mentioned
already, only the small quantity of gaseous acetylene above the solution
would be dissociated.

It is manifest that of the three varieties of compressed acetylene now
under consideration, the solution in acetone is the only one fit for
general employment; but it exhibits the grave defects (_a_) that the
pressure under which it is prepared must be so small that the pressure in
the cylinders can never approach 20 atmospheres in the hottest weather or
in the hottest situation to which they may be exposed, (_b_) that
the gas does not escape smoothly enough to be convenient from large
vessels unless those vessels are agitated, and (_c_) that the
cylinders must always be used in a certain position with the valve at the
top, lest part of the liquid should run out into the pipes. For these
reasons the simple solution of acetylene in acetone has not become of
industrial importance; but the processes of absorbing either the gas, or
better still its solution in acetone, in porous matter have already
achieved considerable success. Both methods have proved perfectly safe
and trustworthy; but the combination of the acetone process with the
porous matter makes the cylinders smaller per unit volume of acetylene
they contain. Several varieties of solid matter appear to work
satisfactorily, the only essential feature in their composition being
that they shall possess a proper amount of porosity and be perfectly free
from action upon the acetylene or the acetone (if present). Lime does
attack acetone in time, and therefore it is not a suitable ingredient of
the solid substance whenever acetylene is to be compressed in conjunction
with the solvent; so that at present either a light brick earth which has
a specific gravity of 0.5 is employed, or a mixture of charcoal with
certain inorganic salts which has a density of 0.3, and can be introduced
through a small aperture into the cylinder in a semi-fluid condition.
Both materials possess a porosity of 80 per cent., that is to say, when a
cylinder is apparently filled quite full, only 20 per cent, of the space
is really occupied by the solid body, the remaining 80 per cent, being
available for holding the liquid or the compressed gas. If all
comparisons as to degree of explosibility and effects of explosion are
omitted, an analogy may be drawn between liquefied acetylene or its
compressed solution in acetone and nitroglycerin, while the gas or
solution of the gas absorbed in porous matter resembles dynamite.
Nitroglycerin is almost too treacherous a material to handle, but as an
explosive (which in reason absorbed or dissolved acetylene is not)
dynamite is safe, and even requires special arrangements to explode it.

In Paris, where the acetone process first found employment on a large
scale, the company supplying portable cylinders to consumers uses large
storage vessels filled, as above mentioned, apparently full of porous
solid matter, and also charged to about 43 per cent, of their capacity
with acetone, thus leaving about 37 per cent. of the apace for the
expansion which occurs as the liquid takes up the gas. Acetylene is
generated, purified, and thoroughly dried according to the usual methods;
and it is then run through a double-action pump which compresses it first
to a pressure of 3.5 kilos., next to a pressure of 3.5 x 3.5 = 12 kilos,
per square centimetre, and finally drives it into the storage vessels.
Compression is effected in two stages, because the process is accompanied
by an evolution of much heat, which might cause the gas to explode during
the operation; but since the pump is fitted with two cylinders, the
acetylene can be cooled after the first compression. The storage vessels
then contain 100 times their apparent volume of acetylene; for as the
solubility of acetylene in acetone at ordinary temperature and pressure
is about 25 volumes of gas in 1 of liquid, a vessel holding 100 volumes
when empty takes up 25 x 43 = 1000 volumes of acetylene roughly at
atmospheric pressure; which, as the pressure is approximately 10
atmospheres, becomes 1000 x 10 = 10,000 volumes per 100 normal capacity,
or 100 times the capacity of the vessel in terms of water. From these
large vessels, portable cylinders of various useful dimensions, similarly
loaded with porous matter and acetone, are charged simply by placing them
in mutual contact, thus allowing the pressure and the surplus gas to
enter the small one; a process which has the advantage of renewing the
small quantity of acetone vaporised from the consumers' cylinders as the
acetylene is burnt (for acetone is somewhat volatile, cf. Chapter X.), so
that only the storage vessels ever need to have fresh solvent introduced.

Where it is procurable, the use of acetylene compressed in this fashion
is simplicity itself; for the cylinders have only to be connected with
the house service-pipes through a reducing valve of ordinary
construction, set to give the pressure which the burners require. When
exhausted, the bottle is simply replaced by another. Manifestly, however,
the cost of compression, the interest on the value of the cylinders, and
the carriage, &c., make the compressed gas more expensive per unit of
volume (or light) than acetylene locally generated from carbide and
water; and indeed the value of the process does not lie so much in the
direction of domestic illumination as in that of the lighting, and
possibly driving, of vehicles and motor-cars--more especially in the
illumination of such vehicles as travel constantly, or for business
purposes, over rough road surfaces and perform mostly out-and-home
journeys. Nevertheless, absorbed acetylene may claim close attention for
one department of household illumination, viz., the portable table-lamp;
for the base of such an apparatus might easily be constructed to imitate
the acetone cylinder, and it could be charged by simple connexion with a
larger one at intervals. In this way the size of the lamp for a given
number of candle-hours would be reduced below that of any type of actual
generator, and the troubles of after-generation, always more or less
experienced in holderless generators, would be entirely done away with.
Dissolved acetylene is also very useful for acetylene welding or
autogenous soldering.

The advantages of compressed and absorbed acetylene depend on the small
bulk and weight of the apparatus per unit of light, on the fact that no
amount of agitation can affect the evolution of gas (as may happen with
an ordinary acetylene generator), on the absence of any liquid which may
freeze in winter, and on there being no need for skilled attention except
when the cylinders are being changed. These vessels weigh between 2.5 and
3 kilos, per 1 litre capacity (normal) and since they are charged with
100 times their apparent volume of acetylene, they may be said to weigh 1
kilo, per 33 litres of available acetylene, or roughly 2 lb. per cubic
foot, or, again, if half-foot burners are used, 2 lb. per 36 candle-
hours. According to Fouche, if electricity obtained from lead
accumulators is compared with acetylene on the basis of the weight of
apparatus needed to evolve a certain quantify of light, 1 kilo, of
acetylene cylinder is equal to 1.33 kilos, of lead accumulator with arc
lamps, or to 4 kilos. of accumulator with glow lamps; and moreover the
acetylene cylinder can be charged and discharged, broadly speaking, as
quickly or as slowly as may be desired; while, it may be added, the same
cylinder will serve one or more self-luminous jets, one or more
incandescent burners, any number and variety of heating apparatus,
simultaneously or consecutively, at any pressure which may be required.
From the aspect of space occupied, dissolved acetylene is not so
concentrated a source of artificial light as calcium carbide; for 1
volume of granulated carbide is capable of omitting as much light as 4
volumes of compressed gas; although, in practice, to the 1 volume of
carbide must be added that of the apparatus in which it is decomposed.

LIQUEFIED ACETYLENE.--In most civilised countries the importation,
manufacture, storage, and use of liquefied acetylene, or of the gas
compressed to more than a fraction of one effective atmosphere, is quite
properly prohibited by law. In Great Britain this has been done by an
Order in Council dated November 26, 1897, which specifies 100 inches of
water column as the maximum to which compression may be pushed. Power
being retained, however, to exempt from the order any method of
compressing acetylene that might be proved safe, the Home Secretary
issued a subsequent Order on March 28, 1898, permitting oil-gas
containing not more than 20 per cent, by volume of acetylene (see below)
to be compressed to a degree not exceeding 150 lb. per square inch,
_i.e._, to about 10 atmospheres, provided the gases are mixed
together before compression; while a third Order, dated April 10, 1901,
allows the compression of acetylene into cylinders filled as completely
as possible with porous matter, with or without the presence of acetone,
to a pressure not exceeding 150 lb. per square inch provided the
cylinders themselves have been tested by hydraulic pressure for at least
ten minutes to a pressure not less than double [Footnote: In France the
cylinders are tested to six times and in Russia to five times their
working pressure.] that which it is intended to use, provided the solid
substance is similar in every respect to the samples deposited at the
Home Office, provided its porosity does not exceed 80 per cent., provided
air is excluded from every part of the apparatus before the gas is
compressed, provided the quantity of acetone used (if used at all) is not
sufficient to fill the porosity of the solid, provided the temperature is
not permitted to rise during compression, and provided compression only
takes place in premises approved by H.M.'s Inspectors of Explosives.

DILUTED ACETYLENE.--Acetylene is naturally capable of admixture or
dilution with any other gas or vapour; and the operation may be regarded
in either of two ways; (1) as a, means of improving the burning qualities
of the acetylene itself, or (2) as a means of conferring upon some other
gas increased luminosity. In the early days of the acetylene industry,
generation was performed in so haphazard a fashion, purification so
generally omitted, and the burners were so inefficient, that it was
proposed to add to the gas a comparatively small proportion of some other
gaseous fluid which should be capable of making it burn without
deposition of carbon while not seriously impairing its latent
illuminating power. One of the first diluents suggested was carbon
dioxide (carbonic acid gas), because this gas is very easy and cheap to
prepare; and because it was stated that acetylene would bear an addition
of 5 or even 8 per cent, of carbon dioxide and yet develop its full
degree of luminosity. This last assertion requires substantiation; for it
is at least a grave theoretical error to add a non-inflammable gas to a
combustible one, as is seen in the lower efficiency of all flames when
burning in common air in comparison with that which they exhibit in
oxygen; while from the practical aspect, so harmful is carbon dioxide in
an illuminating gas, that coal-gas and carburetted water-gas are
frequently most rigorously freed from it, because a certain gain in
illuminating power may often thus be achieved more cheaply than by direct
enrichment of the gas by addition of hydrocarbons. Being prepared from
chalk and any cheap mineral acid, hydrochloric by preference, in the
cold, carbon dioxide is so cheap that its price in comparison with that
of acetylene is almost _nil_; and therefore, on the above
assumption, 105 volumes of diluted acetylene might be made essentially
for the same price as 100 volumes of neat acetylene, and according to
supposition emit 5 per cent. more light per unit of volume.

It is reported that several railway trains in Austria are regularly
lighted with acetylene containing 0.4 to 1.0 per cent. of carbon dioxide
in order to prevent deposition of carbon at the burners. The gas is
prepared according to a patent process which consists in adding a certain
proportion of a "carbonate" to the generator water. In the United
Kingdom, also, there are several installations supplying an acetylene
diluted with carbon dioxide, the gas being produced by putting into that
portion of a water-to-carbide generator which lies nearest to the water-
supply some solid carbonate like chalk, and using a dilute acid to attack
the material. Other inventors have proposed placing a solid acid, like
oxalic, in the former part of a generator and decomposing it with a
carbonate solution; or they have suggested putting into the generator a
mixture of a solid acid and a solid soluble carbonate, and decomposing it
with plain water.

Clearly, unless the apparatus in which such mixtures as these are
intended to be prepared is designed with considerable care, the amount of
carbon dioxide in the gas will be liable to vary, and may fall to zero.
If any quantity of carbide present has been decomposed in the ordinary
way, there will be free calcium hydroxide in the generator; and if the
carbon dioxide comes into contact with this, it will be absorbed, unless
sufficient acid is employed to convert the calcium carbonate (or
hydroxide) into the corresponding normal salt of calcium. Similarly,
during purification, a material containing any free lime would tend to
remove the carbon dioxide, as would any substance which became alkaline
by retaining the ammonia of the crude gas.

It cannot altogether be granted that the value of a process for diluting
acetylene with carbon dioxide has been established, except in so far as
the mere presence of the diluent may somewhat diminish the tendency of
the acetylene to polymerise as it passes through a hot burner (_cf._
Chapter VIII.). Certainly as a fuel-gas the mixture would be less
efficient, and the extra amount of carbon dioxide produced by each flame
is not wholly to be ignored. Moreover, since properly generated and
purified acetylene can be consumed in proper burners without trouble, all
reason for introducing carbon dioxide has disappeared.

MIXTURES OF ACETYLENE AND AIR.--A further proposal for diluting acetylene
was the addition to it of air. Apart from questions of explosibility,
this method has the advantage over that of adding carbon dioxide that the
air, though not inflammable, is, in virtue of its contained oxygen, a
supporter of combustion, and is required in a flame; whereas carbon
dioxide is not only not a supporter of combustion, but is actually a
product thereof, and correspondingly more objectionable. According to
some experiments carried out by Dufour, neat acetylene burnt under
certain conditions evolved between 1.0 and 1.8 candle-power per litre-
hour; a mixture of 1 volume of acetylene with 1 volume of air evolved 1.4
candle-power; a mixture of 1 volume of acetylene with 1.2 volumes of air,
2.25 candle-power; and a mixture of 1 volume of acetylene with 1.3
volumes of air, 2.70 candle-power per litre-hour of acetylene in the
several mixtures. Averaging the figures, and calculating into terms of
acetylene (only) burnt, Dufour found neat acetylene to develop 1.29
candle-power per litre-hour, and acetylene diluted with air to develop
1.51 candle-power. When, however, allowance is made for the cost and
trouble of preparing such mixtures the advantage of the process
disappears; and moreover it is accompanied by too grave risks, unless
conducted on a largo scale and under most highly skilled supervision, to
be fit for general employment.

Fouche, however, has since found the duty, per cubic foot of neat
acetylene consumed in a twin injector burner at the most advantageous
rate of 3.2 inches, to be as follows for mixtures with air in the
proportions stated:

Percentage of air 0 17 27 33.5
Candles per cubic feet 38.4 36.0 32.8 26.0

At lower pressures, the duty of the acetylene when diluted appears to be
relatively somewhat higher. Figures which have been published in regard
to a mixture of 30 volumes of air and 70 volumes of acetylene obtained by
a particular system of producing such a mixture, known as the "Molet-
Boistelle," indicate that the admixture of air causes a slight increase
in the illuminating duty obtained from the acetylene in burners of
various sizes. The type of burner and the pressure employed in these
experiments were not, however, stated. This system has been used at
certain stations on the "Midi" railway in France. Nevertheless even where
the admixture of air to acetylene is legally permissible, the risk of
obtaining a really dangerous product and the nebulous character of the
advantages attainable should preclude its adoption.

In Great Britain the manufacture, importation, storage, and use of
acetylene mixed with air or oxygen, in all proportions and at all
pressures, with or without the presence of other substances, is
prohibited by an Order in Council dated July 1900; to which prohibition
the mixture of acetylene and air that takes place in a burner or
contrivance in which the mixture is intended to be burnt, and the
admixture of air with acetylene that may unavoidably occur in the first
use or recharging of an apparatus (usually a water-to-carbide generator),
properly designed and constructed with a view to the production of pure
acetylene, are the solitary exceptions.

MIXED CARBIDES.--In fact the only processes for diluting acetylene which
possess real utility are that of adding vaporised petroleum spirit or
benzene to the gas, as was described in Chapter X. under the name of
carburetted acetylene, and one other possible method of obtaining a
diluted acetylene directly from the gas-generator, to which a few words
will now be devoted. [Footnote: Mixtures of acetylene with relatively
large proportions of other illuminating gases, such as are referred to on
subsequent pages, are also, from one aspect, forms of diluted acetylene.]
Calcium carbide is only one particular specimen of a large number of
similar metallic compounds, which can be prepared in the electric
furnace, or otherwise. Some of those carbides yield acetylene when
treated with water, some are not attacked, some give liquid products, and
some yield methane, or mixtures of methane and hydrogen. Among the latter
is manganese carbide. If, then, a mixture of manganese carbide and
calcium carbide is put into an ordinary acetylene generator, the gas
evolved will be a mixture of acetylene with methane and hydrogen in
proportions depending upon the composition of the carbide mixture. It is
clear that a suitable mixture of the carbides might be made by preparing
them separately and bulking the whole in the desired proportions; while
since manganese carbide can be won in the electric furnace, it might be
feasible to charge into such a furnace a mixture of lime, coke, and
manganese oxide calculated to yield a simple mixture of the carbides or a
kind of double carbide. Following the lines which have been adopted in
writing the present book, it is not proposed to discuss the possibility
of making mixed carbides; but it may be said in brief that Brame and
Lewes have carried out several experiments in this direction, using
charges of lime and coke containing (_a_) up to 20 per cent. of
manganese oxide, and (_b_) more than 60 per cent. of manganese
oxide. In neither case did they succeed in obtaining a material which
gave a mixture of acetylene and methane when treated with water; in case
(_a_) they found the gas to be practically pure acetylene, so that
the carbide must have been calcium carbide only; in case (_b_) the
gas was mainly methane and hydrogen, so that the carbide must have been
essentially that of manganese alone. Mixed charges containing between 20
and 60 per cent. of manganese oxide remain to be studied; but whether
they would give mixed carbides or no, it would be perfectly simple to mix
ready-made carbides of calcium and manganese together, if any demand for
a diluted acetylene should arise on a sufficiently large scale. It is,
however, somewhat difficult to appreciate the benefits to be obtained
from forms of diluted acetylene other than those to which reference is
made later in this chapter.

There is, nevertheless, one modification of calcium carbide which, in a
small but important sphere, finds a useful _role_. It has been
pointed out that a carbide containing much calcium phosphide is usually
objectionable, because the gas evolved from it requires extra
purification, and because there is the (somewhat unlikely) possibility
that the acetylene obtained from such material before purification may be
spontaneously inflammable. If, now, to the usual furnace charge of lime
and coke a sufficient quantity of calcium phosphate is purposely added,
it is possible to win a mixture of calcium phosphide and carbide, or, as
Bradley, Read, and Jacobs call it, a "carbophosphide of calcium," having
the formula Ca_5C_6P_2, which yields a spontaneously inflammable mixture
of acetylene, gaseous phosphine, and liquid phosphine when treated with
water, and which, therefore, automatically gives a flame when brought
into contact with the liquid. The value of this material will be
described in Chapter XIII.

GAS-ENRICHING.--Other methods of diluting acetylene consist in adding a
comparatively small proportion of it to some other gas, and may be
considered rather as processes for enriching that other gas with
acetylene. Provided the second gas is well chosen, such mixtures exhibit
properties which render them peculiarly valuable for special purposes.
They have, usually, a far lower upper limit of explosibility than that of
neat acetylene, and they admit of safe compression to an extent greatly
exceeding that of acetylene itself, while they do not lose illuminating
power on compression. The second characteristic is most important, and
depends on the phenomena of "partial pressure," which have been referred
to in Chapter VI. When a single gas is stored at atmospheric pressure, it
is insensibly withstanding on all sides and in all directions a pressure
of roughly 15 lb. per square inch, which is the weight of the atmosphere
at sea-level; and when a mixture of two gases, X and Y, in equal volumes
is similarly stored it, regarded as an entity, is also supporting a
pressure of 15 lb. per square inch. But in every 1 volume of that mixture
there is only half a volume of X and Y each; and, ignoring the presence
of its partner, each half-volume is evenly distributed throughout a space
of 1 volume. But since the volume of a gas stands in inverse ratio to the
pressure under which it is stored, the half-volume of X in the 1 volume
of X + Y apparently stands at a pressure of half an atmosphere, for it
has expanded till it fills, from a chemical and physical aspect, the
space of 1 volume: suitable tests proving that it exhibits the properties
which a gas stored at a pressure of half an atmosphere should do.
Therefore, in the mixture under consideration, X and Y are both said to
be at a "partial pressure" of half an atmosphere, which is manifestly 7.5
lb. per square inch. Clearly, when a gas is an entity (either an element
or one single chemical compound) partial and total pressure are
identical. Now, it has been shown that acetylene ceases to be a safe gas
to handle when it is stored at a pressure of 2 atmospheres; but the limit
of safety really occurs when the gas is stored at a _partial_
pressure of 2 atmospheres. Neat acetylene, accordingly, cannot be
compressed above the mark 30 lb. shown on a pressure gauge; but diluted
acetylene (if the diluent is suitable) may be compressed in safety till
the partial pressure of the acetylene itself reaches 2 atmospheres. For
instance, a mixture of equal volumes of X and Y (X being acetylene)
contains X at a partial pressure of half the total pressure, and may
therefore be compressed to (2 / 1/2 =) 4 atmospheres before X reaches the
partial pressure of 2 atmospheres; and therewith the mixture is brought
just to the limit of safety, any effect of Y one way or the other being
neglected. Similarly, a mixture of 1 volume of acetylene with 4 volumes
of Y may be safely compressed to a pressure of (2 / 1/5 =) 10
atmospheres, or, broadly, a mixture in which the percentage of acetylene
is _x_ may be safely compressed to a pressure not exceeding (2 /
_x_/100) atmospheres. This fact permits acetylene after proper
dilution to be compressed in the same fashion as is allowable in the case
of the dissolved and absorbed gas described above.

If the latent illuminating power of acetylene is not to be wasted, the
diluent must not be selected without thought. Acetylene burns with a very
hot flame, the luminosity of which is seriously decreased if the
temperature is lowered. As mentioned in Chapter VIII., this may be done
by allowing too much air to enter the flame; but it may also be effected
to a certain extent by mixing with the acetylene before combustion some
combustible gas or vapour which burns at a lower temperature than
acetylene itself. Manifestly, therefore, the ideal diluent for acetylene
is a substance which possesses as high a flame temperature as acetylene
and a certain degree of intrinsic illuminating power, while the lower the
flame temperature of the diluent and the less its intrinsic illuminating
power, the less efficiently will the acetylene act as an enriching
material. According to Love, Hempel, Wedding, and others, if acetylene is
mixed with coal-gas in amounts up to 8 per cent. or thereabouts, the
illuminating power of the mixture increases about 1 candle for every 1
per cent. of acetylene present: a fact which is usually expressed by
saying that with coal-gas the enrichment value of acetylene is 1 candle
per 1 per cent. Above 8 per cent., the enrichment value of acetylene
rises, Love having found an increase in illuminating power, for each 1
per cent. of acetylene in the mixture, of 1.42 candles with 11.28 per
cent. of acetylene; and of 1.54 candles with 17.62 per cent. of
acetylene. Theoretically, if the illuminating power of acetylene is taken
at 240 candles, its enrichment value should be (240 / 100 =) 2.4 candles
per 1 per cent.; and since, in the case of coal-gas, its actual
enrichment value falls seriously below this figure, it is clear that
coal-gas is not an economical diluent for it. Moreover, coal-gas can be
enriched by other methods much more cheaply than with acetylene. Simple
("blue") water-gas, according to Love, requires more than 10 per cent. of
acetylene to be added to it before a luminous flame is produced; while a
mixture of 20.3 per cent. of acetylene and 79.7 per cent. of water-gas
had an illuminating power of 15.47 candles. Every addition to the
proportion of acetylene when it amounted to 20 per cent. and upwards of
the mixture had a very appreciable effect on the illuminating power of
the latter. Thus with 27.84 per cent. of acetylene, the illuminating
power of the mixture was 40.87 candles; with 38.00 per cent. of acetylene
it was 73.96 candles. Acetylene would not be an economical agent to
employ in order to render water-gas an illuminating gas of about the
quality of coal-gas, but the economy of enrichment of water-gas by
acetylene increases rapidly with the degree of enrichment demanded of it.
Carburetted water-gas which, after compression under 16 atmospheres
pressure, had an illuminating power of about 17.5 candles, was enriched
by additions of acetylene. 4.5 per cent. of acetylene in the mixture gave
an illuminating power of 22.69 candles; 8.4 per cent., 29.54 candles;
11.21 per cent., 35.05 candles; 15.06 per cent., 42.19 candles; and 21.44
per cent., 52.61 candles. It is therefore evident that the effect of
additions of acetylene on the illuminating power of carburetted water-gas
is of the same order as its effect on coal-gas. The enrichment value of
the acetylene increases with its proportion in the mixture; but only when
the proportion becomes quite considerable, and, therefore, the gas of
high illuminating power, does enrichment by acetylene become economical.
Methane (marsh-gas), owing to its comparatively high flame temperature,
and to the fact that it has an intrinsic, if small, illuminating power,
is a better diluent of acetylene than carbon monoxide or hydrogen, in
that it preserves to a greater extent the illuminative value of the

Actually comparisons of the effect of additions of various proportions of
a richly illuminating gas, such as acetylene, on the illuminative value
of a gas which has little or no inherent illuminating power, are largely
vitiated by the want of any systematic method for arriving at the
representative illuminative value of any illuminating gas. A statement
that the illuminating power of a gas is _x_ candles is, strictly
speaking, incomplete, unless it is supplemented by the information that
the gas during testing was burnt (1) in a specified type of burner, and
(2) either at a specified fixed rate of consumption or so as to afford a
light of a certain specified intensity. There is no general agreement,
even in respect of the statutory testing of the illuminating power of
coal-gas supplies, as to the observance of uniform conditions of burning
of the gas under test, and in regard to more highly illuminating gases
there is even greater diversity of conditions. Hence figures such as
those quoted above for the enrichment value of acetylene inevitably show
a certain want of harmony which is in reality due to the imperfection or
incompleteness of the modes of testing employed. Relatively to another,
one gas appears advantageously merely in virtue of the conditions of
assessing illuminating power having been more favourable to it. Therefore
enrichment values, such as those given, must always be regarded as only
approximately trustworthy in instituting comparisons between either
different diluent gases or different enriching agents.

the gases which are most commonly employed for diluents of acetylene,
under the conditions now being considered, are cannel-coal gas (in
France) and oil-gas (elsewhere). Fowler has made a series of observations
on the illuminating value of mixtures of oil-gas and acetylene. 13.41 per
cent. of acetylene improved the illuminating power of oil-gas from 43 to
49 candles. Thirty-nine-candle-power oil-gas had its illuminating power
raised to about 60 candles by an admixture of 20 per cent. of acetylene,
to about 80 candles by 40 per cent. of acetylene, and to about 110
candles by 60 per cent. of acetylene. The difficulty of employing
mixtures fairly rich in acetylene, or pure acetylene, for railway-
carriage lighting, lies in the poor efficiency of the small burners which
yield from such rich gas a light of 15 to 20 candle-power, such as is
suitable for the purpose. For the lighting of railway carriages it is
seldom deemed necessary to have a flame of more than 20 candle-power, and
it is somewhat difficult to obtain such a flame from oil-gas mixtures
rich in acetylene, unless the illuminative value of the gas is wasted to
a considerable extent. According to Bunte, 15 volumes of coal-gas, 8
volumes of German oil-gas, and 1.5 volumes of acetylene all yield an
equal amount of light; from which it follows that 1 volume of acetylene
is equivalent to 5.3 volumes of German oil-gas.

A lengthy series of experiments upon the illuminating power of mixtures
of oil-gas and acetylene in proportions ranging between 10 and 50 per
cent. of the latter, consumed in different burners and at different
pressures, has been carried out by Borck, of the German State Railway
Department. The figures show that per unit of volume such mixtures may
give anything up to 6.75 times the light evolved by pure oil-gas; but
that the latent illuminating power of the acetylene is less
advantageously developed if too much of it is employed. As 20 per cent.
of acetylene is the highest proportion which may be legally added to oil-
gas in this country, Borck's results for that mixture may be studied:

| | | | | | | |
| | | | | | | Propor- |
| | | | Consump- | | Consump- | tionate |
| Kind of | No. of | Pres- | tion per | Candle- | tion per | Illum- |
| Burner. | Burner | sure. | Hour. | Power. | Candle- | inating |
| | | mm. | Litres. | | Hour. | Power |
| | | | | | Litres. | to Pure |
| | | | | | | Oil-Gas.|
| | | | | | | |
| Bray | 00 | 42 | 82 | 56.2 | 1.15 | 3.38 |
| " | 000 | 35 | 54 | 28.3 | 1.91 | 4.92 |
| " | 0000 | 35 | 43.3 | 16 | 2.71 | 4.90 |
| Oil-gas | | | | | | |
| burner | 15 | 24 | 21 | 7.25 | 2.89 | 4.53 |
| " " | 30 | 15 | 22 | 10.5 | 2.09 | 3.57 |
| " " | 40 | 16 | 33.5 | 20.2 | 1.65 | 3.01 |
| " " | 60 | 33 | 73 | 45.2 | 1.62 | 3.37 |
| |
| The oil-gas from which this mixture was prepared showing: |
| |
| Bray | 00 | 34 | 73.5 | 16.6 | 4.42 | ... |
| " | 000 | 30 | 48 | 6.89 | 6.96 | ... |
| " | 0000 | 28 | 39 | 3.26 | 11.6 | ... |
| Oil-gas | | | | | | |
| burner | 15 | 21 | 19 | 1.6 | 11.8 | ... |
| " " | 30 | 14 | 21.5 | 2.94 | 7.31 | ... |
| " " | 40 | 15 | 33 | 6.7 | 4.92 | ... |
| " " | 60 | 25 | 60 | 13.4 | 4.40 | ... |

It will be seen that the original oil-gas, when compressed to 10
atmospheres, gave a light of 1 candle-hour for an average consumption of
7.66 litres in the Bray burners, and for a consumption of 7.11 litres in
the ordinary German oil-gas jets; while the mixture containing 20 per
cent. of acetylene evolved the same amount of light for a consumption of
2.02 litres in Bray burners, or of 2.06 litres in the oil-gas jets.
Again, taking No. 40 as the most popular and useful size of burner, 1
volume of acetylene oil-gas may be said to be equal to 3 volumes of
simple oil-gas, which is the value assigned to the mixture by the German
Government officials, who, at the prices ruling there, hold the mixture
to be twice as expensive as plain oil-gas per unit of volume, which means
that for a given outlay 50 per cent. more light may be obtained from
acetylene oil-gas than from oil-gas alone.

This comparison of cost is not applicable, as it stands, to compressed
oil-gas, with and without enrichment by acetylene, in this country, owing
to the oils from which oil-gas is made being much cheaper and of better
quality here than in Germany, where a heavy duty is imposed on imported
petroleum. Oil-gas as made from Scotch and other good quality gas-oil in
this country, usually has, after compression, an illuminating duty of
about 8 candles per cubic foot, which is about double that of the
compressed German oil-gas as examined by Borck.

Hence the following table, containing a summary of results obtained by H.
Fowler with compressed oil-gas, as used on English railways, must be
accepted rather than the foregoing, in so far as conditions prevailing in
this country are concerned. It likewise refers to a mixture of oil-gas
and acetylene containing 20 per cent. of acetylene.

| | | | | | |
| | | | | | Ratio of |
| | |Consumption| |Candles per| Illuminating |
| Burner. |Pressure.| per Hour. |Candle| Cubic Foot| Power to that |
| | Inches. |Cubic Feet.|Power.| per Hour. |of Oil-gas [1] |
| | | | | | in the same |
| | | | | | Burner. |
| | | | | | |
| Oil-gas . . | 0.7 | 0.98 | 12.5 | 12.72 | 1.65 |
| Bray 000 . | 0.7 | 1.17 | 14.4 | 12.30 | 1.57 |
| " 0000 . | 0.7 | 0.97 | 10.4 | 10.74 | 1.41 |
| " 00000 | 0.7 | 0.78 | 5.6 | 7.16 | 1.08 |
| " 000000 | 0.7 | 0.55 | 1.9 | 3.52 | 1.14 |

[Footnote 1: Data relating to the relative pecuniary values of acetylene
(carburetted or not), coal-gas, paraffin, and electricity as heating or
illuminating agents, are frequently presented to British readers after
simple recalculation into English equivalents of the figures which obtain
in France and Germany. Such a method of procedure is utterly incorrect,
as it ignores the higher prices of coal, coal-gas, and especially
petroleum products on the Continent of Europe, which arise partly from
geographical, but mainly from political causes.]

The mixture was tried also at higher pressures in the same burners, but
with less favourable results in regard to the duty realised. The oil-gas
was also tried at various pressures, and the most favourable result is
taken for computing the ratio in the last column. It is evident from this
table that 1 volume of this acetylene-oil-gas mixture is equal at the
most to 1.65 volume of the simple oil-gas. Whether the mixture will prove
cheaper under particular conditions must depend on the relative prices of
gas-oil and calcium carbide at the works where the gas is made and
compressed. At the prevailing prices in most parts of Britain, simple
oil-gas is slightly cheaper, but an appreciable rise in the price of gas-
oil would render the mixture with acetylene the cheaper illuminant. The
fact remains, however, that per unit weight or volume of cylinder into
which the gas is compressed, acetylene oil-gas evolves a higher candle-
power, or the same candle-power for a longer period, than simple,
unenriched British oil-gas. Latterly, however, the incandescent mantle
has found application for railway-carriage lighting, and poorer
compressed gases have thereby been rendered available. Thus coal-gas, to
which a small proportion of acetylene has been added, may advantageously
displace the richer oil-gas and acetylene mixtures.

Patents have been taken out by Schwander for the preparation of a mixture
of acetylene, air, and vaporised petroleum spirit. A current of naturally
damp, or artificially moistened, air is led over or through a mass of
calcium carbide, whereby the moisture is replaced by an equivalent
quantity of acetylene; and this mixture of acetylene and air is
carburetted by passing it through a vessel of petroleum spirit in the
manner adopted with air-gas. No details as to the composition,
illuminating power, and calorific values of the gas so made have been
published. It would clearly tend to be of highly indefinite constitution
and might range between what would be virtually inferior carburetted
acetylene, and a low-grade air-gas. It is also doubtful whether the
combustion of such gas would not be accompanied by too grave risks to
render the process useful.



There are sundry uses for acetylene, and to some extent for carbide,
which are not included in what has been said in previous chapters of this
book; and to them a few words may be devoted.

In orchards and market gardens enormous damage is frequently done to the
crops by the ravages of caterpillars of numerous species. These
caterpillars cannot be caught by hand, and hitherto it has proved
exceedingly difficult to cope with them. However, when they have changed
into the perfect state, the corresponding butterflies and moths, like
most other winged insects, are strongly attracted by a bright light. As
acetylene can easily be burnt in a portable apparatus, and as the burners
can be supplied with gas at such comparatively high pressure that the
flames are capable of withstanding sharp gusts of wind even when not
protected by glass, the brilliant light given by acetylene forms an
excellent method of destroying the insects before they have had time to
lay their eggs. Two methods of using the light have been tried with
astonishing success: in one a naked flame is supported within some
receptacle, such as a barrel with one end knocked out, the interior of
which is painted heavily with treacle; in the other the flame is
supported over an open dish filled with some cheap heavy oil (or perhaps
treacle would do equally well). In the first case the insects are
attracted by the light and are caught by the adhesive surfaces; in the
second they are attracted and singed, and then drowned in, or caught by,
the liquid. Either a well-made, powerful, vehicular lamp with its bull's-
eye (if any) removed could be used for this purpose, or a portable
generator of any kind might be connected with the burner through a
flexible tube. It is necessary that the lights should be lit just before
dusk when the weather is fine and the nights dark, and for some twenty
evenings in June or July, exactly at the period of the year when the
perfect insects are coming into existence. In some of the vineyards of
Beaujolais, in France, where great havoc has been wrought by the pyralid,
a set of 10-candle-power lamps were put up during July 1901, at distances
of 150 yards apart, using generators containing 6 oz. of carbide, and
dishes filled with water and petroleum 18 or 20 inches in diameter. In
eighteen nights, some twenty lamps being employed, the total catch of
insects was 170,000, or an average of 3200 per lamp per night. At French
prices, the cost is reported to have been 8 centimes per night, or 32
centimes per hectare (2.5 acres). In Germany, where school children are
occasionally paid for destroying noxious moths, two acetylene lamps
burning for twelve evenings succeeded in catching twice as many insects
as the whole juvenile population of a village during August 1902. A
similar process has been recommended for the destruction of the malarial
mosquito, and should prove of great service to mankind in infected
districts. The superiority of acetylene in respect of brilliancy and
portability will at once suggest its employment as the illuminant in the
"light" moth-traps which entomologists use for entrapping moths. In these
traps, the insects, attracted by the light, flutter down panes of glass,
so inclined that ultimate escape is improbable; while they are protected
from injury through contact with the flame by moans of an intervening
sheet of glass.

Methods of spraying with carbide dust have been found useful in treating
mildew in vines; while a process of burying small quantities of carbide
at the roots has proved highly efficacious in exterminating phylloxera in
the French and Spanish vineyards. It was originally believed that the
impurities of the slowly formed acetylene, the phosphine in particular,
acted as toxic agents upon the phylloxera; and therefore carbide
containing an extra amount of decomposable phosphides was specially
manufactured for the vine-growers. But more recently it has been argued,
with some show of reason, that the acetylene itself plays a part in the
process, the effects produced being said to be too great to be ascribed
wholly to the phosphine. It is well known that many hydrocarbon vapours,
such as the vapour of benzene or of naphthalene, have a highly toxic
action on low organisms, and the destructive effect of acetylene on
phylloxera may be akin to this action.

As gaseous acetylene will bear a certain amount of pressure in safety--a
pressure falling somewhat short of one effective atmosphere--and as
pressure naturally rises in a generating apparatus where calcium carbide
reacts with water, it becomes possible to use this pressure as a source
of energy for several purposes. The pressure of the gas may, in fact, be
employed either to force a stream of liquid through a pipe, or to propel
certain mechanism. An apparatus has been constructed in France on the
lines of some portable fire-extinguishing appliances in which the
pressure set up by the evolution of acetylene in a closed space produces
a spray of water charged with lime and gas under the pressure obtaining;
the liquid being thrown over growing vines or other plants in order to
destroy parasitic and other forms of life. The apparatus consists of a
metal cylinder fitted with straps so that it can be carried by man or
beast. At one end it has an attachment for a flexible pipe, at the other
end a perforated basket for carbide introduced and withdrawn through a
"man-hole" that can be tightly closed. The cylinder is filled with water
to a point just below the bottom of the basket when the basket is
uppermost; the carbide charge is then inserted, and the cover fastened
down. As long as the cylinder is carried in the same position, no
reaction between the carbide and the water occurs, and consequently no
pressure arises; but on inverting the vessel, the carbide is wetted, and
acetylene is liberated in the interior. On opening the cock on the outlet
pipe, a stream of liquid issues and may be directed as required. By
charging the cylinder in the first place with a solution of copper
sulphate, the liquid ejected becomes a solution and suspension of copper
and calcium salts and hydroxides, resembling "Bordeaux mixture," and may
be employed as such. In addition, it is saturated with acetylene which
adds to its value as a germicide.

The effective gas pressure set up in a closed generator has also been
employed in Italy to drive a gas-turbine, and so to produce motion. The
plant has been designed for use in lighthouses where acetylene is burnt,
and where a revolving or flashing light is required. The gas outlet from
a suitably arranged generator communicates with the inlet of a gas-
turbine, and the outlet of the turbine is connected to a pipe leading to
the acetylene burners. The motion of the turbine is employed to rotate
screens, coloured glasses, or any desired optical arrangements round the
flames; or, in other situations, periodically to open and close a cock on
the gas-main leading to the burners. In the latter case, a pilot flame
fed separately is always alight, and serves to ignite the gas issuing
from the main burners when the cock is opened.

Another use for acetylene, which is only dependent upon a suitably
lowered price for carbide to become of some importance, consists in the
preparation of a black pigment to replace ordinary lampblack. One method
for this purpose has been elaborated by Hubou. Acetylene is prepared from
carbide smalls or good carbide, according to price, and the gas is pumped
into small steel cylinders to a pressure of 2 atmospheres. An electric
spark is then passed, and the gas, standing at its limit of safety,
immediately dissociates, yielding a quantitative amount of hydrogen and
free carbon. The hydrogen is drawn off, collected in holders, and used
for any convenient purpose; the carbon is withdrawn from the vessel, and
is ready for sale. At present the pigment is much too expensive, at least
in British conditions, to be available in the manufacture of black paint;
but its price would justify its employment in the preparation of the best
grades of printers' ink. One of the authors has examined an average
sample and has found it fully equal in every way to blacks, such as those
termed "spirit blacks," which fetch a price considerably above their real
value. It has a pure black cast of tint, is free from greasy matter, and
can therefore easily be ground into water, or into linseed oil without
interfering with the drying properties of the latter. Acetylene black has
also been tried in calico printing, and has given far better results in
tone and strength than other blacks per unit weight of pigment. It may be
added that the actual yield of pigment from creosote oils, the commonest
raw material for the preparation of lampblack ("vegetable black"), seldom
exceeds 20 or 25 per cent., although the oil itself contains some 80 per
cent, of carbon. The yield from acetylene is clearly about 90 per cent.,
or from calcium carbide nearly 37.5 per cent, of the original weight.

An objection urged against the Hubou process is that only small
quantities of the gas can be treated with the spark at one time; if the
cylinders are too large, it is stated, tarry by-products are formed. A
second method of preparing lampblack (or graphite) from acetylene is that
devised by Frank, and depends on utilising the reactions between carbon
monoxide or dioxide and acetylene or calcium carbide, which have already
been sketched in Chapter VI. When acetylene is employed, the yield is
pure carbon, for the only by-product is water vapour; but if the carbide
process is adopted, the carbon remains mixed with calcium oxide. Possibly
such a material as Frank's carbide process would give, viz., 36 parts by
weight of carbon mixed with 56 parts of quicklime or 60 parts of carbon
mixed with 112 parts of quicklime, might answer the purpose of a pigment
in some black paints where the amount of ash left on ignition is not
subject to specification. Naturally, however, the lime might be washed
away from the carbon by treatment with hydrochloric acid; but the cost of
such a purifying operation would probably render the residual pigment too
expensive to be of much service except (conceivably) in the manufacture
of certain grades of printers' ink, for which purpose it might compete
with the carbon obtainable by the Hubou process already referred to.

Acetylene tetrachloride, or tetrachlorethane, C_2H_2Cl_4, is now produced
for sale as a solvent for chlorine, sulphur, phosphorus, and organic
substances such as fats. It may be obtained by the direct combination of
acetylene and chlorine as explained in Chapter VI., but the liability of
the reaction to take place with explosive violence would preclude the
direct application of it on a commercial scale. Processes free from such
risk have now, however, been devised for the production of
tetrachlorethane. One patented by the Salzbergwerk Neu-Stassfurt consists
in passing acetylene into a mixture of finely divided iron and chloride
of sulphur. The iron acts as a catalytic. The liquid is kept cool, and as
soon as the acetylene passes through unabsorbed, its introduction is
stopped and chlorine is passed in. Acetylene and chlorine are then passed
in alternately until the liquid finally is saturated with acetylene. The
tetrachlorethane, boiling at 147 deg. C., is then distilled off, and the
residual sulphur is reconverted to the chloride for use again in the
process. A similar process in which the chlorine is used in excess is
applicable also to the production of hexachlorethane.

Dependent upon price, again, are several uses for calcium carbide as a
metallurgical or reducing reagent; but as those are uses for carbide only
as distinguished from acetylene, they do not fall within the purview of
the present book.

When discussing, in Chapter III., methods for disposing of the lime
sludge coming from an acetylene generator, it was stated that on occasion
a use could be found for this material. If the carbide has been entirely
decomposed in an apparatus free from overheating, the waste lime is
recovered as a solid mass or as a cream of lime practically pure white in
colour. Sometimes, however, as explained in Chapter II., the lime sludge
is of a bluish grey tint, even in cases where the carbide decomposed was
of good quality and there was no overheating in the generator. Such
discoloration is of little moment for most of the uses to which the
sludge may be put. The residue withdrawn from a carbide-to-water
generator is usually quite fluid; but when allowed to rest in a suitable
pit or tank, it settles down to a semi-solid or pasty mass which contains
on a rough average 47 per cent. of water and 53 per cent. of solid
matter, the amount of lime present, calculated as calcium oxide, being
about 40 per cent. Since 64 parts by weight of pure calcium carbide yield
74 parts of dry calcium hydroxide, it may be said that 1 part of ordinary
commercial carbide should yield approximately 1.1 parts of dry residue,
or 2.1 parts of a sludge containing 47 per cent. of moisture; and sludge
of this character has been stated by Vogel to weigh about 22.5 cwt. per
cubic yard.

Experience has shown that those pasty carbide residues can be employed
very satisfactorily, and to the best advantage from the maker's point of
view, by builders and decorators for the preparation of ordinary mortar
or lime-wash. The mortar made from acetylene lime has been found equal in
strength and other properties to mortar compounded from fresh slaked
lime; while the distemper prepared by diluting the sludge has been used
most successfully in all places where a lime-wash is required,
_e.g._, on fruit-trees, on cattle-pens, farm-buildings, factories,
and the "offices" of a residence. Many of the village installations
abroad sell their sludge to builders for the above-mentioned purposes at
such a price that their revenue accounts are materially benefited by the
additional income. The sludge is also found serviceable for softening the
feed-water of steam boilers by the common liming process; although it has
been stated that the material contains certain impurities--notably "fatty
matter"--which becomes hydrolysed by the steam, yielding fatty acids that
act corrosively upon the boiler-plates. This assertion would appear to
require substantiation, but a patent has been taken out for a process of
drying the sludge at a temperature of 150 deg. to 200 deg. C. in order to
remove the harmful matter by the action of the steam evolved. So purified,
it is claimed, the lime becomes fit for treating any hard potable or
boiler-feed water. It is very doubtful, however, whether the intrinsic value
of acetylene lime is such in comparison with the price of fresh lime that,
with whatever object in view, it would bear the cost of any method of
artificial drying if obtained from the generators in a pasty state.

When, on the other hand, the residue is naturally dry, or nearly so, it
is exactly equal to an equivalent quantity of quick or slaked lime as a
dressing for soil. In this last connexion, however, it must be remembered
that only certain soils are improved by an addition of lime in any shape,
and therefore carbide residues must not be used blindly; but if analysis
indicates that a particular plot of ground would derive benefit from an
application of lime, acetylene lime is precisely as good as any other
description. Naturally a residue containing unspent carbide, or
contaminated with tarry matter, is essentially valueless (except as
mentioned below); while it must not be forgotten that a solid residue if
it is exposed to air, or a pasty residue if not kept under water, will
lose many of its useful properties, because it will be partially
converted into calcium carbonate or chalk.

Nevertheless, in some respects, the residue from a good acetylene
generator is a more valuable material, agriculturally speaking, than pure
lime. It contains a certain amount of sulphur, &c., and it therefore
somewhat resembles the spent or gas lime of the coal-gas industry. This
sulphur, together, no doubt, with the traces of acetylene clinging to it,
renders the residue a valuable material for killing the worms and vermin
which tend to infest heavily manured and under-cultivated soil. Acetylene
lime has been found efficacious in exterminating the "finger-and-toe" of
carrots, the "peach-curl" of peach-trees, and in preventing cabbages from
being "clubbed." It may be applied to the ground alone, or after
admixture with some soil or stable manure. The residue may also be
employed, either alone or mixed with some agglomerate, in the
construction of garden paths and the like.

If the residues are suitably diluted with water and boiled with (say)
twice their original weight of flowers of sulphur, the product consists
of a mixture of various compounds of calcium and sulphur, or calcium
sulphides--which remain partly in solution and partly in the solid state.
This material, used either as a liquid spray or as a moist dressing, has
been said to prove a useful garden insecticide and weed-killer.

There are also numerous applications of the acetylene light, each of much
value, but involving no new principle which need be noticed. The light is
so actinic, or rich in rays acting upon silver salts, that it is
peculiarly useful to the photographer, either for portraiture or for his
various positive printing operations. Acetylene is very convenient for
optical lantern work on the small scale, or where the oxy-hydrogen or
oxy-coal-gas light cannot be used. Its intensity and small size make its
self-luminous flame preferable on optical grounds to the oil-lamp or the
coal-gas mantle; but the illuminating surface is nevertheless too large
to give the best results behind such condensers as have been carefully
worked to suit a source of light scarcely exceeding the dimensions of a
point. For lantern displays on very large screens, or for the projection
of a powerful beam of light to great distances in one direction (as in
night signalling, &c.), the acetylene blowpipe fed with pure oxygen, or
with air containing more than its normal proportion of oxygen, which is
discussed in Chapter IX., is specially valuable, more particularly if the
ordinary cylinder of lime is replaced by one of magnesia, zirconia, or
other highly refractory oxide.



It will be apparent from what has been said in past chapters that the
construction of a satisfactory generator for portable purposes must be a
problem of considerable complexity. A fixed acetylene installation tends
to work the more smoothly, and the gas evolved therefrom to burn the more
pleasantly, the more technically perfect the various subsidiary items of
the plant are; that is to say, the more thoroughly the acetylene is
purified, dried, and delivered at a strictly constant pressure to the
burners and stoves. Moreover, the efficient behaviour of the generator
itself will depend more upon the mechanical excellence and solidity of
its construction than (with one or two exceptions) upon the precise
system to which it belongs. And, lastly, the installation will, broadly
speaking, work the better, the larger the holder is in proportion to the
demands ever made upon it; while that holder will perform the whole duty
of a gasholder more effectually if it belongs to the rising variety than
if it is a displacement holder. All these requirements of a good
acetylene apparatus have to be sacrificed to a greater or less extent in
portable generators; and since the sacrifice becomes more serious as the
generator is made smaller and lighter in weight, it may be said in
general terms that the smaller a portable (or, indeed, other) acetylene
apparatus is, the less complete or permanent satisfaction will it give
its user. Again, small portable apparatus are only needed to develop
intensities of light insignificant in comparison with those which may
easily be won from acetylene on a larger scale; they are therefore fitted
with smaller burners, and those burners are not merely small in terms of
consumption and illuminating power, but not infrequently are very badly
constructed, and are relatively deficient in economy or duty. Thus any
comparisons which may be made on lines similar to those adopted in
Chapter I., or between unit weights, volumes, or monetary equivalents of
calcium carbide, paraffin, candles, and colza oil, become utterly
incorrect if the carbide is only decomposed in a small portable generator
fitted with an inefficient jet; first, because the latent illuminating
power of the acetylene evolved is largely wasted; secondly, because any
gas produced over and above that capable of instant combustion must be
blown off from a vent-pipe; and thirdly, because the carbide itself tends
to be imperfectly decomposed, either through a defect in the construction
of the lamp, or through the brief and interrupted requirements of the

In several important respects portable acetylene apparatus may be divided
into two classes from a practical point of view. There is the portable
table or stand lamp intended for use in an occupied room, and there is
the hand or supported lamp intended for the illumination of vehicles or
open-air spaces. Economy apart, no difficulty arises from imperfect
combustion or escape of unburnt gas from an outdoor lamp, but in a room
the presence of unburnt acetylene must always be offensive even if it is
not dangerous; while the combustion products of the impurities--and in a
portable generator acetylene cannot be chemically purified--are highly
objectionable. It is simply a matter of good design to render any form of
portable apparatus safe against explosion (employment of proper carbide
being assumed), for one or more vent-pipes can always be inserted in the
proper places; but from an indoor lamp those vent-pipes cannot be made to
discharge into a place of safety, while, as stated before, a generator in
which the vent-pipes come into action with any frequency is but an
extravagant piece of apparatus for the decomposition of so costly a
material as calcium carbide. Looked at from one aspect the holder of a
fixed apparatus is merely an economical substitute for the wasteful vent-
pipe, because it is a place in which acetylene can be held in reserve
whenever the make exceeds the consumption in speed. It is perhaps
possible to conceive of a large table acetylene lamp fitted with a water-
sealed rising holder; but for vehicular purposes the displacement holder
is practically the only one available, and in small apparatus it becomes
too minute in size to be of much service as a store for the gas produced
by after-generation. Other forms of holder have been suggested by
inventors, such as a collapsible bag of india-rubber or the like; but
rubber is too porous, weak, and perishable a material to be altogether
suitable. If it is possible, by bringing carbide and water into mutual
contact in predetermined quantities, to produce gas at a uniform rate,
and at one which corresponds with the requirements of the burner, in a
small apparatus--and experience has shown it to be possible within
moderately satisfactory limits--it is manifest that the holder is only
needed to take up the gas of after-generation; and in Chapters II. and
III. it was pointed out that after-generation only occurs when water is
brought into contact with an excess of carbide. If, then, the opposite
system of construction is adopted, and carbide is fed into water
mechanically, no after-generation can take place; and provided the make
of gas can be controlled in a small carbide-feed generator as accurately
as is possible in a small water-to-carbide generator, the carbide-feed
principle will exhibit even greater advantages in portable apparatus than
it does in plant of domestic size. Naturally almost every variety of
carbide-feeding gear, especially when small, requires or prefers
granulated (or granulated and "treated") carbide; and granulated carbide
must inevitably be considerably more expensive per unit of light evolved
than the large material, but probably in the application to which the
average portable acetylene apparatus is likely to be put, strict economy
is not of first consequence. In portable acetylene generators of the
carbide-feed type, the supply is generally governed by the movements of a
mushroom-headed or conical valve at the mouth of a conical carbide
vessel; such movements occurring in sympathy with the alterations in
level of the water in the decomposing chamber, which is essentially a
small displacement holder also, or being produced by the contraction of a
flexible chamber through which the gas passes on its way to the burner.
So far as it is safe to speak definitely on a matter of this kind, the
carbide-feed device appears to work satisfactorily in a stationary
(_e.g._, table) lamp; but it is highly questionable whether it could
be applied to a vehicular apparatus exposed to any sensible amount of
vibration. The device is satisfactory on the table of an occupied room so
far, be it understood, as any small portable generators can be: it has no
holder, but since no after-generation occurs, no holder is needed; still
the combustion products contaminate the room with all the sulphur and
phosphorus of the crude acetylene.

For vehicular lamps, and probably for hand lanterns, the water-to-carbide
system has practically no alternative (among actual generators), and
safety and convenience have to be gained at the expense of the carbide.
In such apparatus the supply of water is usually controlled ultimately by
pressure, though a hand-operated needle-valve is frequently put on the
water tube. The water actually reaches the carbide either by dropping
from a jet, by passing along, upwards or downwards, a "wick" such as is
used in oil-lamps, or by percolating through a mass of porous material
like felt. The carbide is held in a chamber closed except at the gas exit
to the burner and at the inlet from the water reservoir: so that if gas
is produced more rapidly than the burner takes it, more water is
prevented from entering, or the water already present is driven backwards
out of the decomposing chamber into some adjoining receptacle. It is
impossible to describe in detail all the lamps which have been
constructed or proposed for vehicular use; and therefore the subject must
be approached in general terms, discussing simply the principles involved
in the design of a safe portable generator.

In all portable apparatus, and indeed in generators of larger dimensions,
the decomposing chamber must be so constructed that it can never, even by
wrong manipulation, be sealed hermetically against the atmosphere. If
there is a cock on the water inlet tube which is capable of being
completely shut, there must be no cock between the decomposing chamber
and the burner. If there is a cock between the carbide vessel and the
burner, the water inlet tube must only be closed by the water, being
water-sealed, in fact, so that if pressure rises among the carbide the
surplus gas may blow the seal or bubble through the water in the
reservoir. If the water-supply is mainly controlled by a needle-valve, it
is useful to connect the burner with the carbide vessel through a short
length of rubber tube; and if this plan is adopted, a cock can, if
desired, be put close to the burner. The rubber should not be allowed to
form a bend hanging down, or water vapour, &c., may condense and
extinguish the flame. In any case there should be a steady fall from the
burner to the decomposing chamber, or to some separate catch-pit for the
products of condensation. Much of the success attainable with small
generators will depend on the water used. If it is contaminated with
undissolved matter, the dirt will eventually block the fine orifices,
especially the needle-valve, or will choke the pores of the wick or the
felt pad. If the water contains an appreciable amount of "temporary
hardness," and if it becomes heated much in the lamp, fur will be
deposited sooner or later, and will obviously give trouble. Where the
water reservoir is at the upper part of the lamp, and the liquid is
exposed to the heat of the flame, fur will appear quickly if the water is
hard. Considerable benefit would accrue to the user of a portable lamp by
the employment of rain water filtered, if necessary, through fabric or
paper. The danger of freezing in very severe weather may be prevented by
the use of calcium chloride, or preferably, perhaps, methylated spirit in
the water (_cf._ Chapter III., p. 92). The disfavour with which
cycle and motor acetylene lamps are frequently regarded by nocturnal
travellers, other than the users thereof, is due to thoughtless design in
the optical part of such lamps, and is no argument against the employment
of acetylene. By proper shading or deflection of the rays, the eyes of
human beings and horses can be sufficiently protected from the glare, and
the whole of the illumination concentrated more perfectly on the road
surface and the lower part of approaching objects--a beam of light never
reaching a height of 5 feet above the ground is all that is needed to
satisfy all parties.

As the size of the generator rises, conditions naturally become more
suited to the construction of a satisfactory apparatus; until generators
intended to supply light to the whole of (say) a railway carriage, or the
head and cab lamps of a locomotive, or for the outside and inside
lighting of an omnibus are essentially generators of domestic dimensions
somewhat altered in internal construction to withstand vibration and
agitation. As a rule there is plenty of space at the side of a locomotive
to carry a generator fitted with a displacement holder of sufficient
size, which is made tall rather than wide, to prevent the water moving
about more than necessary. From the boiler, too, steam can be supplied to
a coil to keep the liquid from freezing in severe weather. Such apparatus
need not be described at length, for they can be, and are, made on lines
resembling those of domestic generators, though more compactly, and
having always a governor to give a constant pressure. For carriage
lighting any ordinary type of generator, preferably, perhaps, fitted with
a displacement holder, can be erected either in each corridor carriage,
or in a brake van at the end of the train. Purifiers may be added, if
desired, to save the burners from corrosion; but the consumption of
unpurified gas will seldom be attended by hygienic disadvantages, because
the burners will be contained in closed lamps, ventilating into the
outside air. The generator, also, may conveniently be so constructed that
it is fed with carbide from above the roof, and emptied of lime sludge
from below the floor of the vehicle. It can hardly be said that the use
of acetylene generated on board adds a sensible risk in case of
collision. In the event of a subsequent fire, the gas in the generator
would burn, but not explode; but in view of the greater illuminating
power per unit volume of carbide than per equal volume of compressed oil-
gas, a portable acetylene generator should be somewhat less objectionable
than broken cylinders of oil-gas if a fire should follow a railway
accident of the usual kind. More particularly by the use of "cartridges"
of carbide, a railway carriage generator can be constructed of sufficient
capacity to afford light for a long journey, or even a double journey, so
that attention would be only required (in the ordinary way) at one end of
the line.

Passing on from the generators used for the lighting of vehicles and for
portable lamps for indoor lighting to the considerably larger portable
generators now constructed for the supply of acetylene for welding
purposes and for "flare" lamps, it will be evident that they may embody
most or all of the points which are essential to the proper working of a
fixed generator for the supply of a small establishment. The holder will
generally be of the displacement type, but some of these larger portable
generators are equipped with a rising holder. The generators are,
naturally, automatic in action, but may be either of the water-to-carbide
or carbide-to-water type--the latter being preferable in the larger sizes
intended for use with the oxy-acetylene blow-pipe for welding, &c., for
which use a relatively large though intermittent supply of acetylene is
called for. The apparatus is either carried by means of handles or poles
attached to it, or is mounted on a wheelbarrow or truck for convenience
of transport to the place where it is to be used. The so called "flare"
lamps, which are high power burners mounted, with or without a reflector,
above a portable generator, are extremely useful for lighting open spaces
where work has to be carried on temporarily after nightfall, and are
rapidly displacing oil-flares of the Lucigen type for such purposes.

The use of "cartridges" of calcium carbide has already been briefly
referred to in Chapters II. and III. These cartridges are usually either
receptacles of thin sheet-metal, say tin plate, or packages of carbide
wrapped up in grease proof paper or the like. If of metal, they may have
a lid which is detached or perforated before they are put into the
generator, or the generator (when automatic and of domestic size) may be
so arranged that a cartridge is punctured in one or more places whenever
more gas is required. If wrapped in paper, the cartridges may be dropped
into water by an automatic generator at the proper times, the liquid then
loosening the gum and so gaining access to the interior; or one spot may
be covered by a drape of porous material (felt) only, through which the
water penetrates slowly. The substance inside the cartridge may be
ordinary, granulated, or "treated" carbide. Cartridges or "sticks" of
carbide are also made without wrappings, either by moistening powdered
carbide with oil and compressing the whole into moulds, or by compressing
dry carbide dust and immersing the sticks in oil or molten grease. The
former process is said to cause the carbide to take up too much oil, so
that sticks made by the second method are reputed preferable. All these
cartridges have the advantage over common carbide of being more permanent
in damp air, of being symmetrical in shape, of decomposing at a known
speed, and of liberating acetylene in known quantity; but evidently they
are more expensive, owing to the cost of preparing them, &c. They may be
made more cheaply from the dust produced in the braking of carbide, but
in that case the yield of gas will be relatively low.

It is manifest that, where space is to spare, purifiers containing the
materials mentioned in Chapter V. can be added to any portable acetylene
apparatus, provided also that the extra weight is not prohibitive. Cycle
lamps and motor lamps must burn an unpurified gas unpurified from
phosphorus and sulphur; but it is always good and advisable to filter the
acetylene from dust by a plug of cotton wool or the like, in order to
keep the burners as clear as may be. A burner with a screwed needle for
cleaning is always advantageous. Formerly the burners used on portable
acetylene lamps were usually of the single jet or rat-tail, or the union
jet or fish tail type, and exhibited in an intensified form, on account
of their small orifices, all the faults of these types of burners for the
consumption of acetylene (see Chapter VIII.). Now, however, there are
numerous special burners adapted for use in acetylene cycle and motor
lamps, &c., and many of these are of the impinging jet type, and some
have steatite heads to prevent distortion by the heat. One such cycle-
lamp burner, as sold in England by L. Wiener, of Fore Street, London, is
shown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII.) is
made in small sizes (6, 8 and 10 litres per hour) for use in vehicular
lamps, under the name of the "Konette," by Falk, Stadelmann and Co.,
Ltd., of London, who also make a number of other small impinging jet
burners. A single jet injector burner on the "Phos" principle is made in
small sizes by the Phos Co., of London, specially for use in lamps on

[Illustration: FIG. 21.--CYCLE-LAMP BURNER NO. 96042A.]

Nevertheless, although satisfactory medium-sized vehicular lamps for the
generation of acetylene have been constructed, the best way of using
acetylene for all such employments as these is to carry it ready made in
a state of compression. For railway purposes, where an oil-gas plant is
in existence, and where it is merely desired to obtain a somewhat
brighter light, the oil-gas may be enriched with 20 per cent. of
acetylene, and the mixed gas pumped into the same cylinders to a pressure
of 10 atmospheres, as mentioned in Chapter XI.; the only alteration
necessary being the substitution of suitable small burners for the common
oil-gas jets. As far as the plant is concerned, all that is required is a
good acetylene generator, purifier, and holder from which the acetylene
can be drawn or forced through a meter into a larger storage holder, the
meter being connected by gearing with another meter on the pipe leading
from the oil-gas holder to the common holder, so that the necessary
proportions of the two gases shall be introduced into the common holder
simultaneously. From this final holder the enriched gas will be pumped
into the cylinders or into a storage cylinder, by means of a thoroughly
cooled pump, so that the heat set free by the compression may be safely

Whenever still better light is required in railway carriages, as also for
the illumination of large, constantly used vehicles, such as omnibuses,
the acetone process (_cf._ Chapter XI.) exhibits notable advantages.
The light so obtained is the light of neat acetylene, but the gas is
acetylene having an upper limit of explosibility much lower than usual
because of the vapour of acetone in it. In all other respects the
presence of the acetone will be unnoticeable, for it is a fairly pure
organic chemical body, which burns in the flame completely to carbon
dioxide and water, exactly as acetylene itself does. If the acetylene is
merely compressed into porous matter without acetone, the gas burnt is
acetylene simply; but per unit of volume or weight the cylinders will not
be capable of developing so much light.

In the United States, at least one railway system (The Great Northern)
has a number of its passenger coaches lighted by means of plain acetylene
carried in a state of compression in cylinders without porous matter. The
gas is generated, filtered from dust, and stored in an ordinary rising
holder at a factory alongside the line; being drawn from this holder
through a drier to extract moisture, and through a safety device, by a
pump which, in three stages, compresses the acetylene into large storage
reservoirs. The safety device consists of a heavy steel cylinder filled
with some porous substance which, like the similar material of the
acetone cylinders, prevents any danger of the acetylene contained in the
water-sealed holder being implicated in an explosion starting backwards
from the compression, by extinguishing any spark which might be produced
there. The plant on the trains comprises a suitable number of cylinders,
filled by contact with the large stores of gas to a pressure of 10
atmospheres, pipes of fusible metal communicating with the lamps, and
ordinary half-foot acetylene burners. The cylinders are provided with
fusible plugs, so that, in the event of a fire, they and the service-
pipes would melt, allowing the gas to escape freely and burn in the air,
instead of exploding or dissociating explosively within the cylinders
should the latter be heated by any burning woodwork or the like. It is
stated that this plan of using acetylene enables a quantity of gas to be
carried under each coach which is sufficient for a run of from 53 to 70
hours' duration, or of over 3600 miles; that is to say, enables the
train, in the conditions obtaining on the line in question, to make a
complete "round trip" without exhaustion of its store of artificial
light. The system has been in operation for some years, and appears to
have been so carefully managed that no accident has arisen; but it is
clear that elements of danger are present which are eliminated when the
cylinders are loaded with porous matter and acetone. The use of a similar
system of compressed acetylene train lighting in South America has been
attended with a disastrous explosion, involving loss of life.

It may safely be said that the acetone system, or less conveniently
perhaps the mere compression into porous matter, is the best to adopt for
the table-lamp which is to be used in occupied rooms Small cylinders of
such shapes as to form an elegant base for a table-lamp on more or less
conventional lines would be easy to make. They would be perfectly safe to
handle. If accidentally or wilfully upset, no harm would arise. By
deliberate ill-treatment they might be burst, or the gas-pipe fractured
below the reducing valve, so that gas would escape under pressure for a
time; but short of this they would be as devoid of extra clangor in times
of fire as the candle or the coal-gas burner. Moreover, they would only
contaminate the air with carbon dioxide and water vapour, for the gas is
purified before compression; and modern investigations have conclusively
demonstrated that the ill effects produced in the air of an imperfectly
ventilated room by the extravagant consumption of coal-gas depend on the
accumulation of the combustion products of the sulphur in the gas rather
than upon the carbon dioxide set free.

One particular application of the portable acetylene apparatus is of
special interest. As calcium carbide evolves an inflammable gas when it
merely comes into contact with water, it becomes possible to throw into
the sea or river, by hand or by ejection from a mortar, a species of bomb
or portable generator which is capable of emitting a powerful beam of
light if only facilities are present for inflaming the acetylene
generated; and it is quite easy so to arrange the interior of such
apparatus that they can be kept ready for instant use for long periods of
time without sensible deterioration, and that they can be recharged after
employment. Three methods of firing the gas have been proposed. In one
the shock or contact with the water brings a small electric battery into
play which produces a spark between two terminals projecting across the
burner orifice; in the second, a cap at the head of the generator
contains a small quantity of metallic potassium, which decomposes water
with such energy that the hydrogen liberated catches fire; and in the
third a similar cap is filled with the necessary quantity of calcium
phosphide, or the "carbophosphide of calcium" mentioned in Chapter XI.,
which yields a flame by the immediate ignition of the liquid phosphine
produced on the attack of water. During the two or three seconds consumed
in the production of the spark or pilot flame, the water is penetrating
the main charge of calcium carbide in the interior of the apparatus,
until the whole is ready to give a bright light for a time limited only
by the capacity of the generator. It is obvious that such apparatus may
be of much service at sea: they may be thrown overboard to illuminate
separate lifebuoys in case of accident, or be attached to the lifebuoys
they are required to illuminate, or be used as lifebuoys themselves if
fitted with suitable chains or ropes; they may be shot ahead to
illuminate a difficult channel, or to render an enemy visible in time of
war. Several such apparatus have already been constructed and severely
tested; they appear to give every satisfaction. They are, of course, so
weighted that the burner floats vertically, while buoyancy is obtained
partly by the gas evolved, and partly by a hollow portion of the
structure containing air. Cartridges of carbide and caps yielding a self-
inflammable gas can be carried on board ship, by means of which the
torches or lifebuoys may be renewed after service in a few minutes' time.



The sale and purchase of calcium carbide in this country will, under
existing conditions, usually be conducted in conformity with the set of
regulations issued by the British Acetylene Association, of which a copy,
revised to date, is given below:


1. The carbide shall be guaranteed by the seller to yield, when broken
to standard size, _i.e._, in lumps varying from 1 to 2-1/2 inches or
larger, not less than 4.8 cubic feet per lb., at a barometric pressure of
30 inches and temperature of 60 deg. Fahr. (15.55 deg. Centigrade). The
actual gas yield shall be deemed to be the gas yield ascertained by the
analyst, plus 5 per cent.

"Carbide yielding less than 4.8 cubic feet in the sizes given above shall
be paid for in proportion to the gas yield, _i.e._, the price to be
paid shall bear the same relation to the contract price as the gas yield
bears to 4.8 cubic feet per lb.

"2. The customer shall have the right to refuse to take carbide yielding
in the sizes mentioned above less than 4.2 cubic foot, per lb., and it
shall lie, in case of refusal and as from the date of the result, of the
analysis being made known to either party, at the risk and expense of the

"3. The carbide shall not contain higher figures of impurities than shall
from time to time be fixed by the Association.

"4. No guarantee shall be given for lots of less than 3 cwt., or for
carbide crushed to smaller than the above sizes.

"5. In case of dispute as to quality, either the buyer or the seller
shall have the right to have one unopened drum per ton of carbide, or
part of a ton, sent for examination to one of the analysts appointed by
the Association, and the result of the examination shall be held to apply
to the whole of the consignment to which the drum belonged.
"6. A latitude of 5 per cent, shall be allowed for analysis; consequently
differences of 5 per cent. above or below the yields mentioned in 1 and 2
shall not be taken into consideration.

"7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent.,
the carriage of the carbide to and from the place of analysis and the
cost of the analysis shall be paid for by the seller. Should the yield be
more than 4.8 cubic feet less 5 per cent., the carriage and costs of
analysis shall be borne by the buyer, who, in addition, shall pay an
increase of price for the carbide proportionate to the gas yield above
4.8 cubic feet plus 5 per cent.

"8. Carbide of 1 inch mesh and above shall not contain more than 5 per
cent. of dust, such dust to be defined as carbide capable of passing
through a mesh of one-sixteenth of an inch.

"9. The seller shall not be responsible for deterioration of quality
caused by railway carriage in the United Kingdom, unless he has sold
including carriage to the destination indicated by the buyer.

"10. Carbide destined for export shall, in case the buyer desires to have
it tested, be sampled at the port of shipment, and the guarantee shall
cease after shipment.

"11. The analyst shall take a sample of not less than 1 lb. each from the
top, centre, and bottom of the drum. The carbide shall be carefully
broken up into small pieces, due care being taken to avoid exposure to
the air as much as possible, carefully screened and tested for gas yield
by decomposing it in water, previously thoroughly saturated by exposure
to acetylene for a period of not less than 48 hours.

"12. Carbide which, when properly decomposed, yields acetylene containing
from all phosphorus compounds therein more than .05 per cent. by volume
of phosphoretted hydrogen, may be refused by the buyer, and any carbide
found to contain more than this figure, with a latitude of .01 per cent.
for the analysis, shall lie at the risk and expense of the seller in the
manner described in paragraph 2.

"The rules mentioned in paragraph 7 shall apply as regards the carriage
and costs of analysis; in other words, the buyer shall pay these costs if
the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if
the figure is above 0.05 per cent. plus 0.01 per cent.

"The sampling shall take place in the manner prescribed in paragraphs 5
and 11, and the analytical examination shall be effected in the manner
prescribed by the Association and obtainable upon application to the

* * * * *

The following is a translation of the corresponding rules issued by the
German Acetylene Association (_Der Deutsche Acetylenverein_) in
regard to business dealings in calcium carbide, as put into force on
April 1, 1909:



"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of
carbide in packages containing about 100 kilogrammes.

"By packages containing about 100 kilogrammes are meant packages
containing within 10 per cent. above or below that weight.

"The carbide shall be packed in gas- and water-tight vessels of sheet-
iron of the strength indicated in the prescriptions of the carrying

"The prices for other descriptions of packing must be specially stated.

"_Place of Delivery_.

"For consignment for export, the last European shipping port shall be
taken as the place of delivery.


"Commercial carbide shall be of such quality that in the usual lumps of
15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of
at least 300 litres at 15 deg. C. and 760 mm. pressure of crude acetylene
per kilogramme for each consignment (= 4.81 cubic feet at 60 deg. F. and
30 inches per lb.). A margin of 2 per cent. shall be allowed for the
analysis. Carbide which yields less than 300 litres per kilogramme, but
not less than 270 litres (= 4.33 cubic feet) of crude acetylene per
kilogramme (with the above-stated 2 per cent. margin for analysis) must
be accepted by the buyer. The latter, however, is entitled to make a
proportionate deduction from the price and also to deduct the increased
freight charges to the destination or, if the latter is not settled at
the time when the transaction is completed, to the place of delivery.
Carbide which yields less than 270 litres of crude acetylene per
kilogramme need not be accepted.

"Carbide must not contain more than 5 per cent. of dust. By dust is to be
understood all which passes through a screen of 1 mm. (0.04 inch) square,
clear size of holes.

"Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and
intermediate sizes) must yield on the average for each delivery at least
270 litres at 15 deg. C. and 760 mm. pressure of crude acetylene per
kilogramme (= 4.33 cubic feet at 60 deg. F. and 30 inches per lb.) A margin
of 2 per cent. shall be allowed for the analysis. Small carbide of from 4
to 15 mm. in size (and intermediate sizes) which yields less than 270
litres but not less than 250 litres (= 4.01 cubic feet per lb.) of crude
acetylene per kilogramme (with the above-stated 2 per cent. margin for
analysis) must be accepted by the buyer. The latter, however, is entitled
to make a proportionate deduction from the price and also to deduct the
increased freight charges to the destination or, if the latter is not
settled at the time when the transaction is completed, to the place of
delivery. Small carbide of from 4 to 15 mm. in size (and intermediate
sizes) which yields less than 250 litres per kilogramme need not be

"Carbide shall only be considered fit for delivery if the proportion of
phosphoretted hydrogen in the crude acetylene does not amount to more
than 0.04 volume per cent. A margin of 0.01 volume per cent. shall be
allowed for the analysis for phosphoretted hydrogen. The whole of the
phosphorus compounds contained in the gas are to be calculated as
phosphoretted hydrogen.

"_Period for Complaints._

"An interval of four weeks from delivery shall be allowed for complaints
for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval
of two weeks for smaller consignments. A complaint shall refer only to a
quantity of carbide remaining at the time of taking the sample.

"_Determination of Quality._

"1. In case the parties do not agree that the consignee is to send to the
analyst for the determination of the quality one unopened and undamaged
drum when the consignment is less than 5000 kilogrammes, and two such
drums when it is over 5000 kilogrammes, a sample for the purpose of
testing the quality is to be taken in the following manner:

"A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is
to be taken. If the delivery to be tested does not comprise more than ten
drums, the sample is to be taken from an unopened and undamaged drum
selected at random. With deliveries of more than ten drums, the sample is
to be drawn from not fewer than 10 per cent, of the lot, and from each of
the unopened and undamaged drums drawn for the purpose not less than 1
kilogramme (= 2.2 lb.) is to be taken.

"The sampling is to be carried out by a trustworthy person appointed by
the two parties, or by one of the experts regularly recognised by the
German Acetylene Association, thus: Each selected drum, before opening,
is to be turned over twice (to got rid of any local accumulation of dust)
and the requisite quantity is to be withdrawn with a shovel (not with the
hand) from any part of it. These samples are immediately shot into one or
more vessels which are closed air- and water-tight. The lid is secured by
a seal. No other description of package, such as cardboard cases, boxes,
&c., is permissible.

"If there is disagreement as to the choice of a trustworthy person, each
of the two parties is to take the required quantity, as specified above.

"2. The yield of gas and the proportion of phosphoretted hydrogen
contained in it are to be determined by the methods prescribed by the
German Acetylene Association. If there are different analyses giving non-
concordant results, an analysis is to be made by the German Acetylene
Association, which shall be accepted as final and binding.

"In cases, however, where the first analysis has been made in the
Laboratory of the German Acetylene Association and arbitration is
required, the decisive analysis shall be made by the Austrian Acetylene
Association. If one of the parties prevents the arbitrator's analysis
being carried out, the analysis of the other party shall be absolutely
binding on him.

"3. The whole of the cost of sampling and analysis is to be borne by the
party in the wrong."

* * * * *

The corresponding regulations issued by the Austrian Acetylene
Association (_Der Oesterreichische Acetylenverein_) are almost
identical with those of the German Association. They contain, however,
provisions that the price is to include packing, that the carbide must
not be delivered in lumps larger than the fist, that the sample may be
sealed in a glass vessel with well-ground glass stopper, that the sample
is to be transmitted to the testing laboratory with particulars of the
size of the lots and the number of drums drawn for sampling, and that the
whole of it is to be gasified in lots of upwards of 1 kilogramme (= 2.2
lb.) apiece.

In Italy, it is enacted by the Board of Agriculture, Commerce and
Industry that by calcium carbide is to be understood for legal purposes
also any other carbide, or carbide-containing mixture, which evolves
acetylene by interaction with water. Also that only calcium carbide,
which on admixture with water yields acetylene containing less than 1 per
cent. of its volume of sulphuretted hydrogen and phosphoretted hydrogen
taken together, may be put on the market.

It is evident from the regulations quoted that the determination of the
volume of gas which a particular sample of calcium carbide is capable of
yielding, when a given weight of it is decomposed under the most
favourable conditions, is a matter of the utmost practical importance to
all interested in the trafficking of carbide, _i.e._, to the makers,
vendors, brokers, and purchasers of that material, as well as to all
makers and users of acetylene generating plant. The regulations of the
British Association do not, however, give details of the method which the
analyst should pursue in determining the yield of acetylene; and while
this may to a certain extent be advantageously left to the discretion of
the competent analyst, it is desirable that the results of the experience
already won by those who have had special opportunities for practising
this branch of analytical work should be embodied in a set of directions
for the analysis of carbide, which may be followed in all ordinary
analyses of that material. By the adoption of such a set of directions as
a provisional standard method, disputes as to the quantity of carbide
will be avoided, while it will still be open to the competent analyst to
modify the method of procedure to meet the requirements of special cases.
It would certainly be unadvisable in the present state of our analytical
methods to accept any hard and fast of rules for analysis for determining
the quality of carbide, but it is nevertheless well to have the best of
existing methods codified for the guidance of analysts. The substance of
the directions issued by the German Association (_Der Deutsche
Acetylenverein_) is reproduced below.


"The greatest precision is attained when the whole of the sample
submitted to the analyst is gasified in a carbide-to-water apparatus, and
the gas evolved is measured in an accurately graduated gasholder.

"The apparatus used for this analysis must not only admit of all the
precautionary rules of gas-analytical work being observed, but must also
fulfil certain other experimental conditions incidental to the nature of
the analysis.

"(_a_) The apparatus must be provided with an accurate thermometer
to show the temperature of the confining water, and with a pressure
gauge, which is in communication with the gasholder.

"(_b_) The generator must either be provided with a gasholder which
is capable of receiving the quantity of gas evolved from the whole amount
of carbide, or the apparatus must be so constructed that it becomes
possible with a gasholder which in not too large (up to 200 litres = say
7 cubic feet capacity) to gasify a larger amount of carbide.

"(_c_) The generator must be constructed so that escape of the
evolved gas from it to the outer air is completely avoided.

"(_d_) The gasholder must be graduated in parts up to 1/4 per cent.
of its capacity, must travel easily, and be kept, as far as may be in
suspension by counterweighting.

"(_e_) The water used for decomposing the carbide and the confining
water must be saturated, before use, with acetylene, and, further, the
generator must, before the analysis proper, be put under the pressure of
the confining (or sealing) liquid."

The following is a description of a typical form of apparatus
corresponding with the foregoing requirements:

"The apparatus, shown in the annexed figure, consists of the generator A,
the washer B, and the gasholder C.


"The generator A consists of a cylindrical vessel with sloping bottom,
provided with a sludge outlet _a_, a gas exit-pipe _b_, and a
lid _b'_ fastened by screws. In the upper part ten boxes _c_
are installed for the purpose of receiving the carbide. The bottoms of
those boxes are flaps which rest through their wire projections on a
revolvable disc _d_, which is mounted on a shaft _l_. This
shaft passes through a stuffing-box to the outside of the generator and
can be rotated by moans of the chains _f_, the pulleys _g_ and
_h_, and the winch _i_. Its rotation causes rotation of the
disc _d_. The disc _d_, on which the bottoms of the carbide-
holders are supported, is provided with a slot _e_. On rotating the
disc, on which the supporting wires of the bottoms of the carbide-holders
rest, the slot is brought beneath these wires in succession; and the


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