Acetylene, The Principles Of Its Generation And Use
by
F. H. Leeds and W. J. Atkinson Butterfield
Part 6 out of 9
employment of a pump. If the gauge shows a fall of pressure of one
quarter of an inch or more in these circumstances, the pipes must be
examined until the leak is located. In the presence of a meter, the
installation can conveniently be tested for soundness by throwing into
it, through the meter, a pressure of 12 inches or so of water from the
weighted holder, then leaving the inlet cock open, and observing whether
the index hand on the lowest dial remains perfectly stationary for a
quarter of an hour--movement of the linger again indicating a leak. The
search for leaks must never be made with a light; if the pipes are full
of air this is useless, if full of gas, criminal in its stupidity. While
the whole installation is still under a pressure of 12 inches thrown from
the loaded holder, whether it contains air or gas, first all the likely
spots (joints, &c.), then the entire length of pipe is carefully brushed
over with strong soapy water, which will produce a conspicuous "soap-
bubble" wherever the smallest flaw occurs. The tightness of a system of
pipes put under pressure from a loaded holder cannot be ascertained
safely by observing the height of the bell, and noting if it falls on
standing. Even if there is no issue of gas from the holder, the position
of the bell will alter with every variation in temperature of the stored
gas or surrounding air, and with every movement of the barometer, rising
as the temperature rises and as the barometer falls, and _vice
versa_, while, unless the water in the seal is saturated with
whatever gas the holder contains, the bell will steadily drop a little an
part of its contents are lost by dissolution in the liquid.
PIPES AND FITTINGS.--As a general rule it is unadvisable to use lead or
composition pipe for permanent acetylene connexions. If exposed, it is
liable to be damaged, and perhaps penetrated by a blow, and if set in the
wall and covered with paper or panel it is liable to be pierced if nails
or tacks should at any time be driven into the wall. There is also an
increased risk in case of fire, owing to its ready fusibility. If used at
all--and it has obvious advantages--lead or composition piping should be
laid on the surface of the walls, &c., and protected from blows, &c., by
a light wooden casing, outwardly resembling the wooden coverings for
electric lighting wires. It has been a common practice, in laying the
underground mains required for supplying the villages which are lighted
by means of acetylene from a central works in different parts of France,
to employ lead pipes. The plan is economical, but in view of the danger
that the main might be flattened by the weight of heavy traction-engines
passing over the roads, or that it might settle into local dips from the
same cause or from the action of subterranean water, in which dips water
would be constantly condensing in cold weather, the use of lead for this
purpose cannot be recommended. Steam-barrel would be preferable to cast
pipe, because permanently sound joints are easier to make in the former,
and because it is not so brittle.
The fittings used for acetylene must have perfectly sound joints and
taps, for the same reasons that the service-pipes must be quite sound.
Common gas-fittings will not do, the joints, taps, ball-sockets, &c., are
not accurately enough ground to prevent leakage. They may in many cases
be improved by regrinding, but often the plug and barrel are so shallow
that it is almost impossible to ensure soundness. It is therefore better
to procure fittings having good taps and joints in the first instance;
the barrels should be long, fairly wide, and there should be no sensible
"play" between plug and barrel when adjusted so that the plug turns
easily when lightly lubricated. Fittings are now being specially made for
acetylene, which is a step in the right direction, because, in addition
to superior taps and joints being essential, smaller bore piping and
smaller through-ways to the taps than are required for coal-gas serve for
acetylene. It is perhaps advisable to add that wherever a rigid bracket
or fitting will answer as well as a jointed one, the latter should on no
account be used; also water-slide pendants should never be employed, as
they are fruitful of accidents, and their apparent advantages are for the
most part illusory. Ball-sockets also should be avoided if possible; if
it is absolutely necessary to have a fitting with a ball-socket, the
latter should have a sleeve made of a short length of sound rubber-tubing
of a size to give a close fit, slipped over so as to join the ball
portion to the socket portion. This sleeve should be inspected once a
quarter at least, and renewed immediately it shows signs of cracking.
Generally speaking all the fittings used should be characterised by
structural simplicity; any ornamental or decorative effects desired may
be secured by proper design without sacrifice of the simplicity which
should always mark the essential and operative parts of the fitting.
Flexible connexions between the fixed service-pipe and a semi-portable or
temporary burner may at times be required. If the connexion is for
permanent use, it must not be of rubber, but of the metallic flexible
tubing which is now commonly employed for such connexions in the case of
coal-gas. There should be a tap between the service-pipe and the flexible
connexion, and this tap should be turned off whenever the burner is out
of use, so that the connexion is not at other times under the pressure
which is maintained in the service-pipes. Unless the connexion is very
short--say 2 feet or less--there should also be a tap at the burner.
These flexible connexions, though serviceable in the case of table-lamps,
&c., of which the position may have to be altered, are undesirable, as
they increase the risk attendant on gas (whether acetylene or other
illuminating gas) lighting, and should, if possible, be avoided. Flexible
connexions may also be required for temporary use, such as for conveying
acetylene to an optical lantern, and if only occasionally called for, the
cost of the metallic flexible tubing will usually preclude its use. It
will generally be found, however, that the whole connexion in such a case
can be of composition or lead gas-piping, connected up at its two ends by
a few inches of flexible rubber tubing. It should be carried along the
walls or over the heads of people who may use the room, rather than
across the floor, or at a low level, and the acetylene should be turned
on to it only when actually required for use, and turned off at the fixed
service-pipe as soon as no longer required. Quite narrow composition
tubing, say 1/4-inch, will carry all the acetylene required for two or
three burners. The cost of a composition temporary connexion will usually
be less than one of even common rubber tubing, and it will be safer. The
composition tubing must not, of course, be sharply bent, but carried by
easy curves to the desired point, and it should be carefully rolled in a
roll of not less than 18 inches diameter when removed. If these
precautions are observed it may be used very many times.
Acetylene service-pipes should, wherever possible, be laid with a fall,
which may be very slight, towards a small closed vessel adjoining the
gasholder or purifier, in order that any water deposited from the gas
owing to condensation of aqueous vapour may run out of the pipe into that
apparatus. Where it is impossible to secure an uninterrupted fall in that
direction, there should be inserted in the service-pipe, at the lowest
point of each dip it makes, a short length of pipe turned downwards and
terminating in a plug or sound tap. Water condensing in this section of
the service-pipe will then run down and collect in this drainage-pipe,
from which it can be withdrawn at intervals by opening the plug or tap
for a moment. The condensed water is thus removed from the service-pipe,
and does not obstruct its through-way. Similar drainage devices may be
used at the lowest points of all dips in mains, though there are special
seal-pots which take the place of the cock or plug used to seal the end
of the drainage-pipe. Such seal-pots or "syphons" are commonly used on
ordinary gas-distributing systems, and might be applied in the case of
large acetylene installations, as they offer facilities for removing the
condensed water from time to time in a convenient and expeditious manner.
EXPULSION OF AIR FROM MAINS.--After a service-pipe system has been proved
to be sound, it is necessary to expel the air from it before acetylene
can be admitted to it with a view to consumption. Unless the system is a
very large one, the expulsion of air is most conveniently effected by
forcing from the gasholder preliminary batches of acetylene through the
pipes, while lights are kept away from the vicinity. This precaution is
necessary because, while the acetylene is displacing the air in the
pipes, they will for some time contain a mixture of air and acetylene in
proportions which fall within the explosive limits of such a mixture. If
the escaping acetylene caught fire from any adjacent light under these
conditions, a most disastrous explosion would ensue and extend through
all the ramifications of the system of pipes. Therefore the first step
when a new system of pipes has to be cleared of air is to see that there
are no lights in or about the house--either fires, lamps, cigars or
pipes, candles or other flames. Obviously this work must be done in the
daytime and finished before nightfall. Burners are removed from two or
more brackets at the farthest points in the system from the gasholder,
and flexible connexions are temporarily attached to them, and led through
a window or door into the open air well clear of the house. One of the
brackets selected should as a rule be the lowest point supplied in the
house. The gasholder having been previously filled with acetylene, the
tap or taps on the pipe leading to the house are turned on, and the
acetylene is passed under slight pressure into the system of pipes, and
escapes through the aforesaid brackets, of which the taps have been
turned on, into the open. The taps of all other brackets are kept closed.
The gas should be allowed to flow thus through the pipes until about five
times the maximum quantity which all the burners on the system would
consume in an hour has escaped from the open brackets. The taps on these
brackets are then closed, and the burners replaced. Flexible tubing is
then connected in place of the burners to all the other brackets in the
house, and acetylene is similarly allowed to escape into the open air
from each for a quarter of an hour. All taps are then closed, and the
burners replaced; all windows in the house are left open wide for half an
hour to allow of the dissipation of any acetylene which may have
accumulated in any part of it, and then, while full pressure from the
gasholder is maintained, a tap is turned on and the gas lighted. If it
burns with a good, fully luminous flame it may be concluded that the
system of pipes is virtually free from air, and the installation may be
used forthwith as required. If, however, the flame is very feebly
luminous, or if the escaping gas does not light, lights must be
extinguished, and the pipes again blown through with acetylene into the
open air. The burner must invariably be in position when a light is
applied, because, in the event of the pipes still containing an explosive
mixture, ignition would not be communicated through the small orifices of
the burner to the mixture in the pipes, and the application of the light
would not entail any danger of an explosion.
Gasfitters familiar with coal-gas should remember, when putting a system
of acetylene pipes into use for the first time, that the range over which
mixtures of acetylene and air are explosive is wider than that over which
mixtures of coal-gas and air are explosive, and that greater care is
therefore necessary in getting the pipes and rooms free from a dangerous
mixture.
The mains for very large installations of acetylene--_e.g._, for
lighting a small town--may advisedly be freed from air by some other plan
than simple expulsion of the air by acetylene, both from the point of
view of economy and of safety. If the chimney gases from a neighbouring
furnace are found on examination to contain not more than about 8 per
cent of oxygen, they may be drawn into the gasholder and forced through
the pipes before acetylene is admitted to them. The high proportion of
carbon dioxide and the low proportion of oxygen in chimney gases makes a
mixture of acetylene and chimney gases non-explosive in any proportions,
and hence if the air is first wholly or to a large extent expelled from a
pipe, main, or apparatus, by means of chimney gases, acetylene may be
admitted, and a much shorter time allowed for the expulsion by it of the
contents of the pipe, before a light is applied at the burners, &c. This
plan, however, will usually only be adopted in the case of very large
pipes, &c.; but on a smaller scale the air may be swept out of a
distributing system by bringing it into connexion with a cylinder of
compressed or liquefied carbon dioxide, the pressure in which will drive
the gas to any spot where an outlet is provided. As these cylinders of
"carbonic acid" are in common employment for preparing aerated waters and
for "lifting" beer, &c., they are easy to hire and use.
TABLE (B).
Giving the Sizes of Pipe which should be used in practice for Acetylene
when the fall of pressure in the Pipe is not to exceed 0.1 inch. (Based
on Morel's formula.)
________________________________________________________
| | |
| Cubic Feet of | Diameters of Pipe to be used up to |
| Acetylene | the lengths indicated. |
| which the Pipe |_______________________________________|
| is required to | | | | | |
| pass in | 1/4 | 3/8 | 1/2 | 3/4 | 1 |
| One Hour. | inch. | inch. | inch. | inch. | inch. |
|________________|_______|_______|_______|_______|_______|
| | | | | | |
| | Feet. | Feet. | Feet. | Feet. | Feet. |
| 1 | 520 | 3960 | 16700 | ... | ... |
| 2 | 130 | 990 | 4170 | ... | ... |
| 3 | 58 | 440 | 1850 | ... | ... |
| 4 | 32 | 240 | 1040 | ... | ... |
| 5 | 21 | 150 | 660 | 5070 | ... |
| 6 | 14 | 110 | 460 | 3520 | ... |
| 7 | 10 | 80 | 340 | 2590 | ... |
| 8 | ... | 62 | 260 | 1980 | ... |
| 9 | ... | 49 | 200 | 1560 | ... |
| 10 | ... | 39 | 160 | 1270 | 5340 |
| 15 | ... | 17 | 74 | 560 | 2370 |
| 20 | ... | 10 | 41 | 310 | 1330 |
| 25 | ... | ... | 26 | 200 | 850 |
| 30 | ... | ... | 18 | 140 | 590 |
| 35 | ... | ... | 13 | 100 | 430 |
| 40 | ... | ... | 10 | 79 | 330 |
| 45 | ... | ... | ... | 62 | 260 |
| 50 | ... | ... | ... | 50 | 210 |
|________________|_______|_______|_______|_______|_______|
TABLE (A).
Showing the Quantities [Q] (in cubic feet) of Acetylene which will pass
in One Hour through Pipes of various diameters (in inches) under
different Falls of Pressure. (Based on Morel's formula.)
____________________________________________________________________
| | | | | | | | | | | | |
| Diameter | | | | | | | | | | | |
| of Pipe | 1/4| 3/8| 1/2| 3/4 | 1 | 1 | 1 | 1 | 2 | 2 | 3 |
| [_d_] = | | | | | | 1/4 | 1/2| 3/4| | 1/2| |
| inches | | | | | | | | | | | |
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.10 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 10 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 25 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 50 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 100 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 200 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 300 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
| 400 | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
| 500 | 1.0| 2.8| 5.8| 15.9| 32.7| 57.1| 90| 132| 185| 320| 510|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.25 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 25 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 50 | 5.1|14.1|28.9| 79.6|163 |285 | 450| 660| 925|1615|2550|
| 100 | 3.6| 9.9|20.4| 56.3|115 |200 | 320| 470| 655|1140|1800|
| 250 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 500 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 1000 | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.50 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 25 |10.2|28.1|57.8|159 |325 |570 | 900|1325|1850|3230|5095|
| 50 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 100 | 5.1|14.1|28.9| 79.6|163 |285 | 450| 660| 925|1615|2550|
| 250 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 500 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 1000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.75 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 50 | 8.8|24.4|50.0|138 |280 |495 | 780|1145|1160|2800|4410|
| 100 | 6.2|17.2|35.4| 97.5|200 |350 | 550| 810|1130|1980|3120|
| 250 | 3.9|10.9|22.4| 61.7|126 |220 | 350| 510| 715|1250|1975|
| 500 | 2.8| 7.7|15.8| 43.6| 89.5|156 | 245| 360| 505| 885|1395|
| 1000 | 2.0| 5.4|11.2| 30.8| 63.3|110 | 174| 255| 360| 625| 985|
| 2000 | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 1.0 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 100 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 250 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 500 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 1000 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 2000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 3000 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
|__________|_________________________________________________________|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 1.5 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 250 | 5.6|15.4|31.6| 87.2|179 |310 | 495| 725|1010|1770|2790|
| 500 | 3.9|10.9|22.4| 61.7|126 |220 | 350| 510| 715|1250|1975|
| 1000 | 2.8| 7.7|15.8| 43.6| 89.5|156 | 245| 360| 505| 885|1395|
| 2000 | 2.0| 5.4|11.2| 30.8| 63.3|110 | 174| 255| 360| 625| 985|
| 3000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 4000 | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 2.0 inches. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 500 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 1000 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 2000 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 3000 | 1.8| 5.1|10.5| 29.1| 59.7|104 | 164| 240| 335| 590| 930|
| 4000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 5000 | 1.4| 4.0| 8.1| 22.5| 46.2| 80.8| 127| 187| 260| 455| 720|
| 6000 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
NOTE.--In order not to impart to the above table the appearance of the
quantities having been calculated to a degree of accuracy which has no
practical significance, quantities of less than 5 cubic feet have been
ignored when the total quantity exceeds 200 cubic feet, and fractions of
a cubic foot have been included only when the total quantity is less than
100 cubic feet.
TABLE (C).
Giving the Sizes of Pipe which should be used in practice for Acetylene
when the fall of pressure in the Pipe is not to exceed 0.25 inch. (Based
on Morel's formula.)
____________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene | Diameters of Pipe to be used up to the lengths stated.|
| which the | |
| Pipe is | |
| required |_______________________________________________________|
| to pass | | | | | | | | |
| in One | 1/4 | 1/2 | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 |
| Hour | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
|____________|______|______|______|______|______|______|______|______|
| | | | | | | | | |
| | Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.|
| 2-1/2 | 1580 | 6680 | 50750| ... | ... | ... | ... | ... |
| 5 | 390 | 1670 | 12690| 53160| ... | ... | ... | ... |
| 7-1/2 | 175 | 710 | 5610| 23760| ... | ... | ... | ... |
| 10 | 99 | 410 | 3170| 13360| 40790| ... | ... | ... |
| 15 | 41 | 185 | 1410| 5940| 18130| 45110| ... | ... |
| 20 | 24 | 105 | 790| 3350| 10190| 25370| 54840| ... |
| 25 | 26 | 67 | 500| 2130| 6520| 16240| 35100| ... |
| 30 | 11 | 46 | 350| 1480| 4530| 11270| 24370| 47520|
| 35 | ... | 34 | 260| 1090| 3330| 8280| 17900| 34910|
| 40 | ... | 26 | 195| 830| 2550| 6340| 13710| 26730|
| 45 | ... | 20 | 155| 660| 2010| 5010| 10830| 21120|
| 50 | ... | 16 | 125| 530| 1630| 4060| 8770| 17110|
| 60 | ... | 11 | 88| 370| 1130| 2880| 6090| 11880|
| 70 | ... | ... | 61| 270| 830| 2070| 4470| 8730|
| 80 | ... | ... | 49| 210| 630| 1580| 3420| 6680|
| 90 | ... | ... | 39| 165| 500| 1250| 2700| 5280|
| 100 | ... | ... | 31| 130| 400| 1010| 2190| 4270|
| 150 | ... | ... | 14| 59| 180| 450| 970| 1900|
| 200 | ... | ... | ... | 33| 100| 250| 540| 1070|
| 250 | ... | ... | ... | 21| 65| 160| 350| 680|
| 500 | ... | ... | ... | ... | 16| 40| 87| 170|
| 1000 | ... | ... | ... | ... | ... | 10| 22| 42|
|____________|______|______|______|______|______|______|______|______|
TABLE (D).
Giving the Sizes of Pipe which should be used in practice for Acetylene
Mains when the fall of pressure in the Main is not to exceed 0.5 inch,
(Based on Morel's formula.)
____________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene | Diameters of Pipe to be used up to the lengths stated.|
| which the | |
| Main is | |
| required |_______________________________________________________|
| to pass | | | | | | | | |
| in One | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 | 2-1/2| 3 |
| Hour | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
|____________|______|______|______|______|______|______|______|______|
| | | | | | | | | |
| |Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|
| 10 | 5.05 | ... | ... | ... | ... | ... | ... | ... |
| 25 | 0.80 | 2.45 | 6.15 | ... | ... | ... | ... | ... |
| 50 | 0.20 | 0.60 | 1.50 | 3.30 | 6.45 | ... | ... | ... |
| 100 | 0.05 | 0.15 | 0.35 | 0.80 | 1.60 | 4.95 |12.30 | ... |
| 200 | ... | 0.04 | 0.09 | 0.20 | 0.40 | 1.20 | 3.05 |12.95 |
| 300 | ... | ... | 0.04 | 0.09 | 0.18 | 0.55 | 1.35 | 5.75 |
| 400 | ... | ... | ... | 0.05 | 0.10 | 0.30 | 0.75 | 3.25 |
| 500 | ... | .. | ... | 0.03 | 0.06 | 0.20 | 0.50 | 2.05 |
| 750 | ... | ... | ... | ... | 0.03 | 0.08 | 0.20 | 0.80 |
| 1100 | ... | ... | ... | ... | ... | 0.05 | 0.12 | 0.50 |
| 1500 | ... | ... | ... | ... | ... | 0.02 | 0.05 | 0.23 |
| 2000 | ... | ... | ... | ... | ... | ... | 0.03 | 0.13 |
| 2500 | ... | ... | ... | ... | ... | ... | 0.02 | 0.08 |
| 5000 | ... | ... | ... | ... | ... | ... | ... | 0.03 |
|____________|______|______|______|______|______|______|______|______|
TABLE (E).
Giving the Sizes of Pipe which should be used in practice for Acetylene
Mains when the fall of pressure in the Main is not to exceed 1.0 inch.
(Based on Morel's formula.)
__________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene |Diameters of Pipe to be used up to the lengths stated|
| which the | |
| Main is | |
| required |_____________________________________________________|
| to pass | | | | | | | | | |
| in One | 3/4 | 1 |1-1/4|1-1/2|1-3/4| 2 |2-1/2| 3 | 4 |
| Hour |inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|
|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
| | | | | | | | | | |
| |Miles|Miles|Miles|Mile.|Miles|Miles|Miles|Miles|Miles|
| 10 | 2.40|10.13|30.90| ... | ... | ... | ... | ... | ... |
| 25 | 0.38| 1.62| 4.94|12.30| ... | ... | ... | ... | ... |
| 50 | 0.09| 0.40| 1.23| 3.07| 6.65|12.96| ... | ... | ... |
| 100 | 0.02| 0.10| 0.30| 0.77| 1.66| 3.24| 9.88| ... | ... |
| 200 | ... | 0.02| 0.07| 0.19| 0.41| 0.81| 2.47| 6.15| ... |
| 300 | ... | 0.01| 0.03| 0.08| 0.18| 0.36| 1.09| 2.73|11.52|
| 400 | ... | ... | 0.0 | 0.05| 0.10| 0.20| 0.61| 1.53| 6.48|
| 500 | ... | ... | 0.0 | 0.03| 0.06| 0.13| 0.39| 0.98| 4.14|
| 750 | ... | ... | ... | 0.01| 0.03| 0.05| 0.17| 0.43| 1.84|
| 1000 | ... | ... | ... | ... | 0.01| 0.03| 0.10| 0.24| 1.03|
| 1500 | ... | ... | ... | ... | ... | 0.01| 0.01| 0.11| 0.46|
| 2000 | ... | ... | ... | ... | ... | ... | 0.02| 0.06| 0.26|
| 2500 | ... | ... | ... | ... | ... | ... | 0.01| 0.04| 0.16|
| 5000 | ... | ... | ... | ... | ... | ... | ... | 0.01| 0.04|
|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
CHAPTER VIII
COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
NATURE OF LUMINOUS FLAMES.--When referring to methods of obtaining
artificial light by means of processes involving combustion or oxidation,
the term "incandescence" is usually limited to those forms of burner in
which some extraneous substance, such as a "mantle," is raised to a
brilliant white heat. Though convenient, the phrase is a mere convention,
for all artificial illuminants, even including the electric light, which
exhibit a useful degree of intensity depend on the same principle of
incandescence. Adopting the convention, however, an incandescent burner
is one in which the fuel burns with a non-luminous or atmospheric flame,
the light being produced by causing that flame to play upon some
extraneous refractory body having the property of emitting much light
when it is raised to a sufficiently high temperature; while a luminous
burner is one in which the fuel is allowed to combine with atmospheric
oxygen in such a way that one or more of the constituents in the gas
evolves light as it suffers combustion. From the strictly chemical point
of view the light-giving substance in the incandescent flame lasts
indefinitely, for it experiences no change except in temperature; whereas
the light-giving substance in a luminous flame lasts but for an instant,
for it only evolves light during the act of its combination with the
oxygen of the atmosphere. Any fluid combustible which burns with a flame
can be made to give light on the incandescent system, for all such
materials either burn naturally, or can be made to burn with a non-
luminous flame, which can be employed to raise the temperature of some
mantle; but only those fuels can be burnt on the self-luminous system
which contain some ingredient that is liberated in the elemental state in
the flame, the said ingredient being one which combines energetically
with oxygen so as to liberate much local heat. In practice, just as there
are only two or three substances which are suitable for the construction
of an incandescent mantle, so there is only one which renders a flame
usefully self-luminous, viz., carbon; and therefore only such fuels as
contain carbon among their constituents can be burnt so as to produce
light without the assistance of the mantle. But inasmuch as it is
necessary for the evolution of light by the combustion of carbon that
that carbon shall be in the free state, only those carbonaceous fuels
yield light without the mantle in which the carbonaceous ingredient is
dissociated into its elements before it is consumed. For instance,
alcohol and carbon monoxide are both combustible, and both contain
carbon; but they yield non-luminous flames, for the carbon burns to
carbon dioxide in ordinary conditions without assuming the solid form;
ether, petroleum, acetylene, and some of the hydrocarbons of coal-gas do
emit light on combustion, for part of their carbon is so liberated. The
quantity of light emitted by the glowing substance increases as the
temperature of that substance rises: the gain in light being equal to the
fifth or higher power of the gain in heat; [Footnote: Calculated from
absolute zero.] therefore unnecessary dissipation of heat from a flame is
one of the most important matters to be guarded against if that flame is
to be an economical illuminant. But the amount of heat liberated when a
certain weight (or volume) of a particular fuel combines with a
sufficient quantity of oxygen to oxidise it wholly is absolutely fixed,
and is exactly the same whether that fuel is made to give a luminous or a
non-luminous flame. Nevertheless the atmospheric flame given by a certain
fuel may be appreciably hotter than its luminous flame, because the
former is usually smaller than the latter. Unless the luminous flame of a
rich fuel is made to expose a wide surface to the air, part of its carbon
may escape ultimate combustion; soot or smoke may be produced, and some
of the most valuable heat-giving substance will be wasted. But if the
flame is made to expose a large surface to the air, it becomes flat or
hollow in shape instead of being cylindrical and solid, and therefore in
proportion to its cubical capacity it presents to the cold air a larger
superficies, from which loss of heat by radiation, &c., occurs. Being
larger, too, the heat produced is less concentrated.
It does not fall within the province of the present book to discuss the
relative merits of luminous and incandescent lighting; but it may be
remarked that acetylene ranks with petroleum against coal-gas,
carburetted or non-carburetted water-gas, and semi-water-gas, in showing
a comparatively small degree of increased efficiency when burnt under the
mantle. Any gas which is essentially composed of carbon monoxide or
hydrogen alone (or both together) burns with a non-luminous flame, and
can therefore only be used for illuminating purposes on the incandescent
system; but, broadly speaking, the higher is the latent illuminating
power of the gas itself when burnt in a non-atmospheric burner, the less
marked is the superiority, both from the economical and the hygienic
aspect, of its incandescent flame. It must be remembered also that only a
gas yields a flame when it is burnt; the flame of a paraffin lamp and of
a candle is due to the combustion of the vaporised fuel. Methods of
burning acetylene under the mantle are discussed in Chapter IX.; here
only self-luminous flames are being considered, but the theoretical
question of heat economy applies to both processes.
Heat may be lost from a flame in three several ways: by direct radiation
and conduction into the surrounding air, among the products of
combustion, and by conduction into the body of the burner. Loss of heat
by radiation and conduction to the air will be the greater as the flame
exposes a larger surface, and as a more rapid current of cold air is
brought into proximity with the flame. Loss of heat by conduction, into
the burner will be the greater as the material of which the burner is
constructed is a better conductor of heat, and as the mass of material in
that burner is larger. Loss of heat by passage into the combustion
products will also be greater as these products are more voluminous; but
the volume of true combustion products from any particular gas is a fixed
quantity, and since these products must leave the flame at the
temperature of that flame--where the highest temperature possible is
requisite--it would seem that no control can be had over the quantity of
heat so lost. However, although it is not possible in practice to supply
a flame with too little air, lest some of its carbon should escape
consumption and prove a nuisance, it is very easy without conspicuous
inconvenience to supply it with too much; and if the flame is supplied
with too much, there is an unnecessary volume of air passing through it
to dilute the true combustion products, which air absorbs its own proper
proportion of heat. It is only the oxygen of the air which a flame needs,
and this oxygen is mixed with approximately four times its volume of
nitrogen; if, then, only a small excess of oxygen (too little to be
noticeable of itself) is admitted to a flame, it is yet harmful, because
it brings with it four times its volume of nitrogen, which has to be
raised to the same temperature as the oxygen. Moreover, the nitrogen and
the excess of oxygen occupy much space in the flame, making it larger,
and distributing that fixed quantity of heat which it is capable of
generating over an unnecessarily large area. It is for this reason that
any gas gives so much brighter a light when burnt in pure oxygen than in
air, (1) because the flame is smaller and its heat more concentrated, and
(2) because part of its heat is not being wasted in raising the
temperature of a large mass of inert nitrogen. Thus, if the flame of a
gas which naturally gives a luminous flame is supplied with an excess of
air, its illuminating value diminishes; and this is true whether that
excess is introduced at the base of the actual flame, or is added to the
gas prior to ignition. In fact the method of adding some air to a
naturally luminous gas before it arrives at its place of combustion is
the principle of the Bunsen burner, used for incandescent lighting and
for most forms of warming and cooking stoves. A well-made modern
atmospheric burner, however, does not add an excess of air to the flame,
as might appear from what has been said; such a burner only adds part of
the air before and the remainder of the necessary quantity after the
point of first ignition--the function of the primary supply being merely
to insure thorough admixture and to avoid the production of elemental
carbon within the flame.
ILLUMINATING POWER.--It is very necessary to observe that, as the
combined losses of heat from a flame must be smaller in proportion to the
total heat produced by the flame as the flame itself becomes larger, the
more powerful and intense any single unit of artificial light is, the
more economical does it become, because economy of heat spells economy of
light. Conversely, the more powerful and intense any single unit of light
is, the more is it liable to injure the eyesight, the deeper and, by
contrast, the more impenetrable are the shadows it yields, and the less
pleasant and artistic is its effect in an occupied room. For economical
reasons, therefore, one large central source of light is best in an
apartment, but for physiological and aesthetic reasons a considerable
number of correspondingly smaller units are preferable. Even in the
street the economical advantage of the single unit is outweighed by the
inconvenience of its shadows, and by the superiority of a number of
evenly distributed small sources to one central large source of light
whenever the natural transmission of light rays through the atmosphere is
interfered with by mist or fog. The illuminating power of acetylene is
commonly stated to be "240 candles" (though on the same basis Wolff has
found it to be about 280 candles). This statement means that when
acetylene is consumed in the most advantageous self-luminous burner at
the most advantageous rate, that rate (expressed in cubic feet per hour)
is to 5 in the same ratio as the intensity of the light evolved
(expressed in standard candles) is to the said "illuminating power."
Thus, Wolff found that when acetylene was burnt in the "0000 Bray" fish-
tail burner at the rate of 1.377 cubic feet per hour, a light of 77
candle-power was obtained. Hence, putting x to represent the illuminating
power of the acetylene in standard candles, we have:
1.377 / 5 = 77 / x hence x = 280.
Therefore acetylene is said to have, according to Wolff, an illuminating
power of about 280 candles, or according to other observers, whose
results have been commonly quoted, of 240 candles. The same method of
calculating the nominal illuminating power of a gas is applied within the
United Kingdom in the case of all gases which cannot be advantageously
burnt at the rate of 5 cubic feet per hour in the standard burner
(usually an Argand). The rate of 5 cubic feet per hour is specified in
most Acts of Parliament relating to gas-supply as that at which coal-gas
is to be burnt in testings of its illuminating power; and the
illuminating power of the gas is defined as the intensity, expressed in
standard candles, of the light afforded when the gas is burnt at that
rate. In order to make the values found for the light evolved at more
advantageous rates of consumption by other descriptions of gas--such as
oil-gas or acetylene--comparable with the "illuminating power" of coal-
gas as defined above, the values found are corrected in the ratio of the
actual rate of consumption to 5 cubic feet per hour.
In this way the illuminating power of 240 candles has been commonly
assigned to acetylene, though it would be clearer to those unfamiliar
with the definition of illuminating power in the Acts of Parliament which
regulate the testing of coal-gas, if the same fact were conveyed by
stating that acetylene affords a maximum illuminating power of 48 candles
(_i.e._, 240 / 5) per cubic foot. Actually, by misunderstanding of
the accepted though arbitrary nomenclature of gas photometry, it has not
infrequently been assorted or implied that a cubic foot of acetylene
yields a light of 240 candle-power instead of 48 candle-power. It should,
moreover, be remembered that the ideal illuminating power of a gas is the
highest realisable in any Argand or flat-flame burner, while the said
burner may not be a practicable one for general use in house lighting.
Thus, the burners recommended for general use in lighting by acetylene do
not develop a light of 48 candles per cubic foot of gas consumed, but
considerably less, as will appear from the data given later in this
chapter.
It has been stated that in order to avoid loss of heat from a flame
through the burner, that burner should present only a small mass of
material (_i.e._, be as light in weight as possible), and should be
constructed of a bad heat-conductor. But if a small mass of a material
very deficient in heat-conducting properties comes in contact with a
flame, its temperature rises seriously and may approach that of the base
of the flame itself. In the case of coal-gas this phenomenon is not
objectionable, is even advantageous, and it explains why a burner made of
steatite, which conducts heat badly, in always more economical (of heat
and therefore of light) than an iron one. In the case of acetylene the
same rule should, and undoubtedly does, apply also; but it is
complicated, and its effect sometimes neutralised, by a peculiarity of
the gas itself. It has been shown in Chapters II. and VI. that acetylene
polymerises under the influence of heat, being converted into other
bodies of lower illuminating power, together with some elemental carbon.
If, now, acetylene is fed into a burner which, being composed of some
material like steatite possessed of low heat-conducting and radiating
powers, is very hot, and if the burner comprises a tube of sensible
length, the gas that actually arrives at the orifice may no longer be
pure acetylene, but acetylene diluted with inferior illuminating agents,
and accompanied by a certain proportion of carbon. Neglecting the effect
of this carbon, which will be considered in the following paragraph, it
is manifest that the acetylene issuing from a hot burner--assuming its
temperature to exceed the minimum capable of determining polymerisation--
may emit less light per unit of volume than the acetylene escaping from a
cold burner. Proof of this statement is to be found in some experiments
described by Bullier, who observed that when a small "Manchester" or
fish-tail burner was allowed to become naturally hot, the quantity of gas
needed to give the light of one candle (uncorrected) was 1.32 litres, but
when the burner was kept cool by providing it with a jacket in which
water was constantly circulating, only 1.13 litres of acetylene were
necessary to obtain the same illuminating value, this being an economy of
16 per cent.
EARLY BURNERS.--One of the chief difficulties encountered in the early
days of the acetylene industry was the design of a satisfactory burner
which should possess a life of reasonable length. The first burners tried
were ordinary oil-gas jets, which resemble the fish-tails used with coal-
gas, but made smaller in every part to allow for the higher illuminating
power of the oil-gas or acetylene per unit of volume. Although the flames
they gave were very brilliant, and indeed have never been surpassed, the
light quickly fell off in intensity owing to the distortion of their
orifices caused by the deposition of solid matter at the edges. Various
explanations have been offered to account for the precipitation of solid
matter at the jets. If the acetylene passes directly to the burner from a
generator having carbide in excess without being washed or filtered in
any way, the gas may carry with it particles of lime dust, which will
collect in the pipes mainly at the points where they are constricted; and
as the pipes will be of comparatively large bore until the actual burner
is readied, it will be chiefly at the orifices where the deposition
occurs. This cause, though trivial, is often overlooked. It will be
obviated whenever the plant is intelligently designed. As the phosphoric
anhydride, or pentoxide, which is produced when a gas containing
phosphorus burns, is a solid body, it may be deposited at the burner
jets. This cause may be removed, or at least minimised, by proper
purification of the acetylene, which means the removal of phosphorus
compounds. Should the gas contain hydrogen silicide siliciuretted
hydrogen), solid silica will be produced similarly, and will play its
part in causing obstruction. According to Lewes the main factor in the
blocking of the burners is the presence of liquid polymerised products in
the acetylene, benzene in particular; for he considers that these bodies
will be absorbed by the porous steatite, and will be decomposed under the
influence of heat in that substance, saturating the steatite with carbon
which, by a "catalytic" action presumably, assists in the deposition of
further quantities of carbon in the burner tube until distortion of the
flame results. Some action of this character possibly occurs; but were it
the sole cause of blockage, the trouble would disappear entirely if the
gas were washed with some suitable heavy oil before entering the burners,
or if the latter were constructed of a non-porous material. It is
certainly true that the purer is the acetylene burnt, both as regards
freedom from phosphorus and absence of products of polymerisation, the
longer do the burners last; and it has been claimed that a burner
constructed at its jets of some non-porous substance, e.g., "ruby," does
not choke as quickly as do steatite ones. Nevertheless, stoppages at the
burners cannot be wholly avoided by these refinements. Gaud has shown
that when pure acetylene is burnt at the normal rate in 1-foot Bray jets,
growths of carbon soon appear, but do not obstruct the orifices during
100 hours' use; if, however, the gas-supply is checked till the flame
becomes thick, the growths appear more quickly, and become obstructive
after some 60 hours' burning. On the assumption that acetylene begins to
polymerise at a temperature of 100 deg. C., Gaud calculates that
polymerisation cannot cause blocking of the burners unless the speed of
the passing gas is so far reduced that the burner is only delivering one-
sixth of its proper volume. But during 1902 Javal demonstrated that on
heating in a gas-flame one arm of a twin, non-injector burner which had
been and still was behaving quite satisfactorily with highly purified
acetylene, growths were formed at the jet of that arm almost
instantaneously. There is thus little doubt that the principal cause of
this phenomenon is the partial dissociation of the acetylene (i.e.,
decomposition into its elements) as it passes through the burner itself;
and the extent of such dissociation will depend, not at all upon the
purity of the gas, but upon the temperature of the burner, upon the
readiness with which the heat of the burner is communicated to the gas,
and upon the speed at which the acetylene travels through the burner.
Some experiments reported by R. Granjon and P. Mauricheau-Beaupre in 1906
indicate, however, that phosphine in the gas is the primary cause of the
growths upon non-injector burners. According to these investigators the
combustion of the phosphine causes a deposit at the burner orifices of
phosphoric acid, which is raised by the flame to a temperature higher
than that of the burner. This hot deposit then decomposes some acetylene,
and the carbon deposited therefrom is rendered incombustible by the
phosphoric acid which continues to be produced from the combustion of the
phosphine in the gas. The incombustible deposit of carbon and phosphoric
acid thus produced ultimately chokes the burner.
It will appear in Chapter XI. that some of the first endeavours to avoid
burner troubles were based on the dilution of the acetylene with carbon
dioxide or air before the gas reached the place of combustion; while the
subsequent paragraphs will show that the same result is arrived at more
satisfactorily by diluting the acetylene with air during its actual
passage through the burner. It seems highly probable that the beneficial
effect of the earliest methods was due simply or primarily to the
dilution, the molecules of the acetylene being partially protected from
the heat of the burner by the molecules of a gas which was not injured by
the high temperature, and which attracted to itself part of the heat that
would otherwise have been communicated to the hydrocarbon. The modern
injector burner exhibits the same phenomenon of dilution, and is to the
same extent efficacious in preventing polymerisation; but inasmuch as it
permits a larger proportion of air to be introduced, and as the addition
is made roughly half-way along the burner passage, the cold air is more
effectual in keeping the former part of the tip cool, and in jacketing
the acetylene during its travel through the latter part, the bore of
which is larger than it otherwise would be.
INJECTOR AND TWIN-FLAME BURNERS.--In practice it is neither possible to
cool an acetylene burner systematically, nor is it desirable to construct
it of such a large mass of some good heat conductor that its temperature
always remains below the dissociation point of the gas. The earliest
direct attempts to keep the burner cool were directed to an avoidance of
contact between the flame of the burning acetylene and the body of the
jet, this being effected by causing the current of acetylene to inject a
small proportion of air through lateral apertures in the burner below the
point of ignition. Such air naturally carries along with it some of the
heat which, in spite of all precautions, still reaches the burner; but it
also apparently forms a temporary annular jacket round the stream of gas,
preventing it from catching fire until it has arrived at an appreciable
distance from the jet. Other attempts were made by placing two non-
injector jets in such mutual positions that the two streams of gas met at
an angle, there to spread fan-fashion into a flat flame. This is really
nothing but the old fish-tail coal-gas burner--which yields its flat
flame by identical impingement of two gas streams--modified in detail so
that the bulk of the flame should be at a considerable distance from the
burner instead of resting directly upon it. In the fish-tail the two
orifices are bored in the one piece of steatite, and virtually join at
their external ends; in the acetylene burner, two separate pieces of
steatite, three-quarters of an inch or more apart, carried by completely
separate supports, are each drilled with one hole, and the flame stands
vertically midway between them. The two streams of gas are in one
vertical plane, to which the vertical plane of the flame is at right
angles. Neither of these devices singly gave a solution of the
difficulty; but by combining the two--the injector and the twin-flame
principle--the modern flat-flame acetylene burner has been evolved, and
is now met with in two slightly different forms known as the Billwiller
and the Naphey respectively. The latter apparently ought to be called the
Dolan.
[Illustration: FIG. 8.--TYPICAL ACETYLENE BURNERS.]
The essential feature of the Naphey burner is the tip, which is shown in
longitudinal section at A in Fig. 8. It consists of a mushroom headed
cylinder of steatite, drilled centrally with a gas passage, which at its
point is of a diameter suited to pass half the quantity of acetylene that
the entire burner is intended to consume. The cap is provided with four
radial air passages, only two of which are represented in the drawing;
these unite in the centre of the head, where they enter into the
longitudinal channel, virtually a continuation of the gas-way, leading to
the point of combustion by a tube wide enough to pass the introduced air
as well as the gas. Being under some pressure, the acetylene issuing from
the jet at the end of the cylindrical portion of the tip injects air
through the four air passages, and the mixture is finally burnt at the
top orifice. As pointed out in Chapter VII., the injector jet is so small
in diameter that even if the service-pipes leading to the tip contain an
explosive mixture of acetylene and air, the explosion produced locally if
a light is applied to the burner cannot pass backwards through that jet,
and all danger is obviated. One tip only of this description evidently
produces a long, jet-like flame, or a "rat-tail," in which the latent
illuminating power of the acetylene is not developed economically. In
practice, therefore, two of these tips are employed in unison, one of the
commonest methods of holding them being shown at B. From each tip issues
a stream of acetylene mixed with air, and to some extent also surrounded
by a jacket of air; and at a certain point, which forms the apex of an
isosceles right-angled triangle having its other angles at the orifices
of the tips, the gas streams impinge, yielding a flat flame, at right-
angles, as mentioned before, to the plane of the triangle. If the two
tips are three-quarters of an inch apart, and if the angle of impingement
is exactly 90 deg., the distance of each tip from the base of the flame
proper will be a trifle over half an inch; and although each stream of
gas does take fire and burn somewhat before meeting its neighbour,
comparatively little heat is generated near the body of the steatite.
Nevertheless, sufficient heat is occasionally communicated to the metal
stems of these burners to cause warping, followed by a want of alignment
in the gas streams, and this produces distortion of the flame, and
possibly smoking. Three methods of overcoming this defect have been used:
in one the arms are constructed entirely of steatite, in another they are
made of such soft metal as easily to be bent back again into position
with the fingers or pliers, in the third each arm is in two portions,
screwing the one into the other. The second type is represented by the
original Phos burner, in which the curved arms of B are replaced by a
pair of straight divergent arms of thin, soft tubing, joined to a pair of
convergent wider tubes carrying the two tips. The third type is met with
in the Drake burner, where the divergent arms are wide and have an
internal thread into which screws an external thread cut upon lateral
prolongations of the convergent tubes. Thus both the Phos and the Drake
burner exhibit a pair of exposed elbows between the gas inlet and the two
tips; and these elbows are utilised to carry a screwed wire fastened to
an external milled head by means of which any deposit of carbon in the
burner tubes can be pushed out. The present pattern of the Phos burner is
shown in Fig. 9, in which _A_ is the burner tip, _B_ the wire
or needle, and _C_ the milled head by which the wire is screwed in
and out of the burner tube.
[Illustration: FIG. 9.--IMPROVED PHOS BURNER.]
[Illustration: FIG. 10.--"WONDER" SINGLE AND TWO-FLAME BURNERS.]
[Illustration: FIG. 11.--"SUPREMA" NO. 266651, TWO-FLAME BURNER.]
[Illustration: FIG. 12.--BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP.]
[Illustration: FIG. 13.--BRAY'S "ELTA" BURNER.]
[Illustration: FIG. 14.--BRAY'S "LUTA" BURNER.]
[Illustration: FIG. 15.--BRAY'S "SANSAIR" BURNER.]
[Illustration: FIG. 16.--ADJUSTABLE "KONA" BURNER.]
In the original Billwiller burner, the injector gas orifice was brought
centrally under a somewhat larger hole drilled in a separate sheet of
platinum, the metal being so carried as to permit entry of air. In order
to avoid the expense of the platinum, the same principle was afterwards
used in the design of an all-steatite head, which is represented at D in
Fig. 8. The two holes there visible are the orifices for the emission of
the mixture of acetylene with indrawn air, the proper acetylene jets
lying concentrically below these in the thicker portions of the heads.
These two types of burner have been modified in a large number of ways,
some of which are shown at C, E, and F; the air entering through saw-
cuts, lateral holes, or an annular channel. Burners resembling F in
outward form are made with a pair of injector jets and corresponding air
orifices on each head, so as to produce a pair of names lying in the same
plane, "end-on" to one another, and projecting at either side
considerably beyond the body of the burner; these have the advantage of
yielding no shadow directly underneath. A burner of this pattern, viz.,
the "Wonder," which is sold in this country by Hannam's, Ltd., is shown
in Fig. 10, alongside the single-flame "Wonder" burner, which is largely
used, especially in the United States. Another two-flame burner, made of
steatite, by J. von Schwarz of Nuremberg, and sold by L. Wiener of
London, is shown in Fig. 11. Burners of the Argand type have also been
manufactured, but have been unsuccessful. There are, of course, endless
modifications of flat-flame burners to be found on the markets, but only
a few need be described. A device, which should prove useful where it may
be convenient to be able to turn one or more burners up or down from the
same common distant spot, has been patented by Forbes. It consists of the
usual twin-injector burner fitted with a small central pinhole jet; and
inside the casing is a receptacle containing a little mercury, the level
of which is moved by the gas pressure by an adaptation of the
displacement principle. When the main is carrying full pressure, both of
the jets proper are alight, and the burner behaves normally, but if the
pressure is reduced to a certain point, the movement of the mercury seals
the tubes leading to the main jets, and opens that of the pilot flame,
which alone remains alight till the pressure is increased again. Bray has
patented a modification of the Naphey injector tip, which is shown in
Fig. 12. It will be observed that the four air inlets are at right-angles
to the gas-way; but the essential feature of the device is the conical
orifice. By this arrangement it is claimed that firing back never occurs,
and that the burner can be turned down and left to give a small flame for
considerable periods of time without fear of the apertures becoming
choked or distorted. As a rule burners of the ordinary type do not well
bear being turned down; they should either be run at full power or
extinguished completely. The "Elta" burner, made by Geo. Bray and Co.,
Ltd., which is shown in Fig. 13, is an injector or atmospheric burner
which may be turned low without any deposition of carbon occurring on the
tips. A burner of simple construction but which cannot be turned low is
the "Luta," made by the same firm and shown in Fig. 14. Of the non-
atmospheric type the "Sansair," also made by Geo. Bray and Co., Ltd., is
extensively used. It is shown in Fig. 15. In order to avoid the warping,
through the heat of the flame, of the arms of burners which sometimes
occurs when they are made of metal, a number of burners are now made with
the arms wholly of steatite. One of the best-known of these, of the
injector type, is the "Kona," made by Falk, Stadelmann and Co., of
London. It is shown in Fig. 16, fitted with a screw device for adjusting
the flow of gas, so that when this adjuster has been set to give a flame
of the proper size, no further adjustment by means of the gas-tap is
necessary. This saves the trouble of manipulating the tap after the gas
is lighted. The same adjusting device may also be had fitted to the Phos
burner (Fig. 9) or to the "Orka" burner (Fig. 17), which is a steatite-
tip injector burner with metal arms made by Falk, Stadelmann and Co.,
Ltd. A burner with steatite arms, made by J. von Schwarz of Nuremberg,
and sold in this country by L. Wiener of London, is shown in Fig. 18.
[Illustration: FIG. 17.--"ORKA" BURNER.]
[Illustration: FIG. 18.--"SUPREMA" NO. 216469 BURNER.]
ILLUMINATING DUTY.--The illuminating value of ordinary self-luminous
acetylene burners in different sizes has been examined by various
photometrists. For burners of the Naphey type Lewes gives the following
table:
___________________________________________________________
| | | | | |
| | | Gas | | Candles |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|_________|___________|____________|__________|_____________|
| | | | | |
| No. 6 | 2.0 | 0.155 | 0.794 | 5.3 |
| " 8 | 2.0 | 0.27 | 3.2 | 11.6 |
| " 15 | 2.0 | 0.40 | 8.0 | 20.0 |
| " 25 | 2.0 | 0.65 | 17.0 | 26.6 |
| " 30 | 2.0 | 0.70 | 23.0 | 32.85 |
| " 42 | 2.0 | 1.00 | 34.0 | 34.0 |
|_________|___________|____________|__________|_____________|
From burners of the Billwiller type Lewes obtained in 1899 the values:
___________________________________________________________
| | | | | |
| | | Gas | | Candles |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|_________|___________|____________|__________|_____________|
| | | | | |
| No. 1 | 2.0 | 0.5 | 7.0 | 11.0 |
| " 2 | 2.0 | 0.75 | 21.0 | 32.0 |
| " 3 | 2.0 | 0.75 | 28.0 | 37.3 |
| " 4 | 3.0 | 1.2 | 48.0 | 40.0 |
| " 5 | 3.5 | 2.0 | 76.0 | 38.0 |
|_________|___________|____________|__________|_____________|
Neuberg gives these figures for different burners (1900) as supplied by
Pintsch:
______________________________________________________________________
| | | | | |
| | Gas | | Candles | |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|____________________|___________|____________|__________|_____________|
| | | | | |
| No. 0, slit burner | 3.9 | 1.59 | 59.2 | 37.3 |
| " 00000 fishtail | 1.6 | 0.81 | 31.2 | 38.5 |
| Twin burner No. 1 | 3.2 | 0.32 | 13.1 | 40.8 |
| " " " 2 | 3.2 | 0.53 | 21.9 | 41.3 |
| " " " 3 | 3.2 | 0.74 | 31.0 | 41.9 |
| " " " 4 | 3.2 | 0.95 | 39.8 | 41.9 |
|____________________|___________|____________|__________|_____________|
The actual candle-power developed by each burner was not quoted by
Neuberg, and has accordingly been calculated from his efficiency values.
It is noteworthy, and in opposition to what has been found by other
investigators as well as to strict theory, that Neuberg represents the
efficiencies to be almost identical in all sizes of the same description
of burner, irrespective of the rate at which it consumes gas.
Writing in 1902, Capelle gave for Stadelmann's twin injector burners the
following figures; but as he examined each burner at several different
pressures, the values recorded in the second, third, and fourth columns
are maxima, showing the highest candle-power which could be procured from
each burner when the pressure was adjusted so as to cause consumption to
proceed at the most economical rate. The efficiency values in the fifth
column, however, are the mean values calculated so as to include all the
data referring to each burner. Capelle's results have been reproduced
from the original on the basis that 1 _bougie decimale_ equals 0.98
standard English candle, which is the value he himself ascribes to it (1
_bougie decimale_ equals 1.02 candles is the value now accepted).
_____________________________________________________________________
| | | | | |
| Nominal | Best | Actual Consumption | Maximum | Average |
| Consumption,| Pressure| at Stated Pressure. | Light in | Candles per|
| Litres. | Inches. | Cubic Feet per Hour.| Candles. | Cubic Foot.|
|_____________|_________|_____________________|__________|____________|
| | | | | |
| 10 | 3.5 | 0.40 | 8.4 | 21.1 |
| 15 | 2.8 | 0.46 | 16.6 | 33.3 |
| 20 | 3.9 | 0.64 | 25.1 | 40.0 |
| 25 | 3.5 | 0.84 | 37.8 | 46.1 |
| 30 | 3.5 | 0.97 | 48.2 | 49.4 |
|_____________|_________|_____________________|__________|____________|
Some testings of various self-luminous burners of which the results were
reported by R. Granjon in 1907, gave the following results for the duty
of each burner, when the pressure was regulated for each burner to that
which afforded the maximum illuminating duty. The duty in the original
paper is given in litres per Carcel-hour. The candle has been taken as
equal to 0.102 Carcel for the conversion to candles per cubic foot.
___________________________________________________________________
| | | | |
| | Nominal | Best | Duty. Candles |
| Burner. | Consumption.| Pressure. | per cubic foot. |
|_______________________|_____________|__________ |_________________|
| | | | |
| | Litres. | Inches. | |
| Twin . . . . | 10 | 2.76 | 21.2 |
| " . . . . | 20 | 2.76 | 23.5 |
| " . . . . | 25 | 3.94 | 30.2 |
| " . . . . | 30 | 3.94-4.33 | 44.8 |
| ", (pair of flames) | 35 | 3.55-3.94 | 45.6 |
| Bray's "Manchester" | 6 | 1.97 | 18.8 |
| " | 20 | 1.97 | 35.6 |
| " | 40 | 2.36 | 42.1 |
| Rat-tail . . . | 5 | 5.5 | 21.9 |
| " . . . | 8 | 4.73 | 25.0 |
| Slit or batswing . | 30 | 1.97-2.36 | 37.0 |
|_______________________|_____________|___________|_________________|
Granjon has concluded from his investigations that the Manchester or
fish-tail burners are economical when they consume 0.7 cubic foot per
hour and when the pressure is between 2 and 2.4 inches. When these
burners are used at the pressure most suitable for twin burners their
consumption is about one-third greater than that of the latter per
candle-hour. The 25 to 35 litres-per-hour twin burners should be used at
a pressure higher by about 1 inch than the 10 to 20 litres-per-hour twin
burners.
At the present time, when the average burner has a smaller hourly
consumption than 1 foot per hour, it is customary in Germany to quote the
mean illuminating value of acetylene in self-luminous burners as being 1
Hefner unit per 0.70 litre, which, taking
1 Hefner unit = 0.913 English candle
1 English candle = 1.095 Hefner units,
works out to an efficiency of 37 candles per foot in burners probably
consuming between 0.5 and 0.7 foot per hour.
Even when allowance is made for the difficulties in determining
illuminating power, especially when different photometers, different
standards of light, and different observers are concerned, it will be
seen that these results are too irregular to be altogether trustworthy,
and that much more work must be done on this subject before the economy
of the acetylene flame can be appraised with exactitude. However, as
certain fixed data are necessary, the authors have studied those and
other determinations, rejecting some extreme figures, and averaging the
remainder; whence it appears that on an average twin-injector burners of
different sizes should yield light somewhat as follows:
_______________________________________________________
| | | |
| Size of Burner in | Candle-power | Candles |
| Cubic Feet per Hour. | Developed. | per Cubic Foot. |
|______________________|______________|_________________|
| | | |
| 0.5 | 18.0 | 35.9 |
| 0.7 | 27.0 | 38.5 |
| 1.0 | 45.6 | 45.6 |
|______________________|______________|_________________|
In the tabular statement in Chapter I. the 0.7-foot burner was taken as
the standard, because, considering all things, it seems the best, to
adopt for domestic purposes. The 1-foot burner is more economical when in
the best condition, but requires a higher gas pressure, and is rather too
powerful a unit light for good illuminating effect; the 0.5 burner
naturally gives a better illuminating effect, but its economy is
surpassed by the 0.7-foot burner, which is not too powerful for the human
eye.
For convenience of comparison, the illuminating powers and duties of the
0.5- and 0.7-foot acetylene burners may be given in different ways:
ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE.
_0.7-foot Burner._ | _Half-foot Burner._
|
1 litre = 1.36 candles. | 1 litre = 1.27 candles.
1 cubic foot = 38.5 candles. | 1 cubic foot = 35.9 candles.
1 candle = 0.736 litre. | 1 candle = 0.79 litre.
1 candle = 0.026 cubic foot. | 1 candle = 0.028 cubic foot.
If the two streams of gas impinge at an angle of 90 deg., twin-injector
burners for acetylene appear to work best when the gas enters them at a
pressure of 2 to 2.5 inches; for a higher pressure the angle should be
made a little acute. Large burners require to have a wider distance
between the jets, to be supplied with acetylene at a higher pressure, and
to be constructed with a smaller angle of impingement. Every burner, of
whatever construction and size, must always be supplied with gas at its
proper pressure; a pressure varying from time to time is fatal.
It is worth observing that although injector burners are satisfactory in
practice, and are in fact almost the only jets yet found to give
prolonged satisfaction, the method of injecting air below the point of
combustion in a self-luminous burner is in some respects wrong in
principle. If acetylene can be consumed without polymerisation in burners
of the simple fish-tail or bat's-wing type, it should show a higher
illuminating efficiency. In 1902 Javal stated that it was possible to
burn thoroughly purified acetylene in twin non-injector burners, provided
the two jets, made of steatite as usual, were arranged horizontally
instead of obliquely, the two streams of gas then meeting at an angle of
180 deg., so as to yield an almost circular flame. According to Javal,
whereas carbonaceous growths were always produced in non-injector
acetylene burners with either oblique or horizontal jets, in the former
case the growths eventually distorted the gas orifices, but in the latter
the carbon was deposited in the form of a tube, and fell off from the
burner by its own weight directly it had grown to a length of 1.2 or 1.5
millimetres, leaving the jets perfectly clear and smooth. Javal has had
such a burner running for 10 or 12 hours per day for a total of 2071
hours; it did not need cleaning out on any occasion, and its consumption
at the end of the period was the same as at first. He found that it was
necessary that the tips should be of steatite, and not of metal or glass;
that the orifices should be drilled in a flat surface rather than at the
apex of a cone, and that the acetylene should be purified to the utmost
possible extent. Subsequent experience has demonstrated the possibility
of constructing non-injector burners such as that shown in Fig. 13, which
behave satisfactorily even though the jets are oblique. But with such
burners trouble will inevitably ensue unless the gas is always purified
to a high degree and is tolerably dry and well filtered. Non-injector
burners should not be used unless special care is taken to insure that
the installation is consistently operated in an efficient manner in these
respects.
GLOBES, &C.--It does not fall within the province of the present volume
to treat at length of chimneys, globes, or the various glassware which
may be placed round a source of light to modify its appearance. It should
be remarked, however, that obedience to two rules is necessary for
complete satisfaction in all forms of artificial illumination. First, no
light much stronger in intensity than a single candle ought ever to be
placed in such a position in an occupied room that its direct rays can
reach the eye, or the vision will be temporarily, and may be permanently,
injured. Secondly, unless economy is to be wholly ignored, no coloured or
tinted globe or shade should ever be put round a source of artificial
light. The best material for the construction of globes is that which
possesses the maximum of translucency coupled with non-transparency,
_i.e._, a material which passes the highest proportion of the light
falling upon it, and yet disperses that light in such different
directions that the glowing body cannot be seen through the globe. Very
roughly speaking, plain white glass, such as that of which the chimneys
of oil-lamps and incandescent gas-burners are composed, is quite
transparent, and therefore affords no protection to the eyesight; a
protective globe should be rather of ground or opal glass, or of plain
glass to which a dispersive effect has been given by forming small prisms
on its inner or outer surface, or both. Such opal, ground, or dispersive
shades waste much light in terms of illuminating power, but waste
comparatively little in illuminating effect well designed, they may
actually increase the illuminating effect in certain positions; a tinted
globe, even if quite plain in figure, wastes both illuminating power and
effect, and is only to be tolerated for so-believed aesthetic reasons.
Naturally no globe must be of such figure, or so narrow at either
orifice, as to distort the shape of the unshaded acetylene flame--it is
hardly necessary to say this now, but some years ago coal-gas globes were
constructed with an apparent total disregard of this fundamental point.
CHAPTER IX
INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING
MERITS OF LIGHTING BY INCANDESCENT MANTLES.--It has already been shown
that acetylene bases its chief claim for adoption as an illuminant in
country districts upon the fact that, when consumed in simple self-
luminous burners, it gives a light comparable in all respects save that
of cost to the light of incandescent coal-gas. The employment of a mantle
is still accompanied by several objections which appear serious to the
average householder, who is not always disposed either to devote
sufficient attention to his burners to keep them in a high state of
efficiency or to contract for their maintenance by the gas company or
others. Coal-gas cannot be burnt satisfactorily on the incandescent
system unless the glass chimneys and shades are kept clean, unless the
mantles are renewed as soon as they show signs of deterioration, and,
perhaps most important of all, unless the burners are frequently cleared
of the dust which collects round the jets. For this reason luminous
acetylene ranks with luminous coal-gas in convenience and simplicity,
while ranking with incandescent coal-gas in hygienic value. Very similar
remarks apply to paraffin, and, in certain countries, to denatured
alcohol. Since those latter illuminants are also available in rural
places where coal-gas is not laid on, luminous acetylene is a less
advantageous means of procuring artificial light than paraffin (and on
occasion than coal-gas and alcohol when the latter fuels are burnt under
the mantle), if the pecuniary aspect of the question is the only one
considered. Such a comparison, however, is by no means fair; for if coal-
gas, paraffin, and alcohol can be consumed on the incandescent system, so
can acetylene; and if acetylene is hygienically equal to incandescent
coal-gas, it is superior thereto when also burnt under the mantle.
Nevertheless there should be one minor but perfectly irremediable defect
in incandescent acetylene, viz., a sacrifice of that characteristic
property of the luminous gas to emit a light closely resembling that of
the sun in tint, which was mentioned in Chapter 1. Self-luminous
acetylene gives the whitest light hitherto procurable without special
correction of the rays, because its light is derived from glowing
particles of carbon which happen to be heated (because of the high flame
temperature) to the best possible temperature for the emission of pure
white light. The light of any combustible consumed on the "incandescent"
system is derived from glowing particles of ceria, thoria, or similar
metallic oxides; and the character or shade of the light they emit is a
function, apart from the temperature to which they are raised, of their
specific chemical nature. Still, the light of incandescent acetylene is
sufficiently pleasant, and according to Caro is purer white than that of
incandescent coal-gas; but lengthy tests carried out by one of the
authors actually show it to be appreciably inferior to luminous acetylene
for colour-matching, in which the latter is known almost to equal full
daylight, and to excel every form of artificial light except that of the
electric arc specially corrected by means of glass tinted with copper
salts.
CONDITIONS FOR INCANDESCENT ACETYLENE LIGHTING.--For success in the
combustion of acetylene on the incandescent system, however, several
points have to be observed. First, the gas must be delivered at a
strictly constant pressure to the burner, and at one which exceeds a
certain limit, ranging with different types and different sizes of burner
from 2 to 4 or 5 inches of water. (The authors examined, as long ago as
1903, an incandescent burner of German construction claimed to work at a
pressure of 1.5 inches, which it was almost impossible to induce to fire
back to the jets however slowly the cock was manipulated, provided the
pressure of the gas was maintained well above the point specified. But
ordinarily a pressure of about 4 inches is used with incandescent
acetylene burners.) Secondly, it is necessary that the acetylene shall at
all times be free from appreciable admixture with air, even 0.5 per cent,
being highly objectionable according to Caro; so that generators
introducing any noteworthy amount of air into the holder each time their
decomposing chambers are opened for recharging are not suitable for
employment when incandescent burners are contemplated. The reason for
this will be more apparent later on, but it depends on the obvious fact
that if the acetylene already contains an appreciable proportion of air,
when a further quantity is admitted at the burner inlets, the gaseous
mixture contains a higher percentage of oxygen than is suited to the size
and design of the burner, so that flashing back to the injector jets is
imminent at any moment, and may be determined by the slightest
fluctuation in pressure--if, indeed, the flame will remain at the proper
spot for combustion at all. Thirdly, the fact that the acetylene which is
to be consumed under the mantle must be most rigorously purified from
phosphorus compounds has been mentioned in Chapter V. Impure acetylene
will often destroy a mantle in two or three hours; but with highly
purified gas the average life of a mantle may be taken, according to
Giro, at 500 or 600 hours. It is safer, however, to assume a rather
shorter average life, say 300 to 400 burning hours. Fourthly, owing to
the higher pressure at which acetylene must be delivered to an
incandescent burner and to the higher temperature of the acetylene flame
in comparison with coal-gas, a mantle good enough to give satisfactory
results with the latter does not of necessity answer with acetylene; in
fact, the authors have found that English Welsbach coal-gas mantles of
the small sizes required by incandescent acetylene burners are not
competent to last for more than a very few hours, although, in identical
conditions, mantles prepared specially for use with acetylene have proved
durable. The atmospheric acetylene flame, too, differs in shape from an
atmospheric flame of coal-gas, and it does not always happen that a coal-
gas mantle contracts to fit the former; although it usually emits a
better light (because it fits better) after some 20 hours use than at
first. Caro has stated that to derive the best results a mantle needs to
contain a larger proportion of ceria than the 1 per cent. present in
mantles made according to the Welsbach formula, that it should be
somewhat coarser in mesh, and have a large orifice at the head. Other
authorities hold that mantles for acetylene, should contain other rare
earths besides the thoria and ceria of which the coal-gas mantles almost
wholly consist. It seems probable, however, that the composition of the
ordinary impregnating fluid need not be varied for acetylene mantles
provided it is of the proper strength and the mantles are raised to a
higher temperature in manufacture than coal-gas mantles by the use of
either coal-gas at very high pressure or an acetylene flame. The
thickness of the substance of the mantle cannot be greatly increased with
a view to attaining greater stability without causing a reduction in the
light afforded. But the shape should be such that the mantle conforms as
closely as possible to the acetylene Bunsen flame, which differs slightly
with different patterns of incandescent burner heads. According to L.
Cadenel, the acetylene mantle should be cylindrical for the lower two-
thirds of its length, and slightly conical above, with an opening of
moderate size at the top. The head of the mantle should be of slighter
construction than that of coal-gas mantles. Fifthly, generators belonging
to the automatic variety, which in most forms inevitably add more or less
air to the acetylene every time they are cleaned or charged, appear to
have achieved most popularity in Great Britain; and these frequently do
not yield a gas fit for use with the mantle. This state of affairs, added
to what has just been said, makes it difficult to speak in very
favourable terms of the incandescent acetylene light for use in Great
Britain. But as the advantages of an acetylene not contaminated with air
are becoming more generally recognised, and mantles of several different
makes are procurable more cheaply, incandescent acetylene is now more
practicable than hitherto. Carburetted acetylene or "carburylene," which
is discussed later, is especially suitable for use with mantle burners.
ATMOSPHERIC ACETYLENE BURNERS.--The satisfactory employment of acetylene
in incandescent burners, for boiling, warming, and cooking purposes, and
also to some extent as a motive power in small engines, demands the
production of a good atmospheric or non-luminous flame, _i.e._, the
construction of a trustworthy burner of the Bunsen type.
This has been exceedingly difficult to achieve for two reasons: first,
the wide range over which mixtures of acetylene and air are explosive;
secondly, the high speed at which the explosive wave travels through such
a mixture. It has been pointed out in Chapter VIII. that a Bunsen burner
is one in which a certain proportion of air is mixed with the gas before
it arrives at the actual point of ignition; and as that proportion must
be such that the mixture falls between the upper and lower limits of
explosibility, there is a gaseous mixture in the burner tube between the
air inlets and the outlet which, if the conditions are suitable, will
burn with explosive force: that is to say, will fire back to the air jets
when a light is applied to the proper place for combustion. Such an
explosion, of course, is far too small in extent to constitute any danger
to person or property; the objection to it is simply that the shock of
the explosion is liable to fracture the fragile incandescent mantle,
while the gas, continuing to burn within the burner tube (in the case of
a warming or cooking stove), blocks up that tube with carbon, and
exhibits the other well-known troubles of a coal-gas stove which has
"fired back."
It has been shown, however, in Chapter VI. that the range over which
mixtures of acetylene and air are explosive depends on the size of the
vessel, or more particularly on the diameter of the tube, in which they
are stored; so that if the burner tube between the air inlets and the
point of ignition can be made small enough in diameter, a normally
explosive mixture will cease to exhibit explosive properties. Manifestly,
if a tube is made very small in diameter, it will only pass a small
volume of gas, and it may be useless for the supply of an atmospheric
burner; but Le Chatelier's researches have proved that a tube may be
narrowed at one spot only, in such fashion that the explosive wave
refuses to pass the constriction, while the virtual diameter of the tube,
as far as passage of gas is concerned, remains considerably larger than
the size of the constriction itself. Moreover, inasmuch as the speed of
propagation of the explosion is strictly fixed by the conditions
prevailing, if the speed at which the mixture, of acetylene and air
travels from the air inlets to the point of ignition is more rapid than
the speed at which the explosion tends to travel from the point of
ignition to the air inlets, the said mixture of acetylene and air will
burn quietly at the orifice without attempting to fire backwards into the
tube. By combining together these two devices: by delivering the
acetylene to the injector jet at a pressure sufficient to drive the
mixture of gas and air forward rapidly enough, and by narrowing the
leading tube either wholly or at one spot to a diameter small enough, it
is easy to make an atmospheric burner for acetylene which behaves
perfectly as long as it is fairly alight, and the supply of gas is not
checked; but further difficulties still remain, because at the instant of
lighting and extinguishing, i.e., while the tap is being turned on or
off, the pressure of the gas is too small to determine a flow of
acetylene and air within the tube at a speed exceeding that of the
explosive wave; and therefore the act of lighting or extinguishing is
very likely to be accompanied by a smart explosion severe enough to split
the mantle, or at least to cause the burner to fire back. Nevertheless,
after several early attempts, which were comparative failures,
atmospheric acetylene burners have been constructed that work quite
satisfactorily, so that the gas has become readily available for use
under the mantle, or in heating stoves. Sometimes success has been
obtained by the employment of more than one small tube leading to a
common place of ignition, sometimes by the use of two or more fine wire-
gauze screens in the tube, sometimes by the addition of an enlarged head
to the burner in which head alone thorough mixing of the gas and air
occurs, and sometimes by the employment of a travelling sleeve which
serves more or less completely to block the air inlets.
DUTY OF INCANDESCENT ACETYLENE BURNERS.--Granting that the petty troubles
and expenses incidental to incandescent lighting are not considered
prohibitive--and in careful hands they are not really serious--
and that mantles suitable for acetylene are employed, the gas may be
rendered considerably cheaper to use per unit of light evolved by
consuming it in incandescent burners. In Chapter VIII. it was shown that
the modern self-luminous, l/2-foot acetylene burner emits a light of
about 1.27 standard English candles per litre-hour. A large number of
incandescent burners, of German and French construction, consuming from
7.0 to 22.2 litres per hour at pressures ranging between 60 and 120
millimetres have been examined by Caro, who has found them to give lights
of from 10.8 to 104.5 Hefner units, and efficiencies of from 2.40 to 5.50
units per litre-hour. Averaging his results, it may be said that
incandescent burners consuming from 10 to 20 litres per hour at pressures
of 80 or 100 millimetres yield a light of 4.0 Hefner units per litre-
hour. Expressed in English terms, incandescent acetylene burners
consuming 0.5 cubic foot per hour at a pressure of 3 or 4 inches give the
duties shown in the following table, which may advantageously be compared
with that printed in Chapter VIII., page 239, for the self-luminous gas:
ILLUMINATING POWER OF INCANDESCENT ACETYLENE.
HALF-FOOT BURNERS.
1 litre = 3.65 candles | 1 candle = 0.274 litre.
1 cubic foot = 103.40 candles. | 1 candle = 0.0097 cubic foot.
A number of tests of the Guentner or Schimek incandescent burners of the
10 and 15 litres-per-hour sizes, made by one of the authors in 1906, gave
the following average results when tested at a pressure of 4 inches:
_________________________________________________________________
| | | | |
| Nominal size | Rate of Consumption per | Light in | Duty |
| of Burner. | Hour | Candles | Candles per |
| | | | Cubic Foot |
|______________|_________________________|__________|_____________|
| | | | | |
| Litres. | Cubic Foot | Litres | | |
| 10 | 0.472 | 13.35 | 46.0 | 97.4 |
| 15 | 0.663 | 18.80 | 70.0 | 105.5 |
|______________|____________|____________|__________|_____________|
These figures indicate that the duty increases slightly with the size of
the burner. Other tests showed that the duty increased more considerably
with an increase of pressure, so that mantles used, or which had been
previously used, at a pressure of 5 inches gave duties of 115 to 125
candles per cubic foot.
It should be noted that the burners so far considered are small, being
intended for domestic purposes only; larger burners exhibit higher
efficiencies. For instance, a set of French incandescent acetylene
burners examined by Fouche showed:
_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 20 | 5.9 | 0.71 | 70 | 98.6 |
| 40 | 5.9 | 1.41 | 150 | 106.4 |
| 70 | 5.9 | 2.47 | 280 | 113.4 |
| 120 | 5.9 | 4.23 | 500 | 118.2 |
|________________|__________|____________|__________|_____________|
By increasing the pressure at which acetylene is introduced into burners
of this type, still larger duties may be obtained from them:
_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 55 | 39.4 | 1.94 | 220 | 113.4 |
| 100 | 39.4 | 3.53 | 430 | 121.8 |
| 180 | 39.4 | 6.35 | 820 | 129.1 |
| 260 | 27.6 | 9.18 | 1300 | 141.6 |
|________________|__________|____________|__________|_____________|
High-power burners such as these are only fit for special purposes, such
as lighthouse illumination, or optical lantern work, &c.; and they
naturally require mantles of considerably greater tenacity than those
intended for employment with coal-gas. Nevertheless, suitable mantles can
be, and are being, made, and by their aid the illuminating duty of
acetylene can be raised from the 30 odd candles per foot of the common
0.5-foot self-luminous jet to 140 candles or more per foot, which is a
gain in efficiency of 367 per cent., or, neglecting upkeep and sundries
and considering only the gas consumed, an economy of nearly 79 per cent.
In 1902, working apparently with acetylene dissolved under pressure in
acetone (_cf._ Chapter XI.), Lewes obtained the annexed results with
the incandescent gas:
________________________________________________________
| | | | |
| Pressure. | Cubic Feet | Candle Power | Candles per |
| Inches. | per Hour. | Developed. | Cubic Foot. |
|___________|_____________|______________|______________|
| | | | |
| 8 | 0.883 | 65 | 73.6 |
| 9 | 0.94 | 72 | 76.0 |
| 10 | 1.00 | 146 | 146.0 |
| 12 | 1.06 | 150 | 141.2 |
| 15 | 1.25 | 150 | 120.0 |
| 20 | 1.33 | 166 | 124.8 |
| 25 | 1.50 | 186 | 123.3 |
| 40 | 2.12 | 257 | 121.2 |
|___________|_____________|______________|______________|
It will be seen that although the total candle-power developed increases
with the pressure, the duty of the burner attained a maximum at a
pressure of 10 inches. This is presumably due to the fact either that the
same burner was used throughout the tests, and was only intended to work
at a pressure of 10 inches or thereabouts, or that the larger burners
were not so well constructed as the smaller ones. Other investigators
have not given this maximum of duty with a medium-sized or medium-driven
burner; but Lewes has observed a similar phenomenon in the case of 0.7 to
0.8 cubic foot self-luminous jets.
Figures, however, which seem to show that the duty of incandescent
acetylene does not always rise with the size of the burner or with the
pressure at which the gas is delivered to it, have been published in
connexion with the installation at the French lighthouse at Chassiron,
the northern point of the Island of Oleron. Here the acetylene is
generated in hand-fed carbide-to-water generators so constructed as to
give any pressure up to nearly 200 inches of water column; purified by
means of heratol, and finally delivered to a burner composed of thirty-
seven small tubes, which raises to incandescence a mantle 55 millimetres
in diameter at its base. At a pressure of 7.77 inches of water, the
burner passes 3.9 cubic feet of acetylene per hour, and at a pressure of
49.2 inches (the head actually used) it consumes 20.06 cubic feet per
hour. As shown by the following table, such increment of gas pressure
raises the specific intensity of the light, _i.e._, the illuminating
power per unit of incandescent surface, but it does not appreciably raise
the duty or economy of the gas. Manifestly, in terms of duty alone, a
pressure of 23.6 inches of water-column is as advantageous as the higher
Chassiron figures; but since intensity of light is an important matter in
a lighthouse, it is found better on the whole to work the generators at a
pressure of 49.2 inches. In studying these figures referring to the
French lighthouse, it is interesting to bear in mind that when ordinary
six-wick petroleum oil burners wore used in the same place, the specific
intensity of the light developed was 75 candle-power per square inch, and
when that plant was abandoned in favour of an oil-gas apparatus, the
incandescent burner yielded 161 candle-power per square inch;
substitution of incandescent acetylene under pressure has doubled the
brilliancy of the light.
___________________________________________________________
| | | |
| | Duty. | Intensity. |
| Pressure in Inches. | Candle-power per | Candle-power per |
| | Cubic Foot. | Square Inch. |
|_____________________|__________________|__________________|
| | | |
| 7.77 | 105.5 | 126.0 |
| 23.60 | 106.0 | 226.0 |
| 31.50 | 110.0 | 277.0 |
| 39.40 | 110.0 | 301.0 |
| 47.30 | 106.0 | 317.0 |
| 49.20 | 104.0 | 324.9 |
| 196.80 | 110.0 | 383.0 |
|_____________________|__________________|__________________|
When tested in modern burners consuming between 12 and 18 litres per hour
at a pressure of 100 millimetres (4 inches), some special forms of
incandescent mantles constructed of ramie fibre, which in certain
respects appears to be better suited than cotton for use with acetylene,
have shown the following degree of loss in illuminating power after
prolonged employment (Caro):
_Luminosity in Hefner Units._
________________________________________________________
| | | | | |
| Mantle. | New. | After | After | After |
| | | 100 Hours. | 200 Hours. | 400 Hours. |
|_________|_______|____________|____________|____________|
| | | | | |
| No. 1. | 53.2 | 51.8 | 50.6 | 49.8 |
| No. 2. | 76.3 | 75.8 | 73.4 | 72.2 |
| No. 3. | 73.1 | 72.5 | 70.1 | 68.6 |
|_________|_______|____________|____________|____________|
It will be seen that the maximum loss of illuminating power in 400 hours
was 6.4 per cent., the average loss being 6.0 per cent.
TYPICAL INCANDESCENT BURNERS.--Of the many burners for lighting by the
use of incandescent mantles which have been devised, a few of the more
widely used types may be briefly referred to. There is no doubt that
finality in the design of these burners has not yet been reached, and
that improvements in the direction of simplification of construction and
in efficiency and durability will continue to be made.
Among the early incandescent burners, one made by the Allgemeine Carbid
und Acetylen Gesellschaft of Berlin in 1900 depended on the narrowness of
the mixing tube and the proportioning of the gas nipple and air inlets to
prevent lighting-back. There was a wider concentric tube round the upper
part of the mixing tube, and the lower part of the mantle fitted round
this. The mouth of the mixing tube of this 10-litres-per-hour burner was
0.11 inch in diameter, and the external diameter of the middle
cylindrical part of the mixing tube was 0.28 inch. There was no gauze
diaphragm or stuffing, and firing-back did not occur until the pressure
was reduced to about 1.5 inches. The same company later introduced a
burner differing in several important particulars from the one just
described. The comparatively narrow stem of the mixing tube and the
proportions of the gas nipple and air inlets were retained, but the
mixing tube was surmounted by a wide chamber or burner head, in which
naturally there was a considerable reduction in the rate of flow of the
gas. Consequently it was found necessary to introduce a gauze screen into
the burner head to prevent firing back. The alterations have resulted in
the lighting duty of the burner being considerably improved. Among other
burners designed about 1900 may be mentioned the Ackermann, the head of
which consisted of a series of tubes from each of which a jet of flame
was produced, the Fouche, the Weber, and the Trendel. Subsequently a
tubular-headed burner known as the Sirius has been produced for the
consumption of acetylene at high pressure (20 inches and upwards).
The more recent burners which have been somewhat extensively used include
the "Schimek," made by W. Guentner of Vienna, which is shown in Fig. 19.
It consists of a tapering narrow injecting nozzle within a conical
chamber C which is open below, and is surmounted by the mixing tube over
which telescopes a tube which carries the enlarged burner head G, and the
chimney gallery D. There are two diaphragms of gauze in the burner head
to prevent firing back, and one in the nozzle portion of the burner. The
conical chamber has a perforated base-plate below which is a circular
plate B which rotates on a screw cut on the lower part of the nozzle
portion A of the burner. This plate serves as a damper to control the
amount of air admitted through the base of the conical chamber to the
mixing tube. There are six small notches in the lower edge of the conical
chamber to prevent the inflow of air being cut of entirely by the damper.
The mixing tube in both the 10-litre and the 15-litre burner is about
0.24 inch in internal diameter but the burner head is nearly 0.42 inch in
the 10-litre and 0.48 inch in the 15-litre burner. The opening in the
head of the burner through which the mixture of gas and air escapes to
the flame is 0.15 and 0.17 inch in diameter in these two sizes
respectively. The results of some testings made with Schimek burners have
been already given.
[Illustration: FIG. 19.--"SCHIMEK" BURNER.]
The "Knappich" burner, made by the firm of Keller and Knappich of
Augsburg, somewhat resembles the later pattern of the Allgemeine Carbid
und Acetylen Gesellschaft. It has a narrow mixing tube, viz., 0.2 inch in
internal diameter, and a wide burner head, viz., 0.63 inch in internal
diameter for the 25-litre size. The only gauze diaphragm is in the upper
part of the burner head. The opening in the cap of the burner head, at
which the gas burns, is 0.22 inch in diameter. The gas nipple extends
into a domed chamber at the base of the mixing tube, and the internal air
is supplied through four holes in the base-plate of that chamber. No
means of regulating the effective area of the air inlet holes are
provided.
The "Zenith" burner, made by the firm of Gebrueder Jacob of Zwickau, more
closely resembles the Schimek, but the air inlets are in the side of the
lower widened portion of the mixing tube, and are more or less closed by
means of an outside loose collar which may be screwed up and down on a
thread on a collar fixed to the mixing tube. The mixing tube is 0.24
inch, and the burner head 0.475 inch in internal diameter. The opening in
the cap of the burner is 0.16 inch in diameter. There is a diaphragm of
double gauze in the cap, and this is the only gauze used in the burner.
All the incandescent burners hitherto mentioned ordinarily have the gas
nipple made in brass or other metal, which is liable to corrosion, and
the orifice to distortion by heat or if it becomes necessary to remove
any obstruction from it. The orifice in the nipple is extremely small--
usually less than 0.015 inch--and any slight obstruction or distortion
would alter to a serious extent the rate of flow of gas through it, and
so affect the working of the burner. In order to overcome this defect,
inherent to metal nipples, burners are now constructed for acetylene in
which the nipple is of hard incorrodible material. One of these burners
has been made on behalf of the Office Central de l'Acetylene of Paris,
and is commonly known as the "O.C.A." burner. In it the nipple is of
steatite. On the inner mixing tube of this burner is mounted an elongated
cone of wire wound spirally, which serves both to ensure proper admixture
of the gas and air, and to prevent firing-back. There is no gauze in this
burner, and the parts are readily detachable for cleaning when required.
Another burner, in which metal is abolished for the nipple, is made by
Geo. Bray and Co., Ltd., of Leeds, and is shown in Fig. 20. In this
burner the injecting nipple is of porcelain.
[Illustration: FIG. 20.--BRAY'S INCANDESCENT BURNER.]
ACETYLENE FOR HEATING AND COOKING.--Since the problem of constructing a
trustworthy atmospheric burner has been solved, acetylene is not only
available for use in incandescent lighting, but it can also be employed
for heating or cooking purposes, because all boiling, most warming, and
some roasting stoves are simply arrangements for utilising the heat of a
non-luminous flame in one particular way. With suitable alterations in
the dimensions of the burners, apparatus for consuming coal-gas may be
imitated and made fit to burn acetylene; and as a matter of fact several
firms are now constructing such appliances, which leave little or nothing
to be desired. It may perhaps be well to insist upon the elementary point
which is so frequently ignored in practice, viz., that no stove, except
perhaps a small portable boiling ring, ought ever to be used in an
occupied room unless it is connected with a chimney, free from down-
draughts, for the products of combustion to escape into the outer air;
and also that no chimney, however tall, can cause an up-draught in all
states of the weather unless there is free admission of fresh air into
the room at the base of the chimney. Still, at the prices for coal,
paraffin oil, and calcium carbide which exist in Great Britain, acetylene
is not an economical means of providing artificial heat. If a 0.7 cubic
foot luminous acetylene burner gives a light of 27 candles, and if
ordinary country coal-gas gives light of 12 to 13 candles in a 5-foot
burner, one volume of acetylene is equally valuable with 15 or 16 volumes
of coal-gas when both are consumed in self-luminous jets; and if, with
the mantle, acetylene develops 99 candles per cubic foot, while coal-gas
gives in common practice 15 to 20 candles, one volume of acetylene is
equally valuable with 5 to 6-1/2 volumes of coal-gas when both are
consumed on the incandescent system; whereas, if the acetylene is burnt
in a flat flame, and the coal-gas under the mantle, 1 volume of the
former is equally efficient with 2 volumes of coal-gas as an artificial
illuminant. This last method of comparison being manifestly unfair,
acetylene may be said to be at least five times as efficient per unit of
volume as coal-gas for the production of light. But from the table given
on a later page it appears that as a source of artificial heat, acetylene
is only equal to about 2-3 times its volume of ordinary coal-gas.
Nevertheless, the domestic advantages of gas firing are very marked; and
when a properly constructed stove is properly installed, the hygienic
advantages of gas-firing are alone equally conspicuous--for the disfavor
with which gas-firing is regarded by many physicians is due to experience
gained with apparatus warming principally by convection [Footnote:
Radiant heat is high-temperature heat, like the heat emitted by a mass of
red-hot coke; convected heat is low-temperature heat, invisible to the
eye. Radiant heat heats objects first, and leaves them to warm the air;
convected heat is heat applied directly to air, and leaves the air to
warm objects afterwards. On all hygienic grounds radiant heat is better
than convected heat, but the latter is more economical. By an absurd and
confusing custom, that particular warming apparatus (gas, steam, or hot
water) which yields practically no radiant heat, and does all its work by
convection, is known to the trade as a "radiator."] instead of radiation;
or to acquaintance with intrinsically better stoves either not connected
to any flues or connected to one deficient in exhausting power. In these
circumstances, whenever an installation of acetylene has been laid down
for the illumination of a house or district, the merit of convenience may
outweigh the defect of extravagance, and the gas may be judiciously
employed in a boiling ring, or for warming a bedroom; while, if pecuniary
considerations are not paramount, the acetylene may be used for every
purpose to which the townsman would apply his cheaper coal-gas.
The difficulty of constructing atmospheric acetylene burners in which the
flame would not be likely to strike back to the nipple has already been
referred to in connexion with the construction atmospheric burners for
incandescent lighting. Owing, however, to the large proportions of the
atmospheric burners of boiling rings and stove and in particular to the
larger bore of their mixing tube, the risk of the flame striking back is
greater with them, than with incandescent lighting burners. The greatest
trouble is presented at lighting, and when the pressure of the gas-supply
is low. The risk of firing-back when the burner is lighted is avoided in
some forms of boiling rings, &c., by providing a loose collar which can
be slipped over the air inlets of the Bunsen tube before applying a light
to the burner, and slipped clear of them as soon as the burner is alight.
Thus at the moment of lighting, the burner is converted temporarily into
one of the non-atmospheric type, and after the flame has thus been
established at the head or ring of the burner, the internal air-supply is
started by removing the loose collar from the air inlets, and the flame
is thus made atmospheric. In these conditions it does not travel
backwards to the nipple. In other heating burners it is generally
necessary to turn on the gas tap a few seconds before applying a light to
the burner or ring or stove; the gas streaming through the mixing tube
then fills it with acetylene and air mixed in the proper working
proportions, and when the light is applied, there is no explosion in the
mixing tube, or striking-back of the flame to the nipple.
Single or two-burner gas rings for boiling purposes, or for heating
cooking ovens, known as the "La Belle," made by Falk Stadelmann and Co.,
Ltd., of London, may be used at as low a gas pressure as 2 inches, though
they give better results at 3 inches, which is their normal working
pressure. The gas-inlet nozzle or nipple of the burner is set within a
spherical bulb in which are four air inlets. The mixing tube which is
placed at a proper distance in front of the nipple, is proportioned to
the rate of flow of the gas and air, and contains a mixing chamber with a
baffling pillar to further their admixture. A fine wire gauze insertion
serves to prevent striking-back of the flame. A "La Belle" boiling ring
consumes at 3 inches pressure about 48 litres or 1.7 cubic feet of
acetylene per hour.
ACETYLENE MOTORS.--The question as to the feasibility of developing
"power" from acetylene, _i.e._, of running an engine by means of the
gas, may be answered in essentially identical terms. Specially designed
gas-engines of 1, 3, 6, or even 10 h.p. work perfectly with acetylene,
and such motors are in regular employment in numerous situations, more
particularly for pumping water to feed the generators of a large village
acetylene installation. Acetylene is not an economical source of power,
partly for the theoretical reason that it is a richer fuel even than
coal-gas, and gas-engines would appear usually to be more efficient as
the fuel they burn is poorer in calorific intensity, _i.e._, in
heating power (which is explosive power) per unit of volume. The richer,
or more concentrated, any fuel in, the more rapidly does the explosion in
a mixture of that fuel with air proceed, because a rich fuel contains a
smaller proportion of non-inflammable gases which tend to retard
explosion than a poor one; and, in reason, a gas-engine works better the
more slowly the mixture of gas and air with which it is fed explodes.
Still, by properly designing the ports of a gas-engine cylinder, so that
the normal amount of compression of the charge and of expansion of the
exploded mixture which best suit coal-gas are modified to suit acetylene,
satisfactory engines can be constructed; and wherever an acetylene
installation for light exists, it becomes a mere question of expediency
whether the same fuel shall not be used to develop power, say, for
pumping up the water required in a large country house, instead of
employing hand labour, or the cheaper hot-air or petroleum motor. Taking
the mean of the results obtained by numerous investigators, it appears
that 1 h.p.-hour can be obtained for a consumption of 200 litres of
acetylene; whence it may be calculated that that amount of energy costs
about 3d. for gas only, neglecting upkeep, lubricating material
(which would be relatively expensive) and interest, &c.
Acetylene Blowpipes--The design of a satisfactory blowpipe for use with
acetylene had at first proved a matter of some difficulty, since the jet,
like that of an ordinary self-luminous burner, usually exhibited a
tendency to become choked with carbonaceous growths. But when acetylene
had become available for various purposes at considerable pressure, after
compression into porous matter as described in Chapter XI, the troubles
were soon overcome; and a new form of blowpipe was constructed in which
acetylene was consumed under pressure in conjunction with oxygen. The
temperature given by this apparatus exceeds that of the familiar oxy-
hydrogen blowpipe, because the actual combustible material is carbon
instead of hydrogen. When 2 atoms of hydrogen unite with 1 of oxygen to
form 1 molecule of gaseous water, about 59 large calories are evolved,
and when 1 atom of solid amorphous carbon unites with 2 atoms of oxygen
to form 1 molecule of carbon dioxide, 97.3 calories are evolved. In both
cases, however, the heat attainable is limited by the fact that at
certain temperatures hydrogen and oxygen refuse to combine to form water,
and carbon and oxygen refuse to form carbon dioxide--in other words,
water vapour and carbon dioxide dissociate and absorb heat in the process
at certain moderately elevated temperatures. But when 1 atom of solid
amorphous carbon unites with 1 atom of oxygen to form carbon monoxide,
29.1 [Footnote: Cf. Chapter VI., page 185.] large calories are produced,
and carbon monoxide is capable of existence at much higher temperatures
than either carbon dioxide or water vapour. In any gaseous hydrocarbon,
again, the carbon exists in the gaseous state, and when 1 atom of the
hypothetical gaseous carbon combines with 1 atom of oxygen to produce 1
molecule of carbon monoxide, 68.2 large calories are evolved. Thus while
solid amorphous carbon emits more heat than a chemically equivalent
quantity of hydrogen provided it is enabled to combine with its higher
proportion of oxygen, it emits less if only carbon monoxide is formed;
but a higher temperature can be attained in the latter case, because the
carbon monoxide is more permanent or stable. Gaseous carbon, on the other
hand, emits more heat than an equivalent quantity of hydrogen, [Footnote:
In a blowpipe flame hydrogen can only burn to gaseous, not liquid,
water.] even when it is only converted into the monoxide. In other words,
a gaseous fuel which consists of hydrogen alone can only yield that
temperature as a maximum at which the speed of the dissociation of the
water vapour reaches that of the oxidation of the hydrogen; and were
carbon dioxide the only oxide of carbon, a similar state of affairs would
be ultimately reached in the flame of a carbonaceous gas. But since in
the latter case the carbon dioxide does not tend to dissociate
completely, but only to lose one atom of oxygen, above the limiting
temperature for the formation of carbon dioxide, carbon monoxide is still
produced, because there is less dissociating force opposed to its
formation. Thus at ordinary temperatures the heat of combustion of
acetylene is 315.7 calories; but at temperatures where water vapour and
carbon dioxide no longer exist, there is lost to that quantity of 315.7
calories the heat of combustion of hydrogen (69.0) and twice that of
carbon monoxide (68.2 x 2 = 136.4); so that above those critical
temperatures, the heat of combustion of acetylene is only 315.7 - (69.0 +
136.4) = 110.3. [Footnote: When the heat of combustion of acetylene is
quoted as 315.7 calories, it is understood that the water formed is
condensed into the liquid state. If the water remains gaseous, as it must
do in a flame, the heat of formation is reduced by about 10 calories.
This does not affect the above calculation, because the heat of
combustion of hydrogen when the water remains gaseous is similarly 10
calories less than 69, _i.e._, 59, as mentioned above in the text.
Deleting the heat of liquefaction of water, the calculation referred to
becomes 305.7 - (59.0 + l36.4) = 110.3 as before.] This value of 110.3
calories is clearly made up of the heat of formation of acetylene itself,
and twice the heat of conversion of carbon into carbon monoxide,
_i.e._, for diamond carbon, 58.1 + 26.1 x 2 = 110.3; or for
amorphous carbon, 52.1 + 29.1 x 2 = 110.3. From the foregoing
considerations, it may be inferred that the acetylene-oxygen blowpipe can
be regarded as a device for burning gaseous carbon in oxygen; but were it
possible to obtain carbon in the state of gas and so to lead it into a
blowpipe, the acetylene apparatus should still be more powerful, because
in it the temperature would be raised, not only by the heat of formation
of carbon monoxide, but also by the heat attendant upon the dissociation
of the acetylene which yields the carbon.
Acetylene requires 2.5 volumes of oxygen to burn it completely; but in
the construction of an acetylene-oxygen blowpipe the proportion of oxygen
is kept below this figure, viz., at 1.1 to 1.8 volumes, so that the
deficiency is left to be made up from the surrounding air. Thus at the
jet of the blowpipe the acetylene dissociates and its carbon is oxidised,
at first no doubt to carbon monoxide only, but afterwards to carbon
dioxide; and round the flame of the gaseous carbon is a comparatively
cool, though absolutely very hot jacket of hydrogen burning to water
vapour in a mixture of oxygen and air, which protects the inner zone from
loss of heat. As just explained, theoretical grounds support the
conclusions at which Fouche has arrived, viz., that the temperature of
the acetylene-oxygen blowpipe flame is above that at which hydrogen will
combine with oxygen to form water, and that it can only be exceeded by
those found in a powerful electric furnace. As the hydrogen dissociated
from the acetylene remains temporarily in the free state, the flame of
the acetylene blowpipe, possesses strong reducing powers; and this,
coupled probably with an intensity of heat which is practically otherwise
unattainable, except by the aid of a high-tension electric current,
should make the acetylene-oxygen blowpipe a most useful piece of
apparatus for a large variety of metallurgical, chemical, and physical
operations. In Fouche's earliest attempts to design an acetylene
blowpipe, the gas was first saturated with a combustible vapour, such as
that of petroleum spirit or ether, and the mixture was consumed with a
blast of oxygen in an ordinary coal-gas blow-pipe. The apparatus worked
fairly well, but gave a flame of varying character; it was capable of
fusing iron, raised a pencil of lime to a more brilliant degree of
incandescence than the eth-oxygen burner, and did not deposit carbon at
the jet. The matter, however, was not pursued, as the blowpipe fed with
undiluted acetylene took its place. The second apparatus constructed by
Fouche was the high-pressure blowpipe, the theoretical aspect of which
has already been studied. In this, acetylene passing through a water-seal
from a cylinder where it is stored as a solution in acetone (_cf._
Chapter XI.), and oxygen coming from another cylinder, are each allowed
to enter the blowpipe at a pressure of 118 to 157 inches of water column
(_i.e._, 8.7 to 11.6 inches of mercury; 4.2 to 5.7 lb. per square
inch, or 0.3 to 0.4 atmosphere). The gases mix in a chamber tightly
packed with porous matter such as that which is employed in the original
acetylene reservoir, and finally issue from a jet having a diameter of 1
millimetre at the necessary speed of 100 to 150 metres per second.
Finding, however, that the need for having the acetylene under pressure
somewhat limited the sphere of usefulness of his apparatus, Fouche
finally designed a low-pressure blowpipe, in which only the oxygen
requires to be in a state of compression, while the acetylene is drawn
directly from any generator of the ordinary pattern that does not yield a
gas contaminated with air. The oxygen passes through a reducing valve to
lower the pressure under which it stands in the cylinder to that of 1 or
1.5 effective atmosphere, this amount being necessary to inject the
acetylene and to give the previously mentioned speed of escape from the
blowpipe orifice. The acetylene is led through a system of long narrow
tubes to prevent it firing-back.
AUTOGENOUS SOLDERING AND WELDING.--The blowpipe is suitable for the
welding and for the autogenous soldering or "burning" of wrought or cast
iron, steel, or copper. An apparatus consuming from 600 to 1000 litres of
acetylene per hour yields a flame whose inner zone is 10 to 15
millimetres long, and 3 to 4 millimetres in diameter; it is sufficiently
powerful to burn iron sheets 8 to 9 millimetres thick. By increasing the
supply of acetylene in proportion to that of the oxygen, the tip of the
inner zone becomes strongly luminous, and the flame then tends to
carburise iron; when the gases are so adjusted that this tip just
disappears, the flame is at its best for heating iron and steel. The
consumption of acetylene is about 75 litres per hour for each millimetre
of thickness in the sheet treated, and the normal consumption of oxygen
is 1.7 times as much; a joint 6 metres long can be burnt in 1 millimetre
plate per hour, and one of 1.5 metres in 10 millimetre plate. In certain
cases it is found economical to raise the metal to dull redness by other
means, say with a portable forge of the usual description, or with a
blowpipe consuming coal-gas and air. There are other forms of low-
pressure blowpipe besides the Fouche, in some of which the oxygen also is
supplied at low pressure. Apart from the use of cylinders of dissolved
acetylene, which are extremely convenient and practically indispensable
when the blowpipe has to be applied in confined spaces (as in repairing
propeller shafts on ships _in situ_), acetylene generators are now
made by several firms in a convenient transportable form for providing
the gas for use in welding or autogenous soldering. It is generally
supposed that the metal used as solder in soldering iron or steel by this
method must be iron containing only a trifling proportion of carbon (such
as Swedish iron), because the carbon of the acetylene carburises the
metal, which is heated in the oxy-acetylene flame, and would thereby make
ordinary steel too rich in carbon. But the extent to which the metal used
is carburised in the flame depends, as has already been indicated, on the
proper adjustment of the proportion of oxygen to acetylene. Oxy-acetylene
autogenous soldering or welding is applicable to a great variety of work,
among which may be mentioned repairs to shafts, locomotive frames,
cylinders, and to joints in ships' frames, pipes, boilers, and rails. The
use of the process is rapidly extending in engineering works generally.
Generators for acetylene soldering or welding must be of ample size to
meet the quickly fluctuating demands on them and must be provided with
water-seals, and a washer or scrubber and filter capable of arresting all
impurities held mechanically in the crude gas, and with a safety vent-
pipe terminating in the open at a distance from the work in hand. The
generator must be of a type which affords as little after-generation as
possible, and should not need recharging while the blowpipe is in use.
There should be a main tap on the pipe between the generator and the
blowpipe. It does not appear conclusively established that the gas
consumed should have been chemically purified, but a purifier of ample
size and charged with efficient material is undoubtedly beneficial. The
blowpipe must be designed so that it remains sufficiently cool to prevent
polymerisation of the acetylene and deposition of the resultant particles
of carbon or soot within it.
It is important to remember that if a diluent gas, such as nitrogen, is
present, the superior calorific power of acetylene over nearly all gases
should avail to keep the temperature of the flame more nearly up to the
temperature at which hydrogen and oxygen cease to combine. Hence a
blowpipe fed with air and acetylene would give a higher temperature than
any ordinary (atmospheric) coal-gas blowpipe, just as, as has been
explained in Chapter VI., an ordinary acetylene flame has a higher
temperature than a coal-gas flame. It is likely that a blowpipe fed with
"Linde-air" (oxygen diluted with less nitrogen than in the atmosphere)
and acetylene would give as high a limelight effect as the oxy-hydrogen
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