Scientific American Supplement, No. 433, April 19, 1884
by
Various
Part 1 out of 2
Produced by J. Niehof, D. Kretz, J. Sutherland, and Distributed Proofreaders
[Illustration]
SCIENTIFIC AMERICAN SUPPLEMENT NO. 433
NEW YORK, APRIL 19, 1884
Scientific American Supplement. Vol. XVII, No. 433.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
* * * * *
TABLE OF CONTENTS.
I. CHEMISTRY, METALLURGY, ETC.--New Analogy between
Solids, Liquids, and Gases.
Hydrogen Amalgam.
Treatment of Ores by Electrolysis.--By M. KILIANI.
II. ENGINEERING, AND MECHANICS.--Electric Railway at Vienna.--With
engraving.
Instruction in Mechanical Engineering.--Technical and trade
education.--A course of study sketched out.--By Prof. R.H.
THURSTON.
Improved Double Boiler.--3 figures.
The Gardner Machine Gun.--With three engravings showing the
single barrel, two barrel, and five barrel guns.
Climbing Tricycles.
Submarine Explorations.--Voyage of the Talisman.--The Thibaudier
sounding apparatus.--With map, diagrams, and engravings.
Jamieson's Cable Grapnel.--With engraving.
A Threaded Set Collar.
III. TECHNOLOGY.--Wretched Boiler Making.
Pneumatic Malting.--With full description of the most improved
methods and apparatus.--Numerous figures.
Reducing and Enlarging Plaster Casts.
Stripping the Film from Gelatine Negatives.
IV. ELECTRICITY.--Non-sparking Key.
New Instruments for Measuring Electric Currents and Electromotive
Force.--By MESSRS. K.E. CROMPTON and GISBERT
KAPP.--Paper read before the Society of Telegraph Engineers.--With
several engravings.
When Does the Electric Shock Become Fatal?
V. ART AND ARCHAEOLOGY.--Robert Cauer's Statute of Lorelei.--With
engraving.
The Pyramids of Meroe.--With engraving.
VI. ASTRONOMY AND METEOROLOGY.--The Red Sky.--Cause of
the same explained by the Department of Meteorology.
A Theory of Cometary Phenomena.
On Comets.--By FURMAN LEAMING, M.D.
VII. NATURAL HISTORY.--The Prolificness of the Oyster.
Coarse Food for Pigs.
VIII. BOTANY, HORTICULTURE, ETC.--Forms of Ivy.--With
several engravings.
Propagating Roses.
A Few of the Best Inulas.--With engraving.
Fruit Growing.--By P.H. FOSTER.
IX. MEDICINE, HYGIENE, ETC.--A People without Consumption,
and Some Account of Their Country, the Cumberland Tableland.
--By E.M. WIGHT.
The Treatment of Habitual Constipation.
X. MISCELLANEOUS.--The French Scientific Station at Cape Horn.
XI. BIOGRAPHY.--The Late Maori Chief, Mete Kingi.--With portrait.
* * * * *
THE FRENCH SCIENTIFIC STATION AT CAPE HORN.
In 1875 Lieutenant Weyprecht of the Austrian navy called the attention
of scientific men to the desirability of having an organized and
continual system of hourly meteorological and magnetic observations
around the poles. In 1879 the first conference of what was termed the
International Polar Congress was held at Hamburg. Delegates from eight
nations were present--Germany, Austria, Denmark, France, Holland,
Norway, Russia, and Sweden.
The congress then settled upon a programme whose features were: 1. To
establish general principles and fixed laws in regard to the pressure
of the atmosphere, the distribution and variation of temperature,
atmospheric currents, climatic characteristics. 2. To assist the
prediction of the course and occurrence of storms. 3. To assist the
study of the disturbances of the magnetic elements and their relations
to the auroral light and sun spots. 4. To study the distribution of
the magnetic force and its secular and other changes. 5. To study the
distribution of heat and submarine currents in the polar regions. 6. To
obtain certain dimensions in accord with recent methods. Finally, to
collect observations and specimens in the domain of zoology, botany,
geology, etc.
The representatives of the various nations had several conferences
later, and by the 1st of May, 1881, there were sufficient subscribers to
justify the establishment of eight Arctic stations.
France entered actively in this work later, and its first expedition was
to Orange Bay and Cape Horn, under the surveillance and direction of
the Academy of Sciences, Paris, and responsible to the Secretary of the
Navy. On the 6th of September, 1882, this scientific corps established
itself in Orange Bay, near Cape Horn, and energetically began its
serious labors, and by October 22 the greater part of their preliminary
preparations was completed, comprising the erection of a magnetic
observatory, an astronomic observatory, a room for the determination of
the carbonic anhydride of the air, another for the sea register, and
a bridge 92 feet long, photographic laboratory, barometer room, and
buildings for the men, food, and appurtenances, together with a
laboratory of natural history.
In short, in spite of persistent rains and the difficulties of the
situation, from September 8 to October 22 they erected an establishment
of which the different parts, fastened, as it were, to the flank of a
steep hill, covered 450 square meters (4,823 square feet), and rested
upon 200 wooden piles.
From September 26, 1882, to September 1, 1883, night and day
uninterruptedly, a watch was kept, in which the officers took part, so
that the observations might be regularly made and recorded. Every four
hours a series of direct magnetic and meteorological observations was
made, from hour to hour meteorological notes were taken, the rise and
fall of the sea recorded, and these were frequently multiplied by
observations every quarter of an hour; the longitude and latitude were
exactly determined, a number of additions to the catalogue of the fixed
stars for the southern heavens made, and numerous specimens in natural
history collected.
The apparatus employed by the expedition for the registration of the
magnetic elements was devised by M. Mascart, by which the variations
of the three elements are inscribed upon a sheet of paper covered with
gelatine bromide, inclination, vertical and horizontal components, with
a certainty which is shown by the 330 diurnal curves brought back from
the Cape.
The register proper is composed of a clock and a photographic frame
which descends its entire length in twenty-four hours, thus causing the
sensitized paper to pass behind a horizontal window upon which falls the
light reflected by the mirrors of the magnetic instruments. One of those
mirrors is fixed, and gives a line of reference; the other is attached
to the magnetic bar, whose slightest movements it reproduces upon the
sensitized paper. The moments when direct observations were taken were
carefully recorded. The magnetic _pavilion_ was made of wood and copper,
placed at about fifty-three feet from the dwellings or camp, near the
sea, against a wooded hill which shaded it completely; the interior
was covered with felt upon all its sides, in order to avoid as much as
possible the varying temperatures.
The diurnal amplitude of the declination increased uniformly from the
time of their arrival in September up to December, when it obtained
its maximum of 7'40", then diminished to June, when it is no more than
2'20"; from this it increased up to the day of departure. The maximum
declination takes place toward 1 P.M., the minimum at 8:50 A.M. The
night maxima and minima are not clearly shown except in the southern
winter.
The mean diurnal curve brings into prominence the constant diminution
of the declination and the much greater importance of the perturbations
during the summer months. These means, combined with the 300 absolute
determinations, give 4' as the annual change of the declination.
M. Mascart's apparatus proved to be wonderfully useful in recording the
rapid and slight perturbations of the magnet. Comparisons between the
magnetic and atmospheric perturbations gave no result. There was,
however, little stormy weather and no auroral displays. This latter
phenomenon, according to the English missionaries, is rarely observed in
Tierra del Fuego.
The electrometer used at the Cape was founded upon the principle
developed by Sir William Thomson. The atmospheric electricity is
gathered up by means of a thin thread of water, which flows from a
large brass reservoir furnished with a metallic tube 6.5 feet long. The
reservoir is placed upon glass supports isolated by sulphuric acid, and
is connected to the electrometer by a thread of metal which enters a
glass vessel containing sulphuric acid; into the same vessel enters a
platinum wire coming from the aluminum needle. Only 3,000 observations
were given by the photographic register, due to the fact that the
instruments were not fully protected against constant wet and cold.
Besides these observations direct observations of the magnetometer were
made, and the absolute determination of the elements of terrestrial
magnetism attempted.
On the 17th of November, 1882, a severe magnetic disturbance occurred,
lasting from 12 M. until 3 P.M., which in three hours changed the
declination 42'. The same perturbation was felt in Europe, and the
comparison of the observations in the two hemispheres will prove
instructive.
* * * * *
THE ELECTRIC RAILWAY AT VIENNA.
The total length of this railway, which extended from the Eiskeller in
the Schwimmschul-Allee to the northern entrance of the Rotunda, was
1528.3 meters; the gauge was 1 meter, and 60 per cent. of the length
consisted of tangents, the remaining 40 per cent. being mostly curves
of 250 meters radius. The gradients, three in number, were very small,
averaging about 1:750.
Two generating dynamos were used, which were coupled in parallel
circuit, but in such a manner that the difference of potential in both
machines remained the same at all times. This was accomplished by the
well known method of coupling introduced by Siemens and Halske, in which
the current of one machine excites the field of the other.
Although the railroad was not built with a view of obtaining a high
efficiency, an electro-motive force of only 150 volts being used, a
mechanical efficiency of 50 per cent. was nevertheless obtained, both
with one generator and one car with thirty passengers, as well as with
two generators and two cars with sixty passengers; while with two
generators and three cars (two of them having motors) the same result
was shown.
[Illustration: THE ELECTRIC RAILWAY AT VIENNA.]
The curves obtained by the apparatus that recorded the current showed
very plainly the action within the machines when the cars were started
or set in motion; at first, the current rose rapidly to a very high
figure, and then declined gradually to a fixed point, which corresponded
to the regular rate of speed. The tractive power, therefore, increases
rapidly to a value far exceeding the frictional resistances, but this
surplus energy serves to increase the velocity, and disappears as soon
as a uniform velocity is reached.
The average speed, both with one and three cars, was 30 kilometers per
hour.--_Zeitsch. f. Elektrotechnik_.
* * * * *
INSTRUCTION IN MECHANICAL ENGINEERING.
By Professor R. H. THURSTON.
The writer has often been asked by correspondents interested in
the matter of technical and trade education to outline a course of
instruction in mechanical engineering, such as would represent his
idea of a tolerably complete system of preparation for entrance into
practice. The synopsis given at the end of this article was prepared
in the spring of 1871, when the writer was on duty at the U.S. Naval
Academy, as Assistant Professor of Natural and Experimental Philosophy,
and, being printed, was submitted to nearly all of the then leading
mechanical engineers of the United States, for criticism, and with a
request that they would suggest such alterations and improvements as
might seem to them best. The result was general approval of the course,
substantially as here written. This outline was soon after proposed as a
basis for the course of instruction adopted at the Stevens Institute of
Technology, at Hoboken, to which institution the writer was at about
that time called. He takes pleasure in accepting a suggestion that its
publication in the SCIENTIFIC AMERICAN would be of some advantage to
many who are interested in the subject.
The course here sketched, as will be evident on examination, includes
not only the usual preparatory studies pursued in schools of mechanical
engineering, but also advanced courses, such as can only be taught in
special schools, and only there when an unusual amount of time can be
given to the professional branches, or when post graduate courses can be
given supplementary to the general course. The complete course, as here
planned, is not taught in any existing school, so far as the writer is
aware. In his own lecture room the principal subjects, and especially
those of the first part of the work, are presented with tolerable
thoroughness; but many of the less essential portions are necessarily
greatly abridged. As time can be found for the extension of the course,
and as students come forward better prepared for their work, the earlier
part of the subject is more and more completely developed, and the
advanced portions are taken up in greater and greater detail, each year
giving opportunity to advance beyond the limits set during the preceding
year.
Some parts of this scheme are evidently introductory to advanced courses
of study which are to be taken up by specialists, each one being adapted
to the special instruction of a class of students who, while pursuing
it, do not usually take up the other and parallel courses. Thus, a
course of instruction in Railroad Engineering, a course in Marine
Engineering, or a course of study in the engineering of textile
manufactures, may be arranged to follow the general course, and the
student will enter upon one or another of these advanced courses as his
talents, interests, or personal inclinations may dictate. At the Stevens
Institute of Technology, two such courses--Electrical and Marine
Engineering--are now organized as supplementary of the general course,
and are pursued by all students taking the degree of Mechanical
Engineer. These courses, as there given, however, are not fairly
representative of the idea of the writer, as above expressed, since the
time available in general course is far too limited to permit them to be
developed beyond the elements, or to be made, in the true sense of the
term, advanced professional courses. Such advanced courses as the writer
has proposed must be far more extended, and should occupy the whole
attention of the student for the time. Such courses should be given in
separate departments under the direction of a General Director of the
professional courses, who should be competent to determine the extent of
each, and to prevent the encroachment of the one upon another; but they
should each be under the immediate charge of a specialist capable
of giving instruction in the branch assigned to him, in both the
theoretical and purely scientific, and the practical and constructive
sides of the work. Every such school should be organized in such a
manner that one mind, familiar with the theory and the practice of the
professional branches taught, should be charged with the duty of giving
general direction to the policy of the institution and of directing
the several lines of work confided to specialists in the different
departments. It is only by careful and complete organization in this, as
in every business, that the best work can be done at least expense in
time and capital.
In this course of instruction in Mechanical Engineering it will be
observed that the writer has incorporated the scheme of a workshop
course. This is done, not at all with the idea that a school of
mechanical engineering is to be regarded as a "trade school," but that
every engineer should have some acquaintance with the tools and the
methods of work upon which the success of his own work is so largely
dependent. If the mechanical engineer can acquire such knowledge in the
more complete course of instruction of the trade school, either before
or after his attendance at the technical school, it will be greatly to
his advantage. The technical school has, however, a distinct field; and
its province is not to be confounded with that of the trade school.
The former is devoted to instruction in the theory and practice of a
profession which calls for service upon the men from the latter--which
makes demand upon a hundred trades--in the prosecution of its designs.
The latter teaches, simply, the practical methods of either of the
trades subsidiary to the several branches of engineering, with only so
much of science as is essential to the intelligent use of the tools and
the successful application of the methods of work of the trade taught.
The distinction between the two departments of education, both of which
are of comparatively modern date, is not always appreciated in the
United States, although always observed in those countries of Europe
in which technical and trade education have been longest pursued as
essential branches of popular instruction. Throughout France and
Germany, every large town has its trade schools, in which the trades
most generally pursued in the place are systematically taught; and every
large city has its technical school, in which the several professions
allied to engineering are studied with special development of those to
which the conditions prevailing at the place give most prominence and
local importance.
A course of trade instruction, as the writer would organize it, would
consist, first, in the teaching of the apprentice the use of the tools
of his trade, the nature of its materials, and the construction and
operation of the machinery employed in its prosecution. He would next be
taught how to shape the simpler geometrical forms in the materials of
his trade, getting out a straight prism, a cylinder, a pyramid, or a
sphere, of such size and form as may be convenient; getting lines and
planes at right angles, or working to miter; practicing the working of
his "job" to definite size, and to the forms given by drawings, which
drawings should be made by the apprentice himself. When he is able to
do good work of this kind, he should attempt larger work, and the
construction of parts of structures involving exact fitting and special
manipulations. The course, finally, should conclude with exercises in
the construction and erection of complete structures and in the making
of peculiar details, such as are regarded by the average workman
as remarkable "_tours de force_." The trade school usually gives
instruction in the common school branches of education, and especially
in drawing, free-hand and mechanical, carrying them as far as the
successful prosecution of the trade requires. The higher mathematics,
and advanced courses in physics and chemistry, always taught in schools
of engineering, are not taught in the trade school, as a rule; although
introduced into those larger schools of this class in which the aim is
to train managers and proprietors, as well as workmen. This is done in
many European schools.
As is seen above, the course of instruction in mechanical engineering
includes some trade education. The engineer is dependent upon the
machinist, the founder, the patternmaker, and other workers at the
trades, for the proper construction of the machinery and structures
designed by him. He is himself, in so far as he is an engineer, a
designer of constructions, not a constructor. He often combines,
however, the functions of the engineer, the builder, the manufacturer,
and the dealer, in his own person. No man can carry on, successfully,
any business in which he is not at home in every detail, and in which he
cannot instruct every subordinate, and cannot show every person employed
by him precisely what is wanted, and how the desired result can be best
attained. The engineer must, therefore, learn, as soon and as thoroughly
as possible, enough of the details of every art and trade, subsidiary
to his own department of engineering, to enable him to direct, with
intelligence and confidence, every operation that contributes to the
success of his work. The school of engineering should therefore be so
organized that the young engineer may be taught the elements of every
trade which is likely to find important application in his professional
work. It cannot be expected that time can be given him to make himself
an expert workman, or to acquire the special knowledge of details and
the thousand and one useful devices which are an important part of the
stock in trade of the skilled workman; but he may very quickly learn
enough to facilitate his own work greatly, and to enable him to learn
still more, with rapidity and ease, during his later professional life.
He must also, usually, learn the essential elements and principles of
each of several trades, and must study their relations to his work, and
the limitations of his methods of design and construction which they
always, to a greater or less extent, cause by their own practical or
economical limitations. He will find that his designs, his methods of
construction, and of fitting up and erecting, must always be planned
with an intelligent regard to the exigencies of the shop, as well as to
the aspect of the commercial side of every operation. This extension of
trade education for the engineer into several trades, instead of its
restriction to a single trade, as is the case in the regular trade
school, still further limits the range of his instruction in each. With
unusual talent for manipulation, he may acquire considerable knowledge
of all the subsidiary trades in a wonderfully short space of time, if he
is carefully handled by his instructors, who must evidently be experts,
each in his own trade. Even the average man who goes into such schools,
following his natural bent, may do well in the shop course, under good
arrangements as to time and character of instruction. If a man has not a
natural inclination for the business, and a natural aptitude for it, he
will make a great mistake if he goes into such a school with the hope of
doing creditable work, or of later attaining any desirable position in
the profession.
The course of instruction, at the Stevens Institute of Technology,
includes instruction in the trades to the extent above indicated. The
original plan, as given below, included such a course of trade education
for the engineer; but it was not at once introduced. The funds
available from an endowment fund crippled by the levying of an enormous
"succession tax" by the United States government and by the cost of
needed apparatus and of unanticipated expenses, in buildings and in
organization, were insufficient to permit the complete organization
of this department. A few tools were gathered together; but skilled
mechanics could not be employed to take up the work of instruction in
the several courses. Little could therefore be done for several years in
this direction. In 1875 the writer organized a "mechanical laboratory,"
with the purpose of attaining several very important objects: the
prosecution of scientific research in the various departments of
engineering work; the creation of an organization that should give
students an opportunity to learn the methods of research most usefully
employed in such investigations; the assistance of members of the
profession, and business organizations in the attempt to solve such
questions, involving scientific research, as are continually arising in
the course of business; the employment of students who had done
good work in their college course, when they so desire, in work of
investigation with a view to giving them such knowledge of this peculiar
line of work as should make them capable of directing such operations
elsewhere; and finally, but not least important of all, to secure, by
earning money in commercial work of this kind, the funds needed to carry
on those departments of the course in engineering that had been, up
to that time, less thoroughly organized than seemed desirable. This
"laboratory" was organized in 1875, the funds needed being obtained
by drawing upon loans offered by friends of the movement and by the
"Director."
It was not until the year 1878, therefore, that it became possible to
attempt the organization of the shop course; and it was then only by the
writer assuming personal responsibility for its expenses that the plan
could be entered upon. As then organized--in the autumn of 1878--a
superintendent of the workshop had general direction of the trade
department of the school. He was instructed to submit to the writer
plans, in detail, for a regular course of shop instruction, and was
given as assistants a skilled mechanic of unusual experience and
ability, whose compensation was paid from the mechanical laboratory
funds, and guaranteed by the writer personally, and another aid whose
services were paid for partly by the Institute and partly as above. The
pay of the superintendent was similarly assured. This scheme had been
barely entered upon when the illness of the writer compelled him to
temporarily give up his work, and the direction of the new organization
fell into other hands, although the department was carried on, as above,
for a year or more after this event occurred.
The plan did not fall through; the course of instruction was
incorporated into the college course, and its success was finally
assured by the growth of the school and a corresponding growth of its
income, and, especially, by the liberality of President Morton, who met
expenses to the amount of many thousands of dollars by drawing upon his
own bank account. The department was by him completely organized, with
an energetic head, and needed support was given in funds and by a force
of skilled instructors. This school is now in successful operation.
This course now also includes the systematic instruction of students in
experimental work, and the objects sought by the writer in the creation
of a "mechanical laboratory" are thus more fully attained than they
could have possibly been otherwise. It is to be hoped that, at
some future time, when the splendid bequest of Mr. Stevens may be
supplemented by gifts from other equally philanthropic and intelligent
friends of technical education, among the alumni of the school and
others, this germ of a trade school maybe developed into a complete
institution for instruction in the arts and trades of engineering, and
may thus be rendered vastly more useful by meeting the great want, in
this locality, of a real trade school, as well as fill the requirements
of the establishment of which it forms a part, by giving such trade
education as the engineer needs and can get time to acquire.
The establishment of advanced courses of special instruction in
the principal branches of mechanical engineering may, if properly
"dovetailed" into the organization, be made a means of somewhat
relieving the pressure that must be expected to be felt in the attempt
to carry out such a course as is outlined below. The post-graduate
or other special departments of instruction, in which, for example,
railroad engineering, marine engineering, and the engineering of cotton,
woolen, or silk manufactures, are to be taught, may be so organized that
some of the lectures of the general course may be transferred to them,
and the instructors in the latter course thus relieved, while the
subjects so taught, being treated by specialists, may be developed more
efficiently and more economically.
Outlines of these advanced courses, as well as of the courses in trade
instruction comprehended in the full scheme of mechanical engineering
courses laid out by the writer a dozen years ago, and as since recast,
might be here given, but their presentation would occupy too much space,
and they are for the present omitted.
The course of instruction in this branch of engineering, at the Stevens
Institute of Technology, is supplemented by "Inspection Tours," which
are undertaken by the graduating class toward the close of the last
year, under the guidance of their instructors, in which expeditions they
make the round of the leading shops in the country, within a radius of
several hundred miles, often, and thus get an idea of what is meant by
real business, and obtain some notion of the extent of the field of work
into which they are about to enter, as well as of the importance of
that work and the standing of their profession among the others of the
learned professions with which that of engineering has now come to be
classed.
At the close of the course of instruction, as originally proposed, and
as now carried out, the student prepares a "graduating thesis," in which
he is expected to show good evidence that he has profited well by the
opportunities which have been given him to secure a good professional
education. These theses are papers of, usually, considerable extent, and
are written upon subjects chosen by the student himself, either with or
without consultation with the instructor. The most valuable of
these productions are those which present the results of original
investigations of problems arising in practice or scientific research
in lines bearing upon the work of the engineer. In many cases, the
work thus done has been found to be of very great value, supplying
information greatly needed in certain departments, and which had
previously been entirely wanting, or only partially and unsatisfactorily
given by authorities. Other theses of great value present a systematic
outline of existing knowledge of some subject which had never before
been brought into useful form, or made in any way accessible to the
practitioner. In nearly all cases, the student is led to make the
investigation by the bent of his own mind, or by the desire to do work
that may be of service to him in the practice of his profession. All
theses are expected to be made complete and satisfactory to the head
of department of Engineering before his signature is appended to the
diploma which is finally issued to the graduating student. These
preliminaries being completed, and the examinations having been reported
as in all respects satisfactory, the degree of Mechanical Engineer is
conferred upon the aspirant, and he is thus formally inducted into the
ranks of the profession.
COURSE OF INSTRUCTION IN MECHANICAL ENGINEERING.
Robert H. Thurston--July, 1871.
I.
MATERIALS USED IN ENGINEERING.--Classification, Origin, and Preparation
(where not given in course of Technical Chemistry), Uses, Cost.
_Strength and Elasticity_.--Theory (with experimental illustrations),
reviewed, and tensile, transverse and torsional resistance determined.
_Forms_ of greatest strength determined. _Testing_ materials.
_Applications_.--Foundations, Framing in wood and metal.
FRICTION.--Discussion from Rational Mechanics, reviewed and extended.
_Lubricants_ treated with materials above.
Experimental determination of "coefficients of friction."
II.
TOOLS.--Forms for working wood and metals. Principles involved in their
use.
Principles of pattern making, moulding, smith and machinists' work so
far as they modify design.
Exercises in Workshops in mechanical manipulation.
Estimates of _cost_ (stock and labor).
MACHINERY AND MILL WORK.--Theory of machines. Construction. Kinematics
applied. Stresses, calculated and traced. Work of machines. Selection
of materials for the several parts. Determination of _proportions_ of
details, and of _forms_ as modified by difficulties of construction.
Regulators, Dynamometers, Pneumatic and Hydraulic machinery. Determining
_moduli_ of machines.
POWER, transmission by gearing, belting, water, compressed air, etc.
LOADS, transportation.
III.
HISTORY AND PRESENT FORMS OF THE PRIME MOVERS.
_Windmills_, their theory, construction, and application.
_Water Wheels_. Theory, construction, application, testing, and
comparison of principal types.
_Air, Gas, and Electric Engines_, similarly treated.
STEAM ENGINES.--Classification. [Marine (merchant) Engine assumed as
representative type.] Theory. Construction, including general design,
form and proportion of details.
_Boilers_ similarly considered. Estimates of _cost_.
_Comparison_ of principal types of Engines and Boilers. Management and
repairing. Testing and recording performance.
IV.
MOTORS APPLIED to Mills. Estimation of required power and of _cost_.
Railroads. Study of Railroad machinery.
Ships. Structure of Iron Ships and rudiments of Naval architecture and
Ship propulsion.
PLANNING Machine shops, Boiler shops, Foundries, and manufactories of
textile fabrics. Estimating _cost_.
LECTURES BY EXPERTS.
GENERAL SUMMARY of principal facts, and natural laws, upon the thorough
knowledge of which successful practice is based; and general _resume_
of principles of business which must be familiar to the practicing
engineer.
V.
GRADUATING THESES.
GRADUATION.
Accompanying the above are courses of instruction in higher mathematics,
graphics, physics, chemistry, and the modern languages and literatures.
* * * * *
IMPROVED DOUBLE BOILER.
The operation of boiling substances under pressure with more or less
dilute sulphuric or sulphurous acid forms a necessary stage of several
important manufactures, such as the production of paper from wood, the
extraction of sugar, etc. A serious difficulty attending this process
arises from the destructive action of the acid upon the boiler or
chamber in which the operation is carried on, and as this vessel, which
is generally of large dimensions, is exposed to considerable pressures,
it is necessarily constructed of iron or some other sufficiently
resisting metal. An ingenious method of avoiding this difficulty has
been devised, we believe in Germany, and has been put into practice with
a certain amount of success. It consists in lining the iron boiler with
a covering of lead, caused by fusion to unite firmly to the walls of the
boiler, and thus to protect it from the action of the acid. No trouble,
it is stated, is found to arise from the difference in expansion of the
two metals, which, moreover, adhere fairly well; but, on the other hand,
we believe it does actually occur that the repairs to this lead lining
are numerous, tedious, and costly of execution, so that the system can
scarcely be regarded as meeting the requirements of the manufacturer.
It is to secure all the advantages possessed by a lead-lined vessel,
without the drawback of frequent and expensive repairs, that the
digester, of which we annex illustrations, has been devised by Mr.
George Knowles, of Billiter House, Billiter Street. It consists of a
closed iron cylindrical vessel suitable for boiling under pressure, and
containing a second vessel open at the top, and of such a diameter as to
leave an annular space between it and the walls of the outer shell. This
inner receiver, which may be made of lead, glass, pottery, or any
other suitable material, contains the substance to be treated and the
sulphurous acid or other solution in which it is to be boiled. The
annular space between the two vessels is filled with water to the same
level as the solution in the receiver, and the latter is provided with
suitable pipes or coils, in which steam is caused to circulate for
the purpose of raising the solution of the desired temperature, and
effecting the digesting process. At the same time any steam generated
collects in the upper part of the boiler, and maintains an equal
pressure within the whole apparatus. Figs. 1 to 3 show the arrangement
clearly. Within the boiler, a, is placed the receiver, b, of pottery,
lead, or other material, leaving an annular space between it and the
boiler; this space is filled with water. The receiver, b, is furnished
with a series of pipes, in which steam or hot water circulates, to heat
the charge to the desired temperature. These pipes may be arranged
either in coils, as shown at d, Fig. 1, or vertically at d, Fig. 3. The
latter are provided with inner return pipes, so that any condensed water
accumulating at the bottom may be forced up the inner pipes by the
steam pressure and escape at the top. The vessel is charged through the
manhole, e, and the hopper, c, provided with a perforated cover, and is
discharged at the bottom by the valve, f, shown in Figs. 2 and 3. The
upper part of the boiler serves as a steam dome, and the pressure on the
liquid in the receiver and on the water in the annular space is thereby
maintained uniform. The necessary fittings for showing the pressure
in the vessel, water level indicator, safety valve, cocks for testing
solutions, etc., are of course added to the apparatus, but are not
indicated in the drawing. The arrangement appears to us to possess
considerable merit, and we shall refer to it again on another occasion,
after experiments have been made to test its efficiency.--_Engineering_.
[Illustration: IMPROVED DOUBLE BOILER.]
* * * * *
THE GARDNER MACHINE GUN.
[Illustration: FIG. 1.--SINGLE BARREL GARDNER MACHINE GUN.]
The mechanism by which the various functions of loading, firing, and
extracting are performed is contained in a rectangular gun metal case,
varying in dimensions with the number of barrels in the arm. In the
single barrel gun the size of this case is 14 inches in length, 51/2
inches in depth, and 21/2 inches in width. The top of the box is hinged,
so that easy access can be had to the mechanism, which consists of a
lock, the cartridge carrier, and the devices for actuating them. In the
multiple barrel guns, the frames which, with the transverse bar at the
end, hold the barrels in place, form the sides of the mechanism chamber,
in the front end of which the barrels are screwed. The mechanism is
actuated by a cam shaft worked by a hand crank on one side of the
chamber. By this means the locks are driven backward and forward,
the latter motion forcing the cartridges into place, and the former
withdrawing the empty cartridge case after firing. The extractor hook
pivoted to the lock plunger rises, as the lock advances, over the rim of
the case, but is rigid as the lock is withdrawn, so that the action is
a positive one. The cartridges, which are contained in a suitable
frame attached to the forward part of the breech chamber, pass through
openings in the top plate of the latter, an efficient distribution being
secured by means of a valve having a transverse motion. Each cartridge
as it falls is brought into the axis of the barrel and the plunger,
while the advance motion of the lock forces them into position. In the
five-barrel gun illustrated by Fig. 3 the cartridge feeder contains 100
cartridges, in five Vertical rows of 20 cartridges each, and these are
kept supplied, when firing, from supplementary holders. Fig. 1 shows the
portable rest manufactured by the Gardner Gun Company. It consists of
two wrought iron tubes, placed at right angles to each other; the front
bar can be easily unlocked, and placed in line with the trail bar, from
which project two arms, each provided with a screw that serves for the
lateral adjustment of the gun. These screws are so arranged as to allow
for an oscillating motion of the gun through any distance up to 15 deg.
The tripod mounting, used for naval as well as land purposes, is shown
in Fig. 2, which illustrates the two barrel gun complete. The five
barrel gun, Fig. 3, is shown mounted on a similar tripod. The length of
this weapon over all is 53.5 inches, the barrels (Henry system) are 33
inches long, with seven grooves of a uniform twist of one turn in 22
inches.
[Illustration: Fig. 2.--TWO BARREL GARDNER GUN.]
Gardener's five barrel gun in the course of one of the trials fired
16,754 rounds with only 24 jams, and in rapid firing reached a maximum
of 330 shots in 30 seconds. The two barrel gun fired 6,929 rounds
without any jam; the last 3,000 being in 11 minutes 39 seconds, without
any cleaning or oiling.--_Engineering_.
[Illustration: Fig. 3.--FIVE BARREL GARDNER GUN.]
* * * * *
CLIMBING TRICYCLES.
The cycle trade is one which has been developed with great rapidity
within the last ten years, and, like all new industries, has called
forth a considerable amount of ingenuity and skill on the part of those
engaged in it. We cannot help thinking, however, that much of this
ingenuity has been misplaced, and that instead of striving after new
forms involving considerable complication and weight, it would have
been better and more profitable if manufacturers had moderated their
aspirations, and aimed at greater simplicity of design; for it must
be remembered that cyclists are, as a rule, without the slightest
mechanical knowledge, while the machines themselves are subject to very
hard usage and considerable wear and tear in traveling over the
ordinary roads in this country. We refer, of course, more especially to
tricycles, which in one form or another are fast taking the place of
bicycles, and which promise to assume an important position in every
day locomotion. Hitherto one of the chief objections to the use of the
tricycle has been the great difficulty experienced in climbing hills, a
very slight ascent being sufficient to tax the powers of the rider to
such an extent as to induce if not compel him in most instances to
dismount and wheel his machine along by hand until more favorable ground
is reached. To obviate this inconvenience many makers have introduced
some arrangement of gearing speeds of two powers giving the necessary
variation for traveling up hill and on the level. We noticed, however,
one machine at the exhibition which seemed to give all that could be
desired without any gearing or chains at all. This was a direct action
tricycle shown by the National Cycle Company, of Coventry, in which the
pressure from the foot is made to bear directly upon the main axle, and
so transmitted without loss to the driving wheels on each side, the
position of the rider being arranged so that just sufficient load is
allowed to fall on the back wheel as to obtain certainty in steerage.
The weight of this machine is much less than when gearing is used, and
the friction is also considerably reduced, trials with the dynamometer
having shown that on a level, smooth road, a pull of 1 lb. readily
moved it, while with a rider in the seat 4 lb. was sufficient. On this
tricycle any ordinary hill can, it is stated, be ascended with great
ease, and as a proof of its power it was exhibited at the Stanley show
climbing over a piece of wood 8 in. high, without any momentum whatever.
We understand that at the works at Coventry a flight of stairs has been
erected, and that no difficulty is experienced in ascending them on one
of these machines.--_The Engineer_.
* * * * *
SUBMARINE EXPLORATIONS.
VOYAGE OF THE TALISMAN.
It was but a few years ago that the idea was prevalent that the seas at
great depths were immense solitudes where life exhibited itself under no
form, and where an eternal night reigned. To-day, thanks to expeditions
undertaken for the purpose of exploring the abysses of the ocean, we
know that life manifests itself abundantly over the bottom, and that
at a depth of five and six thousand meters light is distributed by
innumerable phosphorescent animals. Different nations have endeavored to
rival each other in the effort to effect these important discoveries,
and several scientific missions have been sent to different points of
the globe by the English and American governments. The French likewise
have entered with enthusiasm upon this new line of research, and for
four consecutive years, thanks to the devoted aid of the ministry of the
marine, savants have been enabled to take passage in government vessels
that were especially arranged for making submarine explorations.
[Illustration: THE FRENCH SCIENTIFIC STEAMER TALISMAN.]
The first French exploration, which was an experimental trip, was made
in 1880 by the Travailleur in the Gulf of Gascogne. Its unhoped
for results had so great an importance that the following year the
government decided to continue its researches, and the Travailleur was
again put at the disposal of Mr. Alph. Milne Edwards and the commission
over which he presided. Mr. Edwards traversed the Gulf of Gascogne,
visited the coast of Portugal, crossed the Strait of Gibraltar, and
explored a great portion of the Mediterranean. In 1882 the same vessel
undertook a third mission to the Atlantic Ocean, and as far as to the
Canary Islands. The Travailleur, however, being a side-wheel advice-boat
designed for doing service at the port of Rochefort, presented none
of those qualities that are requisite for performing voyages that are
necessarily of long duration. The quantity of coal that could be stored
away in her bunkers was consumed in a week, and, after that, she could
not sail far from the points where it was possible for her to coal up
again. So after her return Mr. Edwards made a request for a ship that
was larger, a good sailer, and that was capable of carrying with it a
sufficient supply of fuel for remaining a long time at sea, and that
was adapted to submarine researches. The Commission indorsed this
application, and the Minister of Instruction received it and transmitted
it to Admiral Jaureguiberry--the Minister of the Marine--who at once
gave orders that the Talisman should be fitted up and put in commission
for the new dredging expedition. This vessel, under command of Captain
Parfait, who the preceding year had occupied the same position on the
Travailleur, left the port of Rochefort on the 1st of June, 1883, having
on board Mr. Milne Edwards and the scientific commission that had been
appointed by the Minister of Public Instruction. The Talisman explored
the coasts of Portugal and Morocco, visited the Canary and Cape Verd
Islands, traversed the Sea of Sargasso, and, after a stay of some time
at the Azores, returned to France, after exploring on its way the Gulf
of Gascogne (Fig.).
[Illustration: FIG.1.--CHART OF THE TALISMAN'S VOYAGE.]
The magnificent collections in natural history that were collected
on this cruise, and during those of preceding years made by the
Travailleur, are, in a few days, to be exhibited at the Museum of
Natural History. We think we shall be doing a service to the readers of
this journal, in giving them some details as to the organization of the
Talisman expedition as well as to the manner in which the dredgings were
performed.
[Illustration: FIG.2.--PLAN OF THE VESSEL.]
The vessel, as shown by her plan in Fig. 2, had to undergo important
alterations for the cruise that she was to undertake. Her deck was
almost completely freed from artillery, since this would have encumbered
her too much. Immediately behind the bridge, in the center of the
vessel, there were placed two windlasses, one, A, to the right, and the
other, B, to the left (Fig. 2). These machines, whose mode of operation
will be explained further along, were to serve for raising and lowering
the fishing apparatus. A little further back there were constructed
two cabins, G and HH. The first of these was designed to serve as a
laboratory, and the second was arranged as quarters for the members of
the mission.
The sounding apparatus, the Brothergood engine for actuating it, and the
electric light apparatus were placed upon the bridge. The operating
of the sounding line and of the electric light was therefore entirely
independent of that of the dredges. On the foremast, at a height of
about two meters, there was placed a crane, F, which was capable of
moving according to a horizontal plane. Its apex, as may be seen from
the plan of the boat, was capable of projecting beyond the sides of the
ship, to the left and right. To this apex was fixed a pulley over which
ran the cable that supported the dredges or bag-nets, which latter were
thus carried over the boat's sides.
[Illustration: FIG.3.--DIAGRAM OF THE THIBAUDIER SOUNDING APPARATUS.]
The preliminary operation in every submarine exploration consists in
exactly determining the depth of the sea immediately beneath the vessel.
To effect this object different sounding apparatus have been proposed.
As the trials that were made of these had shown that each of them
possessed quite grave defects, Mr. Thibaudier, an engineer of the navy,
installed on board the Talisman last year a new sounding apparatus which
had been constructed according to directions of his and which have given
results that are marvelous. The apparatus automatically registers the
number of meters of wire that is paid out, and as soon as the sounding
lead touches bottom, it at once stops of itself. This apparatus is shown
in Fig. 4, and a diagram of it is given in Fig. 3, so that its operation
may be better understood. The Thibaudier sounding apparatus consists of
a pulley, P (Fig. 3), over which is wound 10,000 meters of steel wire
one millimeter in diameter. From this pulley, the wire runs over a
pulley, B, exactly one meter in circumference; from thence it runs to a
carriage, A, which is movable along wooden shears, runs up over a fixed
pulley, K, and reaches the sounding lead, S, after traversing a guide,
g, where there is a small sheave upon which it can bear, whatever be the
inclination of the boat. The wheel, B, carries upon its axle an endless
screw that sets in motion two toothed wheels that indicate the number
of revolutions that it is making. One of these marks the units and the
other the hundredths (Fig. 5). This last is graduated up to 10,000
meters. As every revolution of the wheel, B, corresponds to one meter,
the number indicated by the counter represents the depth. Upon the axle
of the winding pulley there is a break pulley, p. The brake, f, is
maneuvered by a lever, L, at whose extremity there is a cord, C, which
is made fast to the carriage, A. When, during the motions due to
rolling, the tension of the steel wire that supports the lead diminishes
or increases, the carriage slightly rises or falls, and, during these
motions, acts more or less upon the brake and consequently regulates the
velocity with which the wire unwinds. When the lead touches bottom, the
wire, being suddenly relieved from all weight (which is sometimes as
much as 70 kilos), instantly stops.
[Illustration: FIG. 4.--GENERAL VIEW OF THE SOUNDING APPARATUS IN THE
"TALISMAN:"]
The maneuver of this apparatus may be readily understood. The apparatus
and its weights are arranged in the interior of the vessel. A man bears
upon the lever, L (Fig. 3), and the counter is set at zero. All being
thus arranged, the man lets go of the break, and the unwinding then
proceeds until the lead has touched bottom. During the operation of
sounding, the boat is kept immovable by means of its engine, so that the
wire shall remain as vertical as possible. The bottom being reached, the
unwinding suddenly ceases, and there is nothing further to do but read
the indication given by the differential counter, this giving the depth.
[Illustration: FIG. 5.--APPARATUS FOR MEASURING THE LENGTH OF THE WIRE
PAID OUT.]
Near the winding pulley, there is a small auxiliary engine, M, which
is then geared with the axle of the said pulley, and which raises the
sounding apparatus that has been freed from its weight by a method that
will be described further along.
We have endeavored in Fig. 4 to show the aspect of the bridge at the
moment when a sounding was about being made. From this engraving (made
from a photograph) our readers may obtain a clear idea of the Thibaudier
sounding apparatus, and understand how the wheel over which the wire
runs is set in motion by the Brothergood engine.--_La Nature_.
* * * * *
CABLE GRAPNEL.
Some improvements have recently been made by Mr. Alexander Glegg and the
inventor in the well-known Jamieson grapnel used for raising submerged
submarine cables. The chief feature of the grapnel is that the flukes,
being jointed at the socket, bend back against a spring when they catch
a rock, until the grapnel clears the obstruction, but allow the cable
to run home to the crutch between the fluke and base, as shown in the
figures. In the older form the cable was liable to get jammed, and cut
between the fixed toe or fluke and the longer fluke jointed into it.
This is now avoided by embracing the short fluke within the longer one.
The shank, formerly screwed into the boss, is now pushed through and
kept up against the collar of the boss, by the volute spring, which at
the same time presses back the hinged flukes after being displaced by
a rock. The shank can now freely swivel round, whereas before it was
rigidly fixed. The toes or flukes are now made of soft cast steel, which
can be straightened if bent, and the boss is made of cast steel or
gun-metal.
[Illustration: JAMIESON'S GRAPNEL.]
* * * * *
WRETCHED BOILERMAKING.
_To the Editor of the Scientific American_:
As long as I have been a reader of the SCIENTIFIC AMERICAN I have been
pleased with the manner in which you investigate and explain the cause
of any boiler explosion which comes to your knowledge; and I have
rejoiced when you heaped merited censure upon the fraudulent
boilermaker. In your paper in December last you copied a short article
on "Conscience in Boilermaking," in which the writer, after speaking
of the tricks of the boilermaker in using thinner iron for the center
sheets than for the others, and in "upsetting" the edges of the plates
to make them appear thicker, goes on to say: "We call attention to this,
because the discovery of such practice has made serious trouble between
the boilermaker and the steam user. We would not believe that there were
men so blind to the duties and obligations which rest upon them as
to resort to such practice, but the careful inspector finds all such
defects, and in time we come to know whose work is carefully and
honestly done, and whose is open to suspicion. In States and cities
where inspection laws are in force that give the methods and rules by
which the safe working pressure of a boiler is calculated, there is no
alternative except to follow the rules; and if certain requirements
regarding construction are a part of the law, there is no authority or
right to depart from it, and yet there are boilermakers who try to force
their boilers into such localities when their work is not up to the
requirements of the law."
Now, if some boilermakers are so dishonest as to try and impose upon the
locomotive engineer, who they know will carefully examine every part of
his boiler, and who is able to detect any flaw, it is not to be expected
that the farmer will escape. Nor does he. The great number of explosions
of boilers used in thrashing and in other farm work proves that there
are boilermakers who "force their boilers into such localities
when their work is not up to the requirements of the law." And the
boilermaker, if he be dishonest, is doubly tempted if the broad width of
a continent intervenes between him and the farmer for whom his work is
intended, and if in the place where the boiler is to be used there are
no inspection laws in force. The farmer who lives many miles from a
city, and who has no means of testing any boiler he may purchase,
is wholly at the mercy of the boilermaker, and must run it until it
explodes or time proves it to have been honestly made. Then, again,
there are boilermakers who, although making boilers of good iron and of
the proper thickness, finish them off so badly that the farmer is put to
great inconvenience and expense to put them in working order. Two years
ago I purchased a straw-burning engine and boiler made by an Eastern
firm. Before it had run ten days the boiler began to leak at the
saddle-bolt holes. The engineer tightened the nuts as far as possible,
but could not stop the leaks, which at last became so bad that we had to
stop work and take the engine to the shop. Upon taking off the saddle
and taking out the bolts it was discovered that they were too small for
the holes in the boiler, and that they had been wrapped with candle wick
and white lead to make them fill the holes, and that a light washer had
been put on each bolt between the head and the inside of the boiler.
This washer kept the lead in its place, and prevented the boiler from
showing a leak when first fired up. The water pipes in the fire-box soon
gave out and became utterly useless. Upon inquiring of the patentee of
this straw-burning device, who was supposed to have put it in my boiler,
he stated that he had had nothing to do with it, but that it was put in
by the firm selling these engines, and "as cheaply as possible." Before
I got this boiler and engine in fair running order I had spent hundreds
of dollars and had to do entirely away with the water grates.
Last summer, needing another tharshing engine, I was induced to buy
one of the same make as my old one, but with a different straw-burning
device. The firm who sold it to me agreed that it should have none of
the faults of the old one. Well, I got it, and, upon hauling it out to
my ranch, and getting up steam, I found it to be much worse than the
first one I had bought. The boiler leaked at nearly every hole where
a tap had been screwed into it. It took an engineer, a boilermaker, a
blacksmith, and a fireman several days to get it in shape so that we
could use it at all; and after we did start up, the boilermaker had
to be sent for several times to stop new leaks that were continually
showing themselves.
I send you by this mail for your inspection one of the saddle bolts and
one of the bolts taken out of the piston, and also the certificates of
the engineer, boilermaker, and machinist who repaired the boiler. In
justice to my fellow-farmers I ought to publish these certificates and
the names of these boilermakers to the world, but, for the present at
least, I refrain from so doing. These boilermakers will see this article
and they will know, if the public does not, for whom it is intended. If
it has the effect of making them exercise more care in the construction
and fitting up of their engines and boilers, I have not written in vain.
D. FREEMAN.
Los Angeles, Cal., March 7,1884.
[The two bolts and the certificates above referred to accompany the
letter of Mr. Freeman. We can only wonder how it was that, after having
been treated as he relates in the first instance, he should have had any
further business with parties who would send out such boilers, for the
testimony of the engineer and workmen make the case even stronger than
Mr. Freeman has put it.--ED.]
* * * * *
A THREADED SET COLLAR.
There are cases where a long screw must be rotated with a traversing nut
or other threaded piece traveling on its thread a limited and variable
distance. At one time the threaded nut or piece may be required to
go almost the entire length of the screw, and at another time a much
shorter traverse would be required. In many instances the use of side
check nuts is inconvenient, and in some it is impossible. One way of
utilizing the nut as a set collar is to drill through its side for a set
screw, place it on its screw, pour a little melted Babbitt metal, or
drop a short, cold plug of it into the hole, tap the hole, and the tap
will force the Babbitt into the threads.
Insert the set screw, and when it acts on the Babbitt metal it will
force it with great friction on to the thread without injuring the
thread; and when the set screw tension is released, the nut turns
freely. A similar and perhaps a better result may be obtained by
slotting the hole through the nut as though for the reception of a key.
Secure a key (preferably of the same material as the nut) by slight
upsetting at its ends, and then thread the nut, key, and all. Place
a set screw through the nut over the threaded key, and the job is
complete.
* * * * *
PNEUMATIC MALTING.
The lethargy in the malting trade, and in all matters relating to
malting processes, induced by two centuries of restrictive legislation,
is being gradually shaken off by the malting industry under the new law.
For many years nearly all improvements in malting processes originated
abroad, as numberless Acts of Parliament fettered every process and the
use of every implement requisite in a malt-house in this country. The
entire removal of these legislative restrictions gives an opportunity
for improved processes, which promises to open up a considerable
field for engineering work, and to develop a very backward art by the
application of scientific principles. The present time is, therefore,
one of more material change than malting has ever experienced.
[Illustration: PNEUMATIC MALTING AT TROYES. Fig. 1.]
Of the numerous improvements effected in the past few years, those made
by M. Galland in France, and more recently by M. Saladin, are by far the
most prominent. M. Galland originated what is known as the pneumatic
system eight or nine years ago. This system is carried out at the
Maxeville brewery, near Nancy.
[Illustration: PNEUMATIC MALTING AT TROYES. Fig. 2.]
Since that time further improvements have been made by M. Galland; but
more recently great advances have been made in the system by M.
Saladin. He has developed the practice of the leading principle, and in
conjunction with Mr. H. Stopes, of London, has added improved kilns and
various mechanical apparatus for performing the work previously done by
hand. He has also devised a very ingenious machine for cooling the moist
air by which the process is carried on.
[Illustration: FIG. 4.--ECHANGEUR AND TURNING MACHINE.]
At the recent Brewery Exhibition, some of the machinery used in these
new maltings was shown in action by Messrs. H. Stopes & Co., together
with drawings of a malting constructed at Troyes for M. Bonnette under
M. Saladin's instructions. This malting is the third constructed for the
same firm, the others being at Nancy. That at Troyes we now illustrate.
We will not occupy space by a general description of the pneumatic
system, one great feature in which is the continuous manufacture of malt
throughout the year instead of only from five to eight months of the
year, as it will be gathered from the following description of the
Troyes malting:
[Illustration: FIG. 5.--ECHANGEUR, AXIAL SECTION.]
In our engravings, Figs. 1, 2, and 3, the letter A indicates the
germinating cases; B, Saladin's patent turning screws; C A, air
channels; D, passages; E R, main driving shafts; e, pulleys; F, metal
recesses to fit turning screws; G, elevators; H, trap doors; I, air
channels; J, openings to growing floor for air; K S, engines and fan
room; L N, fans, supply and exhaust; T, boiler; U, chimney; f, well. The
capacity of the malting is 130 qr. malt every day. This is equivalent to
an English house of 520 qr. steep. The whole space occupied is the area
necessary for kilns, malt and barley stores, engine and boiler house,
and fans. No additional area is required for germinating floors, as ten
germinating cases, A, are placed in the basement below the kilns and
stores. The building is of brick, with the internal walls below the
ground line resting upon cast iron columns and rolled joists. The
germinating cases, A A, are of iron; the bottoms are double. One of
perforated plate is placed 6 inches above the bottom. These plates admit
of draining the corn if the germinating case is used as a steeping
cistern also. Their chief object is, however to admit of ready
circulation of the air by the means presently to be described. Large
channels, A a, serve as drains for moisture and to convey the air to or
from the growing corn. Between each case is a passage, D, enabling the
maltster to have free access to the corn at all points.
[Illustration: FIG. 6.--ECHANGEUR TRANSVERSE SECTION.]
With the exception of the driving shaft, E, all the machinery is in
duplicate, so that the possibility is remote of any breakdown that would
seriously affect the working of the house. This is necessary, as should
the fans, L N, be stopped for twenty-four hours the corn germinating
at a depth exceeding 30 inches would heat and impair its vitality. The
boilers, T, and engines, S, are of the common type of 20 horse power
nominal. The fans, L N, are the Farcot patent, illustrated a short time
since in our pages. The lower floors of the kilns are provided with
the Schlemmer patent mechanical turners. The turners, Fig. 4, in the
germinating cases are Saladin's patent.
[Illustration: FIG. 7.--ECHANGEUR, SECTIONAL PLAN.]
The germination of the grain is effected by means of cool moist air
provided by the fan described and the cooler and moistener--Figs. 5, 6,
and 7, herewith--known as an _echangeur_. As the germinating grain has
a depth of from 30 inches to 40 inches some pressure is required, and
mechanical means are necessary for efficient and economical turning.
The _echangeur_ is a very ingenious application of the well understood
rapidity of evaporation of any liquid when spread out in very thin
layers over large surfaces and exposed to a current of air. It consists
of a cylinder, or series of cylinders, of increasing diameter, placed
one within another. Each consists of finely perforated sheet iron. They
are placed in a trough of water, just sufficiently immersed to insure
complete wetting. When rotated at a slow speed, the surfaces of all the
cylinders are kept just wetted. A volume of air is either driven or
drawn through, as may be required for any particular purpose. In the
model malting, as shown at Fig. 4, taken from that shown at the Brewery
Exhibition, the air was driven through the _echangeur_ and thence
through the germinating barley. Here or as employed in the malting
illustrated, the air in its passage comes first into contact with the
moistened cylinders, and if hot and dry it becomes moist and cool, for
the constant evaporation upon the cylinders has a very considerable
refrigerating effect.
This was well known to the Egyptians over four thousand years ago, and
the porous bottle--_gergeleh_--of Esnch has been made until the present
day, to keep the drinking water cool and fresh. The _echangeur_ is
like a gigantic gergeleh, and by increasing the size and number of the
cylinders, and causing the water in the moistening trough to circulate,
any volume of air can be wetted to the saturation limit corresponding to
its temperature. It will be seen that this apparatus gives the maltster
complete control of the humidity and heat as well as volume of the air
driven through germinating corn.
[Illustration: Fig. 8.]
The turning apparatus is shown by Fig. 4, and consists, as will be seen,
of a cylindrical frame provided with rollers which run on rails at the
edge of the germinating cases. It is carried to and fro from either end
of the case by compensating rope gearing which at the same time gives
motion to the gearing actuating the turning screws. These screws do not
quite touch the bottom of the germinating case, but are provided with a
pair of small brushes, as shown in the annexed engraving, Fig. 8, which
just skim it. The apparatus shown has but three of these screws, but the
cases are generally made wide enough for six. The kilns are double,
each possessing two floors, and worked upon the Stopes' system. The
construction of the furnaces is of the ordinary French pattern. The
arrangement of the house permits of great regularity in working. Every
day 130 qrs. of barley is screened, sorted, cleaned, and passed into a
steeping cistern. When sufficiently steeped it runs through piping into
the germinating case, which, in the natural order of working, is empty.
Here it forms the couch. When it is desirable to open couch a small
amount of air is forced through the grain by opening the trap door
connected with the main air channel. This furnishes the growing corn
with oxygen, removes the carbonic acid gas, and regulates temperatures
of the mass of grain. Later the Saladin turner is put in motion about
every eight to twelve hours. The screws in rotating upon their axes are
slowly propelled horizontally. They thus effectually turn the grain and
leave it perfectly smooth. This turning prevents matting of the roots,
the regulation of temperature and exposure to air being effected
by means of the cold air from the _echangeur_. When the grain is
sufficiently grown it is elevated to the kilns. For forty hours it
remains upon the top floor. It is then dropped upon the bottom floor, a
further charge of green corn following upon the top floor. The benefit
is mutual. The bottom floor is maintained at an even temperature, being
virtually plunged in an air bath; free radiation of heat is prevented;
the top surface of the malt is necessarily nearly as warm as that next
the wires, which in its turn is subject to lower heats than would be
necessary if free radiation from the surface was allowed. The top floor
is by the intervention of the layer of malt between it and the fire
prevented it from coming into direct contact with heat of a dangerous
and damaging degree. The same heat which is used to dry one floor, and
in an ordinary kiln passes at once into the air as waste, is the best
possible description of heat, namely, very slightly moistened heated
air, to remove the moisture from the second layer of malt at a low
temperature. It is of vital importance to retain this green malt at a
low heat so long as any percentage of moisture exceeding, say, 15 per
cent, is retained by the corn.
The regulation of temperature is shown by the diagrams, Figs. 9 and 10:
[Illustration: Fig. 9.]
[Illustration: Fig. 10.]
The distribution of the heated air in the kiln is rarely as uniform as
is supposed, the temperature of the malt on drying floor being very
different at different parts. In illustration of this, the following may
be taken from a statement by Mr. Stopes of the results of an examination
of the temperatures at different parts of a drying floor in a kiln in
Norfolk: "A malting steeping 105 qr. every four days has a kiln 75
feet by 36 feet; an average drying area of under 26 feet per qr. The
consequent depth of green malt when loaded is over 10 inches. The total
area of air inlets is less than 27 feet super. The air outlet exceeds
117 feet, a ratio of 13 to 3. The capacity of head room equals 44,550
feet cube. The area of each tile is 144 inches, with 546 holes, giving
an effective air area of some 32 inches. The ratio of non-effective
metallic surface to air space is thus 9 to 2." The Casella anemometer
gave no indications at several points, and fluctuating up and down
draughts were observable at many others, especially at two corners and
along the center. "The strongest upward draught pulsated with the gusts
of wind and ranged from 30 feet to 54 feet per minute, a down draught of
equal intensity occurring at intervals at the same spot, notwithstanding
the fact that the air was rushing in at the inlets below the floor at
the high velocity of 785 feet per minute. The temperatures of the drying
malt and superimposed air consequent upon the conditions thus indicated
were naturally as follows: At B, the place supposed to be hottest: Heat
of malt touching tiles, 216 deg.; heat of malt 1 inch above tiles, 167
deg.; heat of malt 3 inches above tiles 154 deg.; heat of malt 4 inches
above tiles, 152 deg.; heat of malt 5 inches above tiles, 142 deg.; heat
of malt on surface, 112 deg. At A, the place supposed to be coldest:
Heat of malt next tiles, 174 deg.; heat of malt 2 inches above tiles,
143 deg.; heat of malt 4 inches above tiles, 135 deg.; heat of malt on
surface, 104 deg.; the heat of the air 3 feet above tiles, 84 deg.; the
heat of the air 5 feet above tiles, 82 deg. Fig. 9 shows the temperature
at twenty-six points close to the tiles, taken with twelve registered
and accurate thermometers in the space of fifteen minutes." These and
other similar tests have led to the conclusion that the best malt drying
cannot be done on a single floor.
Fig. 10 is a similar diagram showing the temperatures on a drying floor
of kiln at Poole, Dorset, altered to Stopes' system of drying. The
temperature at different depths of the drying grain was as follows: Malt
at surface of tiles, 142 deg.; malt at 1 inch above tiles, 142 deg.;
malt at 2 inches above tiles, 142 deg.; malt at 4 inches above tiles,
141 deg.; malt on surface, 140 deg.
The advantages of the Saladin system over that hitherto working in
Britain are numerous, and are thus enumerated by Messrs. Stopes & Co.
who are agents for M. Saladin: The area occupied by the building does
not equal one-third of that otherwise required. The actual growing-floor
space is only about one-seventh, and the number of workmen is ruled
necessarily by the size of the house, but on an average is reduced
two-thirds; but the employment of much more power is necessary, and the
power is used at more frequent intervals. The use of plant and premises
is continuous, the processes of malting being equally well performed
during the summer months. The further advantage of this is that brewers
secure entire uniformity in age of malt. By the English system the
stocks of finished malt necessarily fluctuate largely. All grain is
subjected to the same conditions of surrounding air, exposure, and
temperature. The volume of air supplied to the germinating corn is
entirely under control, as are also its temperature and humidity. When
germination is arrested and the green malt is drying, the double kilns
insure control of the temperatures of the corn in the kilns. The
infrequency of turning the germinating grain benefits the growth of the
roots and the development of the plumule, besides saving much labor. No
grains are crushed or damaged by the feet or shovels of workmen. The air
supplied to the corn can be inexpensively freed from disease germs
and impurities. The capital needed for malting can be reduced by the
diminished cost of installation, and the reduced stocks of malt on hand.
The quality of the malt made is considerably improved. The percentages
of acidity are much reduced. The stability of the beer is increased,
and a greater percentage of the extractive matter of the barley is
obtainable by the brewer.--_The Engineer_.
* * * * *
NON-SPARKING KEY.
Profs. Ayrton and Perry lately described and exhibited before the
Physical Society their new ammeters and voltmeters, also a non-sparking
key. The well known ammeters and voltmeters of the authors used for
electric light work are now constructed so as to dispense with
a constant, and give the readings in amperes and volts without
calculation. This is effected by constructing the instruments so
that there is a falling off in the controlling magnetic field, and a
considerable increase in the deflecting magnetic field. The deflections
are thus made proportional to the current or E.M.F. measured. The
ingenious device of a core or soft iron pole-piece, adjustable between
the poles of the horseshoe magnet, is used for this purpose. By means of
an ammeter and voltmeter used conjointly, the resistance of part of the
circuit, say a lamp or heated wire, can be got by Ohm's law. Profs.
Ayrton and Perry's non-sparking key is designed to prevent sparking with
large currents. It acts by introducing a series of resistance coils
determined experimentally one after the other in circuit, thereby
cutting off the spark.
* * * * *
NEW INSTRUMENTS FOR MEASURING ELECTRIC CURRENTS AND ELECTRO-MOTIVE
FORCE.
By Messrs. R. E. CROMPTON and GISBERT KAPP.
[Footnote: Paper read before the Society of Telegraph Engineers, 14th
February, 1884.]
In consequence of the rapid development of that part of electrical
science which may be termed "heavy electrical engineering," reliable
measuring instruments specially suitable for the large currents
employed in lighting and transmission of energy have become an absolute
necessity. As usual, demand has stimulated supply, and many ingenious
and useful instruments have been invented, the manufacture of which
forms at the present day an important industry. Mr. Shoolbred, in a
paper which he recently read before this Society, gave a full and
interesting account of the labors of our predecessors in this field.
To-day we add to the list then given a class of instruments invented by
us, examples of which are now before you on the table. We have preferred
to call them current and potential indicators in preference to meters,
considering that the latter term, or rather termination, ought to be
applied rather to integrating instruments, which the necessities of
electric lighting, we believe, will soon bring into extensive use. The
principal aim in the design of these indicators has been to obtain
instruments which will not alter their calibration in consequence of
external disturbing forces. If this object can be attained, then it will
be possible to divide the scale of each instrument directly into amperes
or volts, as the cause may be, and thus avoid the use of a coefficient
of calibration by which the deflection has to be multiplied. This is an
important consideration when it is remembered that in many cases
these instruments have to be used by unskilled workmen, to whom a
multiplication involving the use of demical fractions is a tedious and
in some cases even an impossible task.
[Illustration: FIG. 1. FIG. 2.]
All measurements are comparative. We measure weights or forces by
comparison with some generally known and accepted unit standard
weights, lengths, areas, and volumes, by comparison with a unit length,
resistance by a standard ohm, and so forth. In the same way currents
could be measured by comparison with a standard current: but this
would be a troublesome process, not only on account of the apparatus
necessary, but also because it would be a matter of some difficulty to
have a standard current always ready for use. In general, measurement
by direct comparison with a standard unit is discarded for the more
indirect method of measuring not the current itself, but its chemical,
mechanical, or magnetic effect. The chemical method is very accurate if
a proper density of current through the surface of the electrodes be
used,[1] but since it requires a considerable time, and, above all, an
absolutely constant current, its use is almost entirely restricted
to laboratory work and to the calibration of other instruments. For
practical ready use, instruments employing the mechanical or magnetic
effect of the current are alone suitable. We weigh, so to speak, the
current against the force of a magnet, of a spring, or of gravity.
The measurement will be exact if the thing against which we weigh or
counterbalance the current itself retains its original standard value.
Where permanent magnets or springs are used as a balancing force, this
condition of constancy in our weights and measures is not always fully
maintained, and to make matters worse, there is no visible sign by which
a change, should it have occurred, can be readily detected. A spring
may have been overstrained or a steel magnet may have become weakened
without showing the least alteration in outward appearance. To overcome
this difficulty, the obvious remedy is not to use springs or steel
magnets at all, but to substitute for these some other force which
should be either absolutely constant, such as the force of gravity, or
at least should, vary only within narrow limits, and this in accordance
with a definite law. This latter condition can be fulfilled by the
employment of electro-magnets.
[Footnote 1: According to recent experiments made by Dr. Hammerl, the
density of current in a copper voltameter should be half an ampere per
square inch of surface.]
[Illustration: FIG 3.]
To imitate with an electro magnet as nearly as possible a permanent
magnet, so that the former can be used to replace the latter, it is
necessary that the magnetism in the iron core should remain constant.
This could, of course, be done by exciting the electro magnet with a
constant current from a separate source. (In a recent note to the Paris
Academy of Science, M.E. Ducretet described a galvanometer with steel
magnet, which is surrounded by an exciting coil. When recalibration
appears necessary, a known standard current from large Daniell cells is
sent through this coil during a certain time, and thus the magnet is
brought back to its original degree of saturation. M. Ducretet also
mentions the use of a soft iron bar instead of a steel magnet, in which
case the current from the Daniell cells must be kept on during the time
an observation is taken.) But such a system would appear to be too
complicated for ready use. Moreover, some sort of indicator would be
required by which we could make sure that the exciting current has the
normal strength.
[Illustration: FIG 4.]
The plan we adopt is to excite the electro magnet by the whole or a part
of the current which is to be measured. Since this current varies, the
power exciting the core of the electro magnet must also vary; and since
we require the core to have as nearly as possible a permanent magnetic
force, we are brought face to face with the question, whether an electro
magnet can be constructed that has a constant moment under varying
exciting currents. This question has been answered by the well known
experiments of Jacobi, Dub, Mueller, Weber, and others. To get an
absolutely constant magnetic moment, is not possible, but between
certain limits we can get a very near approximation to constancy.
[Illustration]
The relation between exciting power and magnetic moment is very
complicated, depending not only on the dimensions and shape of the core
and the manner of winding, but also on the chemical constitution of the
iron of the core. It is not possible, or at least it has hitherto not
been found possible, to embody all these various elements into an exact
mathematical formula, which would give the magnetic moment as a function
of the exciting current; but the above mentioned experiments have shown
that within certain limits, and in the neighborhood of the point of
saturation, the relation between the two is that of an arc to its
geometrical tangent. It will be seen that for large angles the arc
increases much slower than the tangent; that is, for strongly excited
cores, a very large increase of the exciting current will produce only
a slight increase of magnetic moment. If Mueller's formula were correct
for all currents, absolute saturation could only be reached with an
infinite current. Whether this be the case or not, it is certain that
the greater the exciting current the less will a variation in it affect
the magnetic moment of the core. To imitate as nearly as possible
permanent steel magnets, it is therefore necessary to use electro
magnets, the cores of which are easily saturated. The core should be
thin and long and of the horseshoe type; the amount of wire wound round
it should be large in comparison with the size of the core.
[Illustration]
Here is a magnet partly wound which was used in one of our earliest
experiments, but which was a failure on account of having far too much
mass in the core in comparison with the amount of copper wire wound
round it. Since then we have greatly diminished the iron and increased
the copper. The cores of the instruments on the table are composed of
two or three No. 18 b.w.g. charcoal iron wires, and are wound with one
layer of 0'120 inch wire in the case of the current indicators, and
eighteen layers of 0.0139 inch wire in the case of the potential
indicator. If from the diagram, Fig. 1, we plot a curve the abscissae of
which represent exciting current, and the ordinates magnetic moment of
the soft iron core, we find that a considerable portion of the curve
is almost a straight and only slightly inclined line. If it, were a
horizontal straight line the core would be absolutely saturated, but
such as it is, it answers the purpose sufficiently well, for with a
variation of exciting current from 10 to 100 amperes the magnetic moment
varies but slightly. If a small soft iron or magnetic steel needle, _n
s_, be suspended between the poles, S N, of an electro magnet of such
proportions as described above, and the current, after exciting the
electro magnet, _e e_, be lead round the coils, DD, it will be found
that for all currents between 10 and 100 amperes the needle, _n
s_, shows a definite deflection for each current. Here we have a
galvanometer with permanent calibration. In this case the deflection of
the needle will not strictly follow the law of tangents, because the
directing power of the electro magnet is not absolutely constant; but
whatever the exact ratio between deflection and current may be, it must
always remain the same, and to each angle of deflection corresponds one
definite strength of current.
[Illustration]
The force with which the electro magnet tends to keep the needle in its
zero position, that is, in line with the poles, S N, is due partly to
the magnetism of the core, which is nearly constant, and partly to the
magnetic influence of the coils, _ee_, themselves, which is, of course,
simply proportional to the current. The total magnetic force acting on
the needle is, therefore, represented by the sum of these two forces,
and consequently not nearly so constant as might be desired in order to
get a good imitation of a tangent galvanometer with a permanent magnet.
In the diagram, Fig. 2, the curve, O A B, represents the magnetic moment
of the iron core, the straight line, ODE, that of the exciting coils per
se, and the dotted line, O F M, the sum of the two, obtained by adding
for every current, O C, the respective ordinates, CD and C A.
CF = CD + CA
The rise of this curve shows that the force which tends to bring the
needle back to its zero position increases with the current, though at a
slower ratio than the deflecting force of the current. It follows from
this that for large currents the increment in the angle of deflection is
comparatively small, and the divisions on the scale whereon the current
is to be read off would come too near together to allow accurate
readings to be taken. In other words, the range of accurate reading in
an instrument so constructed would only be limited. But it is very easy
to eliminate the magnetic effect of the coils of the electro magnet on
the needle, by introducing an opposite magnetic effect, so that only
that part of the force remains which belongs to the soft iron core
proper. One way of doing this is by surrounding the needle with a coil,
the plane of which is at right angles to the line, S N, and coupling
this coil in series with the deflecting coil, D D. If the proportions
of this transverse coil and the direction of the current through it
be properly chosen, its magnetic effect can be made to exactly
counterbalance that of the exciting coils, _e e_, without perceptibly
weakening the magnetism of the iron core. But instead of employing two
coils, one parallel and the other transversely to the zero position of
the needle, we can obtain the same result in a more simple manner with
one coil only, if this be placed at such an angle that its magnetic
effect can be substituted for the combined effects of the two coils. In
other words, we set the deflecting coil, D D, at a certain angle to the
zero position of the needle.
A similar arrangement, though not precisely for the same purpose, has
already been suggested and tried by Messrs. Deprez, Carpentier, Ayrton,
and Perry, in galvanometers with permanent steel magnets. If the coil,
D D, be so placed, the deflecting force which now acts obliquely can be
considered as the resultant of two forces, one acting at right angles to
the line, S N, as in an ordinary galvanometer, and the other parallel to
this line, but in a sense opposed to the action of the electro magnet
and its exciting coils. If the angle of obliquity be so chosen that this
latter component exactly equals the magnetic effect of the exciting
coils _per se_, an equality which holds good for all currents, then we
shall have an almost perfect imitation of a tangent galvanometer with
permanent magnets. But we can go a step further than this; we can
overbalance the exciting coils by setting the deflecting coil at a
greater angle than necessary for the mere elimination of the former, and
thus attain that an increase of current results in a slight weakening of
the field in which the needle swings, thus allowing the increment of the
angle of deflection to be comparatively large even for large currents.
In this way it is possible to obtain a more evenly divided scale than
in the case when the deflection follows the law of tangents, as in an
ordinary tangent galvanometer. This principle of overbalancing the
exciting coils is shown on diagram, Fig. 2. The straight line, O G,
represents the magnetic effect on the needle of that component of the
deflecting force which is parallel, but in sense opposed to S N;
as mentioned above, the magnetic effect of the exciting coils is
represented by the straight line, O E. The combined effect of these two
forces on the needle is represented by the line, O K, the ordinates
of which must be deducted from those of the curve, O A B, in order to
obtain the total directing force due to each current. This is shown by
the curve, O P Q, shown in a thick full line. This curve shows how
the directing force or strength of field in which the needle swings
decreases with an increasing current. That this does actually take place
can easily be proved by experiment.
Fig. 4 shows two curves; the one drawn in a full line is obtained
by plotting the deflection in degrees of the needle of a potential
indicator as abscissae, and the corresponding electromotive forces
measured simultaneously on a standard instrument as ordinates; the
dotted line shows what this curve would be with an ordinary tangent
galvanometer.
The needle of the potential indicator is mounted at the lower end of
a steel axle, to the upper end of which is fastened a light aluminum
pointer, whereby the deflection of the needle can be read off on a scale
divided directly into volts. The scale is placed within a circular dial
plate with glass cover, giving sufficient room for the pointer to swing
all round, and the needle is placed within a central tube fitting it
closely, which acts as a damper and so makes the instrument almost
dead beat. Tube and dial are in one casting. The electro magnet is of
horseshoe form fastened to a central tubular stand, which also serves
to support the two deflecting coils, one on either side of it. The tube
within which the magnetic needle swings is inserted into the stand,
which is bored out to the external diameter of the tube. The electro
magnet and deflecting coils are wound with from 50 to 100 ohms of fine
insulated copper wire, and an additional resistance coil of from 450
to 900 ohms of German silver is added, which can, however, be short
circuited by depressing a key when the instrument has to be used for
reading low electromotive forces. In this case the indication of the
pointer must be divided by ten. If a current be sent through the
instrument the wrong way, the needle turns through an angle of 180 deg., and
thus brings the pointer to the side of the dial opposite to where the
scale is. In this position no reading can be taken, and to facilitate
the sending of the current in the right direction a commutator is added,
and the same is so coupled up that when the pointer stands over the
scale the handle on the commutator points to the positive terminal
screw. There is a limit of electromotive force below which the indicator
fails to give reliable readings. For instance, an instrument wound with
100 ohms of copper wire and 900 ohms of German silver can be used for
electromotive forces varying between 300 and 3 volts, but would not be
reliable for measuring less than 3 volts.
For very exact measurements the instrument should be placed north and
south, in the same position in which it was calibrated. Two different
patterns of current indicators are on the table; one with double needles
suspended on a point in the way compass magnets are suspended, the other
with one lozenge shaped needle mounted on an axle and pivoted on jewels,
in every way similar to the needle of the potential indicator first
described.
For measurements of currents from 10 amperes upward, there is no need
to employ a complete coil as the deflecting agent; one half-coil or one
strip passing close under the needle gives sufficient deflecting force,
and thus the construction of the instrument is rendered extremely
simple. The current, after entering at one of the flat electrodes,
splits in two parts, each part passing round the winding of an electro
magnet of horseshoe form, the similar poles of both magnets pointing
toward each other and toward the needle. After traversing the winding,
the current unites again, and passes through a metal strip close under
the needle, and finally out of the instrument by the other electrode,
which lies close under that at which the current entered, but is
insulated from it by a sheet of fiber. The metal strip is set at an
angle, to balance or overbalance, as may be preferred, the magnetic
influence of the exciting coils. The effect of this overbalancing is
shown in Fig. 5, where the full curve represents the current as a
function of the deflection--obtained by comparison with a standard
instrument--and the dotted curve shows what that relation between
deflection and current would be if the law of tangents held good for
these instruments. It will be seen that, about the middle of the scale,
the dotted line coincides nearly with the full line, while at the
extreme end of the scale the dotted line is higher. From this follows,
that if we compare our indicator from which this curve was taken with
any form of tangent instrument showing an equal angle of deflection at
the medium reading, it will be seen that the needle of our indicator
will be deflected to a greater angle at high readings than that of the
tangent galvanometer. Consequently, the divisions on the scale will
be widest apart in our instruments, which greatly facilitates high
readings.
* * * * *
SECONDARY BATTERIES.
The Consolidated Electric Light Company has now completed the secondary
battery which has for some time engaged the attention of its officers,
and their regular manufacture and use for electric lighting stations
have been fairly entered upon. Among other places to which the batteries
have been sent and put into work is Colchester, where the company
has for some time had an installation at work, chiefly employing
incandescent lamps. The battery consists of lead electrodes, anode and
cathode being of the same character. They are constructed of narrow
ribbons of lead, each element being made from long lengths of the ribbon
about or nearly 0.20 in. width, rolled together into a flat cake like
rolls of narrow webbing, as illustrated by the annexed diagram, Fig.
1, the greater part of the ribbon being very thin and flat; but
intermediate thicker ribbons are also employed, as in Fig. 2, this
thicker ribbon being corrugated as shown, and affording passage room
for the circulation of the electrolyte. From four to eight coils of the
plain ribbons are between every pair of corrugated ribbons. They are
wound up together tightly, and pressed into the nearly rectangular form
shown. The bar for suspending the coil plates so made in the cells is
soldered to the coil. The object of this construction is of course to
obtain large lead surface, and of course a much larger surface is so
obtained than could be practically obtained from plain lead plates in
the same compass. A battery thus made may be seen at the offices of the
company, 110 Cannon Street.
[Illustration: FIG. 1. FIG. 2.]
A very ingenious device for cutting the battery out of circuit when
charged as much as is thought desirable is used by the company. In a
cell is an element which has a determined lower capacity than those in
the rest of the battery. Over this element is placed a gas-tight chamber
in which is a diaphgram, this diaphragm being of very flexible material
placed in the cover of the box of cells. When charging has proceeded as
long as is desirable, or proceeds too fast, hydrogen is evolved, and
this collecting in the chamber referred to acts upon the diaphragm, and
by means of a rod connected thereto, switches the current, which is
supplied to an electro-magnet and by which circuit is made through the
medium of mercury contacts. The object, of this is to save the
battery from destruction by over-charging or charging by too large a
current.--_The Engineer_.
* * * * *
ACETYLENE FROM IODOFORM.
P. CAZENEUVE publishes in the _Comptes Rendus_ a new method for the
preparation of acetylene, which consists in mixing iodoform intimately
with moist and finely divided silver. An abundant evolution of acetylene
takes place without heating. The reaction is represented by the
following formula: 2CHI_{3} + 6Ag = C_{2}H_{2} + 6 AgI. The
decomposition of the iodoform is hastened if the silver is mixed with
finely divided copper, such as can be obtained by precipitating it from
its sulphate by means of zinc.
Cazeneuve also observed that most metals which have any affinity for
iodine will decompose iodoform in the presence of water, forming
acetylene and an iodide of the metal. By the use of zinc he obtained a
liquid having a pleasant ethereal odor, and a gas mixture that contained
besides acetylene an iodine compound which burned with a purple-edged,
fawn-colored flame.
* * * * *
WHEN DOES AN ELECTRICAL SHOCK BECOME FATAL?
In this age of electricity and electric wires carrying currents of
various intensity, the question of danger arising from contact with them
has caused considerable discussion. An examination into the facts as
they exist may therefore enlighten some who are at present in the dark.
To begin with, we often hear the question asked--why is it that certain
wires carrying very large currents give very little shock, whereas
others, with very small currents, may prove fatal to those coming in
contact with them? The answer to this is--that the shock a person
experiences does not depend upon the current _flowing in the wires_, but
upon the current _diverted from them_ and _flowing through the body_.
The muscular contraction due to a galvanic current, which was first
observed in the frog, gives a good illustration of the fact that it
requires only a very minute current to flow through the muscles in order
to contract them. Thus the simple contact of pieces of zinc and copper
with the nerves generated current sufficient to excite the muscles--a
current which would require a delicate galvanometer for its detection.
What is true of the muscles of the frog holds good also for the human
muscles; they too are very susceptible to the passage of a current.
In order to determine the current which proves fatal we need only to
apply the formula which expresses Ohm's law, viz., C=E/R, or the current
(ampere) equals the electromotive force (volt) divided by the resistance
(ohm).
According to the committee of Parliament investigation, the
electromotive force dangerous to life is about 300 volts; this then is
the quantity, E, in the formula. There remains now only to determine the
resistance in ohms which the body offers to the passage of the current.
In order to obtain this, a series of measurements under different
conditions were made. On account of the nature of the experiment a high
resistance Thomson reflecting galvanometer was used, with the following
results.
When the hands had been wiped perfectly dry, the resistance of the body
was about 30,000 ohms; with the hands perspiring ordinarily it fell to
10,000 ohms; whereas when they were dripping wet it was as low as 7,000
ohms. Our readers can judge this resistance best when we state that the
Atlantic cable offers a resistance of 8,000 ohms.
Taking an ordinary condition of the body, with the hands perspiring as
usual, we would have the resistance equal to 10,000 ohms. Applying the
two known quantities in the formula, we get:
C = (300 / 10,000) - (1 / 33.333+)
This means, therefore, that when the electromotive force or potential is
great enough to send a current of 1/33 ampere through the body, fatal
results will ensue. This current is so minute that it would deposit only
about 6 _grains_ of copper in _one hour_, a grain being 1/7,000 of a
pound.
Let us now compare these figures with some actual cases, taking as
an example a system of incandescent lighting. In these systems the
difference of potential between any two points of the circuit outside of
the lamps does not exceed 150 volts. Taking this figure, therefore, it
will be seen that under no circumstances can the shock received from
touching these wires become dangerous--not even by touching the
terminals of the dynamo itself; because in neither case can a current be
driven through the body, sufficient to cause an excessive contraction of
the muscles.
In a system of arc lighting, however, we have to deal with entirely
different conditions; for, while in the incandescent system the adding
of a lamp, which diminishes the resistance, requires no increase of
electromotive force, the contrary is the case in the arc light system.
Here every additional lamp added to the circuit means an increase in
resistance, and consequent increase in electromotive force or potential.
Taking for example a well known system of arc lighting, we find that the
lamps require individually an electromotive force of 40 volts with a
current of 10 amperes. In other words, the difference in potential at
the two terminals of every such lamp is 40 volts. Consequently, if the
circuit were touched in two places, including between them only one
lamp, no injurious effects would ensue. If we touch the circuit so as
to include two lamps between us, the effect would be greater, since the
potential between those two points is 2 x 40 volts. We might continue
in this manner touching the circuit until we had included about 7 or
8 lamps, when the shock would become fatal, since the point would be
reached at which the difference of potential is great enough to send a
dangerous current through the body.
Up to this point we have assumed that, while touching two points in the
wire, the rest of the circuit is perfectly insulated, so that no current
can leak, in other words, that the circuit is nowhere "grounded." If
this is not the case we may, under suitable conditions, receive a
shock by touching only _one_ point of the wire. This becomes clear
by considering the current to leak from another spot of different
potential, to pass through the ground and into the body; thus, on
touching the wire the body virtually makes a connection between the
two points of the circuit. In clear dry weather such leaks are
insignificant; but in damp and rainy weather, and with poor insulation,
they may rise to such a point at which it would be dangerous to touch
the circuit even with one hand, the leaks being sometimes so great as
to cause the lamps to burn in a fitful, desultory manner, and to go out
entirely.
There is still another factor which enters into the discussion of the
danger of electric light wires. This must be looked for in the fact that
the physiological effects are greatest at the moment of the opening or
the closing of the circuit; or in a closed circuit they are the more
marked when the flow of current stops and starts, or diminishes and
increases. In dynamo electric machines the current is not absolutely
continuous or uniform, since the coils on the armature being separated a
distance cause a slight break or diminution of the current between each.
This break is so short that it does not interfere with the practical
work for lighting; in some constructions, nevertheless, the distances
apart is so great that, while not interfering with light, its effects
upon the muscles are greatly increased over those of other constructions
which give a more uniform current.
All these statements might lead to the conclusion that arc light wires
are dangerous under any circumstances; but this is not the case. The
first and only requisite is, that they be perfectly insulated. When thus
protected accidents from them are impossible, and all mishaps that have
occurred through them can be traced directly to the lack of insulation.
Nevertheless, we would warn our readers against experimenting upon arc
wires by actual trial, because unforeseen conditions might lead to
disagreeable results.
* * * * *
ROBERT CAUER'S STATUE OF LORELEI.
The statue of Lorelei, the mythical siren of the Rhine, represented in
the annexed cut, which is taken from the _Illustrirte Zeitung_, was
modeled by Robert Cauer, of Kreuglach on the Rhine. He was born at
Dresden in 1831, and is the son of the well-known sculptor Emil Cauer,
and a brother of the sculptor Karl Cauer.
[Illustration: LORELEI STATUE BY ROBERT CAUER.]
* * * * *
REDUCING AND ENLARGING PLASTER CASTS.
Ordinary casts taken in plaster vary somewhat, owing to the shrinkage of
the plaster; but it has hitherto not been possible to regulate this
so as to produce any desired change and yet preserve the proportions.
Hoeger, of Gmuend, has, however, recently devised an ingenious method
for making copies in any material, either reduced or enlarged, without
distortion.
The original is first surrounded with a case or frame of sheet metal or
other suitable material, and a negative cast is taken with some elastic
material, if there are undercuts; the inventor uses agar-agar. The usual
negative or mould having been obtained as usual, he prepares a gelatine
mass resembling the hektograph mass, by soaking the gelatine first, then
melting it and adding enough of any inorganic powdered substance to give
it some stability. This is poured into the mould, which is previously
moistened with glycerine to prevent adhesion. When cold, the gelatine
cast is taken from the mould, and is, of course, the same size as the
original. If the copy is to be reduced, this gelatine cast is put in
strong alcohol and left entirely covered with it. It then begins to
shrink and contract with the greatest uniformity. When the desired
reduction has taken place, the cast is removed from its bath. From
this reduced copy a cast is taken as usual. As there is a limit to the
shrinkage of the gelatine cast, when a considerable reduction is desired
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