One of the most difficult problems that daily presents itself in large
cities is how to proceed without danger in the search for leakages in gas
mains, or in attempts to save life in houses accidentally filled with
explosive gases. The introduction of a flame into such places leads in
the majority of cases to accidents whose consequences cannot be
estimated. The reader will remember especially the explosion which
occurred some time ago in St. Denis Street, Paris, and which killed a
considerable number of persons. It has, therefore, been but natural to
think of the use of electricity, which gives a bright line without a
flame, in order to allow life-saving corps and firemen to enter buildings
filled with an explosive mixture, without any risk whatever.
[Illustration: FIG. 1.--ELEVATION (Scale 1/25).]
Several electricians have proposed ingenious portable apparatus for this
purpose, and, among these, Mr. A. Gerard, whose device we illustrate
herewith. In this system the electric generator is stationary, and
remains outside the building. This, along with all the rest of the
apparatus, is mounted upon a carriage. The operator, instead of carrying
a pile to feed the lamp, drags after him a very elastic cable containing
the two conductors. This "Ariadne's thread" easily follows all
sinuosities, and adapts itself to all circumvolutions. The entire
apparatus, being mounted upon a carriage, can be easily drawn to the
place of accident like a fire engine.
[Illustration: FIG. 2.--PLAN (Scale 1/25).]
_General Description_.--Fig. 1 shows the carriage. In the center, over
the axle, is mounted a dynamo-electric, machine, D, driven by a series of
gear wheels that are revolved by winches, MM. Upon the shaft, A, is fixed
a hand wheel, V, designed to regulate the motion. In the forepart of the
carriage are placed two windlasses, TT, permanently connected with the
terminals of the dynamo. Upon each of these is wound a cable formed of
two conductors, insulated with caoutchouc and confined in the same
sheath. Each windlass is provided with five hundred feet of this cable,
the extremity of which is attached to two lanterns each containing an
incandescent lamp. These lanterns, are inclosed in boxes, BB, with double
sides, and cross braced with springs so as to diminish shocks. Under the
windlass there is a case which is divided into two compartments, one of
which contains tools and fittings, and the other, six carefully packed
incandescent lamps, to be used in case of accident to the lanterns. At
the rear end of the carriage there is a hinged bar, C, designed to
support it at this point and give it greater stability during the
maneuvers. The stability is further increased by chocking the wheels.
[Illustration: FIG. 3.--HAND LANTERN (Scale 1/4).]
_Maneuver of the Apparatus_.--The carriage, having reached the place of
accident, is put in place, its rear end is supported by the bar, C, the
wheels are chocked, and the winches are placed upon the dynamo gearing.
Two strong men selected for the purpose now seize the winches and begin
to revolve them, and the lamps immediately light while in their boxes.
Another man, having opened the latter, takes out one of the lanterns and
enters the dangerous place, dragging after him the elastic cable that
unwinds from the windlass. Two men are sufficient to turn the winches for
five minutes; with a force of six men to relieve one another the
apparatus may therefore be run continuously.
[Illustration: FIG. 4.--POLE LANTERN (Scale 1/4).]
The dynamo, which is of strong and simple construction, is inclosed in a
cast iron drum, and is consequently protected against accident. With a
power of 25 kilogrammeters it furnishes a current of 40 volts and 7
amperes, which is more than sufficient to run two 50-candle incandescent
lamps. The winches are removable, and are not put upon the shaft until
the moment they are to be used.
The windlasses, as above stated, are permanently connected with the
terminals of the dynamos. The current is led to them through their
bearings and journals. Their shaft is in two pieces, insulated from one
another. One extremity of the cable is attached to these two pieces, and
the other to the lantern. Each windlass is provided with a small winch
that allows the cable to be wound up quickly.
[Illustration: FIG. 5.--WINDLASS (Scale 1/10).]
The two lanterns are different, on account of the unlike uses to which
they are to be put. One of them is a hand-lamp that permits of making a
quick preliminary exploration. The second is to be fixed by a socket
beneath it to a pole that is placed along the shafts of the carriage.
This lantern, upon being thrust into a chimney, shaft, or well, permits
of a careful examination being made thereof. As the handle terminates in
a point; it may be stuck into the ground, to give a light at a sufficient
height to illuminate the surroundings.
The hand lantern consists of a base, P, provided with three feet. At the
top there is a threaded circle to which is attached a movable handle, K,
that is screwed on to a ring, C. These three pieces, which are of bronze,
are connected by 12 steel braces, E, that form a protection for the
glass, M. The lantern is closed above by a thick glass disk, G. The
luminous rays are therefore capable of spreading in all directions. Tight
joints are formed at every point by rubber or leather washers.
[Illustration: FIG. 6.--LANTERN BOX (Scale 1/10).]
In the center of the lantern is placed the incandescent lamp. This is
held in a socket, and is provided with two armatures to which the
platinum wires are soldered. Two terminals, b, are affixed to the lamp
socket. Beneath the lantern there is a cylindrical box provided with a
screw cap. In one side of this box there is a tubulure that gives passage
to the electric cable whose conductors are fastened to the terminals. A
conical rubber sleeve, R, incloses the cable, which is pressed by the
screw cap, S. A special spring, Y, attached at one end to the top of the
lantern, and at the other to the cable, X, is designed to deaden the too
sudden shocks that the lantern might be submitted to, and that would tend
to pull out the cable.
As a result of the peculiar arrangement of this lantern, the lamp is
constantly surrounded with a certain quantity of air that would certainly
suffice to consume the carbons in case of a breakage of the globe without
allowing any lighted particles to escape to the exterior. Besides, should
the terminals become unscrewed, and should the conductors thus rendered
free produce sparks, the latter would be prevented from reaching the
exterior by reason of the absolute tightness of the box. In case the
incandescent lamp should get broken, the only inconvenience that would
attend the accident would be that the man who held the lantern would be
for a moment in the dark. When he reached the carriage, it would be only
necessary for him to take off the glass disk, take the broken lamp out of
its socket, insert a new one, and then put the glass top on again.--_Le
Génie Civil_.
* * * * *
Voltaic batteries containing solutions of ammonium chloride and zinc
chloride can, according to the recent researches of M. Onimus, be
converted into dry piles by mixing these solutions with plaster of Paris,
and allowing the mixture to solidify. If mixtures of ferric oxide and
manganese peroxide with plaster of Paris are employed, the electromotive
force is slightly higher than with plaster of Paris alone; and when
ferric oxide is used, the battery quickly regains its original strength
on breaking the circuit. When the battery is exhausted, the solid plaster
of Paris has simply to be moistened again with the solution.
* * * * *
THE ELECTRIC DISCHARGE AND SPARK PHOTOGRAPHED DIRECTLY WITHOUT AN
OBJECTIVE.
The study of the form and color that electric discharges exhibit,
according to the different ways in which they are produced, has already
enticed a certain number of amateurs and scientists. Every one knows the
remarkable researches of the lamented Th. Du Moncel on the induction
spark, and during the course of which he, in 1853, discovered that
phenomenon of the electric efflux which has since been the object of
important researches on the part of several physicists and chemists,
among whom must be cited Messrs. Thenard, Hautefeuille, and Chapuis.
Twenty years ago, Mr. Bertin, who was then Professor at the Faculty of
Strassburg, and who was afterward subdirector of the normal school, was
directing his researches upon the electric discharges produced by high
tension apparatus, plate machines, and Leyden jars. He thought, with
reason, that, on account of its rapidity and complexity, a portion of the
phenomenon must escape the eye of the observer, and so the idea occurred
to him to photograph the discharge in order to afterward study its forms
more at his leisure. We have recently had an opportunity of seeing a
negative which was obtained by him at that epoch; but the photographic
processes then in use probably did not allow him to obtain others that
were as satisfactory, and he had given up this kind of study, when, last
year, he had an opportunity of speaking of it to the well known
manufacturer Mr. F. Ducretet, whom he induced to take it up and employ
the new gelatino-bromide process. Unfortunately, he died before these
experiments were begun, and was unable to see the realization of his
project. Mr. Ducretet did not abandon the idea, but constructed the
necessary apparatus, and obtained the results that we now place before
our readers.
[Illustration: FIG 1.]
His apparatus, which contains no photographic objective, consists of an
oblong case, ABCD, made of red glass and resting upon an ebonite table
supported by one leg (Fig. 1). In the top of the case, as well as in the
two sides, AD and BC, are apertures that are closed by ebonite cylinders
through which slide, with slight friction, copper rods, HLN. In the leg
of the table there is a copper rack which may be maneuvered from the
interior by a pinion, and which communicates electrically with a
terminal, E. The upper part of this rack, which enters the glass case, is
threaded, so that there may be affixed to it either a metallic or an
insulating disk. The rods, HLN, are likewise threaded, so that there may
be affixed to their internal extremities balls, points, combs, and disks
of metal or of insulating material at will.
[Illustration: FIG 2.]
In short, we have here a transparent box (impermeable to photogenic rays)
into which electricity may be led by means of four conductors that are
arranged two by two in a line with each other, or in perpendicular
positions, and that may be made to approach or recede from one another by
maneuvering them from the exterior. This very simple arrangement answers
every requirement, and, upon placing a sensitized plate in the vicinity
of the conductors, permits of photographing the electric discharge
directly and, so to speak, before the eyes of the operator.
As a source of electricity, use is made of a bichromate of potash
battery of 6 elements, capable of giving 10 volts and 15 amperes. The
current from this battery is converted into a current of high tension by
means of a strong induction coil capable of giving sparks more than eight
inches in length. The discharge shown in Fig. 4 was obtained by means of
a Holtz machine. Each experiment lasted less than a second.
[Illustration: FIG. 3.]
Figs. 2 and 3 represent the efflux that occurred under; the following
conditions: The disk, P, was of metal, and was connected with the
negative pole of the induction coil; and upon it was laid the
photographic plate with the sensitized film downward, and consequently
touching the disk. This is what produced the opaque circle in the center.
Then the photographic plate was entirely covered with a thin ebonite
plate, above which there was a second one supported by small wedges, so
as to allow air to circulate between them. Finally, upon this second
ebonite plate there was placed another photographic plate, with its
sensitized film upward and directly in contact with an upper metallic
disk, and connected with the positive pole of the coil by the conductor,
L. An inspection of Figs. 2 and 3 shows that the, efflux does not possess
the same form at the two poles. We remark at the positive pole a quite
wide opaque circle surrounded by a sort of aureola composed of an
infinite number of very delicate rays, while at the negative pole the
aureola seems not to have been able to spread. We see, moreover, the same
phenomenon in examining Fig. 4 (which represents the efflux obtained by
means of a Holtz machine), but this time in a horizontal direction. The
photographic plate was here placed upon the non-conducting disk, P. As
the sensitized film was upward, it was put in contact with the balls at
the extremity of the conductors, H and N.
[Illustration: FIG. 4.]
It will be seen here again that the efflux spreads out widely at the
positive pole, while it is contracted at the other. The conducting balls
were spaced 0.04 inch apart. A spark leaped from one to the other at the
moment the current was being interrupted.
In Fig. 5 we are enabled to study with more ease a spark obtained with
nearly the same arrangement. The balls, H and N, did not here rest
directly upon the sensitized film, but upon two small sheets of tin
cemented to the extremities of the plate at 0.06 inch apart. In addition,
the source employed was not the Holtz machine, but the pile with
induction coil. Two nearly parallel sparks were obtained. It will be seen
that these are very complex. Each of them seems to be formed of four
lines of different sizes, entangled with one another and presenting
different sinuosities. Aside from this, the plate is traversed for a
space of 0.04 of an inch by curved lines running from one pole to the
other, and exhibiting numerous sinuosities.
[Illustration: FIG. 5.]
Fig. 6 represents a discharge that occurred under the following
circumstances: The disk, P, being metallic and connected with one of the
poles, there was placed upon it a thin ebonite plate of the same
dimensions as the photographic one, and then the latter with the
sensitized pellicle upward. Finally, the pellicle was put in contact with
the upper conductor, L, which terminated in a ball and was connected with
the other pole of the induction coil.
It will be seen that, despite the two dielectrics (ebonite and glass)
interposed, and the opacity of one of them, the efflux that occurred
around the disk, P, is quite sharply reproduced upon the sensitized plate
by a circle like that which we observed in Figs. 2 and 3. It will be
seen, besides, that an infinite number of ramifications in every
direction has been produced around the ball, and we can follow the travel
of the spark that leaped between the ball and disk in two directions
situated in the prolongation of one another.
Under the two principal and clearly marked lines that this spark made
there are seen two other, very pale and much wider ones, that present no
sinuosities parallel with the first.
The results of these experiments are very curious. The position of the
plates was varied in 18 different ways, as was also the form of the
conductors. We have spoken of those only that appear to us to present the
most interest. Unfortunately, notwithstanding the skill of the engraver,
it is impossible to render with accuracy all the details that are seen
upon examining the negative. The proofs that have been printed upon paper
present much less sharpness than the negative, for there are certain
parts of the figures on the glass that do not show in the print.
[Illustration: FIG. 6.]
We have been content here to make known the results obtained, without
drawing any conclusions from them. It is to be hoped that these
experiments, which can be easily repeated by means of the apparatus
described above, will be repeated and discussed by electricians, and that
they will contribute toward making known to us the nature of the
mysterious agent that will give its name to our era.--_G. Mareschal,
in La Lumiere Electrique._
* * * * *