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.
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.
FIG. 2. - PLAN (Scale 1/25).
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.
FIG. 3. - HAND LANTERN (Scale 1/4).
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.
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.
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.
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.