Faure's Secondary Battery.— Of those elements in which the process of charging is shortened, we have to name in the first place that constructed by Faure, which has attracted much attention and has met with considerable success.
It consists of two leaden strips, one of them 600 millimetres long by 1 millimetre thick, and the other 400 millimetres long by 0.5 millimetre thick. It is manifest that the "storage capacity" of such a battery will depend largely upon the thickness of the layers of dioxide and of spongy metallic lead, which are formed on its plates, for the thicker these layers the more chemical action will they develop in being reduced to sulphate, and the more chemical action will they absorb in being changed back again into oxide and metal respectively. Hence the repeated reversed charging employed by Plante in preparing his cells.
A very simple and ingenious method of saving the loss of time and energy involved in this preparation is the characteristic feature of the element devised by M. Camille Faure. He coats both plates before rolling them up with a paste of red oxide of lead (minium), made into a paste by diluted sulphuric acid. The large plate receives 800, the small plate 400 grammes. The minium is then covered with parchment, and the whole covered over with felt. It is placed in a cylindrical leaden vessel, having its inside coated with minium and felt. Such an element weighs 8,500 grammes without the liquid. The form which Reynier has given to the Faure element is shown in Fig. 417. The leaden vessel is replaced by a glass cylinder, and the felt by a texture which is not destroyed so quickly. As soon as the plates coated with minium are immersed in the diluted sulphuric acid, the minium is converted into lead dioxide and lead sulphate. The current has now only to complete the formation of lead dioxide on the one plate, and to reduce the compounds of lead on the other. According to Uppenborn, a Faure's element has an E.M.F. of two volts and weighs 25 kilogrammes. With three Siemens' machines (model D2) 150 elements can be charged in ten hours; if left unused they lose 1.5 to 2 per cent. per day.
On the first action of the charging current, the sulphate of lead on one plate is reduced to a sponge of metallic lead, while that on the other is oxidised into peroxide. This is the only difference between the "secondary battery" of Plante and the "storage battery " of Faure. Both operate on the same principle and in the same way, with probably some considerable improvement in efficiency, i.e. capacity, in the Faure arrangement. Both batteries are frequently made in the form of numerous flat plates covered with some woven fabric, and packed near together in a rectangular box filled with dilute acid. The sole novelty in the Faure device is in the use of the porous coating of decomposable substance, by which a thick layer of active material can readily be obtained on both plates of the battery. The Faure cells as they are now constructed for industrial use are rectangular in shape, and are arranged in rectangular boxes of wood impregnated and heavily coated with an asphalte varnish, which enables them to withstand the action of the acid solution which fills them. The weight of a single cell of such a battery is about ninety to one hundred pounds.
The great interest which they have excited at the present time arises largely from two causes: first, the enormous improvement in dynamo-electric machines, by reason of which electric currents can be supplied at a small fraction of what they used to cost when they were obtained only from galvanic batteries; and secondly, the great need developed in the attempts to apply the cheap electricity furnished by dynamo machines to various uses, for some means of storing the electric force either actually or practically.
In order that this desired result should be obtained in a way commercially valuable, several conditions must be fulfilled: (1) The storage must not involve any great loss of energy in the charging; (2) the stored energy should be retained with little loss; (3) the cost of the storage apparatus should be moderate; (4) the apparatus should be within moderate limits of bulk and weight; and (5) it should be enduring, and not wear out so as to require frequent replacement.
The most interesting tests of the Faure battery, with a view of determining in how far it fulfilled these conditions, were made at the Conservatoire des Arts et Metiers in Paris, by a committee of which M.Tresca was president, and MM. Allard, Le Blanc, Jubert, and Pottier were members. An extensive extract from the report of this committee to the French Academy will be found in the Telegraph Journal and Electrical Review, of London, for March 18, 1882, vol. x., p. 196.
Passing by all details of the experiments, we will only note the general facts and results. The battery experimented upon consisted of 35 cells weighing about 95 pounds each, or in all 3,325 pounds, say 1 1/2 tons. It was charged by a Siemens dynamo-electric machine, which absorbed the mechanical energy of 1.558 horse-power during 22 hours 45 minutes, which would be equal to one horse-power for 35 hours 26 minutes, or in foot-pounds 70,158,000. Of this mechanical energy 34 per cent. was expended in useless work in the machine and battery during the operation of charging, and 66 per cent. was stored as chemical energy in the battery. Of this stored energy, 60 per cent. was recovered as electric energy. This would amount to about 27,782,700 foot-pounds, or one horse-power for 14 hours 4 minutes. In other words, the actual work of one horse for 35 1/2 hours, after being stored in 1 1/2 tons of battery, could be recovered to the extent of about 14 hours' work of one horse, or the equivalent of the same in electric or other energy. Thus, Mr. Edison's 16-candle electric lamps require about one-sixth of a horse-power each, and therefore six of them could be run for 14 hours with the energy stored in this battery as above stated. Mr. Edison's smaller lamps, which give about eight candles each, or the same light as an ordinary German student's lamp, require but half as much power, and thus six of them could be run for 28 hours by this same battery.
This is, of course, not a high degree of efficiency; but, as the above-named committee remark in their report, "In many cases the loss would be fully counterbalanced by the advantage of having at hand and entirely at one's disposal so abundant a source of electricity."
The occasion of the losses experienced in the storage battery, and also the exact character of the actions, chemical and electrical, which go on in it, are very fully developed in a paper on "The Chemistry of the Plante and Faure Accumulators," by J.H.Gladstone and Alfred Tribe, in Nature, of January 25 and March 16, 1882. The main sources of loss there shown are, first, local action between the negative lead plate and the peroxide of lead deposited upon it; and second, the resistance of the oxide and sulphate to the passage of the current, by reason of which energy is lost by being converted into useless heat in the battery both at charging and discharging.
By so regulating the discharge of the battery as to reduce this loss, and by giving seasons of repose in which the battery recovers some of its deterioration, Messrs. Ayrton and Perry succeeded in recovering 82 per cent. of the power put into one of these batteries. A single cell, weighing 81 pounds without the dilute acid, yielded, in three discharges of six hours on three successive days, an electric current whose total energy was 1,440,000 foot-pounds, which represents about one horse-power exerted for about three-quarters of an hour. This is almost double the efficiency per weight of battery shown by the French experiments, and the recovery of 82 in place of 60 per cent. of the stored energy would indicate a much greater efficiency in this respect also.
Experiments in using the Faure battery for industrial purposes have already been made in various directions. It has been employed to run street cars and other vehicles (including even velocipedes), to propel boats, to work sewing machines and others requiring a small amount of power, to illuminate houses and single rooms, and also steamers and railway carriages. As yet it has only been shown to be economically valuable where peculiar conditions protect it from competition with other means of effecting the same results more directly. Thus it has been used in France at the establishment of M.Duchesne-Fournet, where linen cloth is bleached by exposure to sunlight on bleaching-greens, to run a train carrying out the cloth from the factory to the green, and to wind in the cloth from the green after it has been bleached. An ordinary steam engine could not be used in this case on account of its smoke and cinders. Again, in railway cars it may be more convenient to use a Faure battery than to have a dynamo-electric machine, either run by a special engine or by the motion of the train. The latter would of course be impracticable without some storage arrangement to provide a light when the train stopped.
Indeed, as a regulator of electric currents, to equalise them, or bridge over brief interruptions of the generating machines, a storage battery would seem to have a wide application.
As is well known, a number of these Faure batteries were recently used to maintain four incandescent lights when required on the steamer Labrador, during her passage to New York.
Modifications of the Faure Element.—To give the lead plates a loose surface, G. Schulze, of Strasburg, covers them with powdered sulphur, and then heats them. If now the plates be immersed in dilute sulphuric acid, and the current allowed to pass, at one plate the sulphur will combine with the hydrogen and escape as sulphuretted hydrogen, leaving spongy lead behind, whilst at the other plate lead sulphate and lead dioxide will be formed. The elements consist of plates 23 centimetres high, 12 centimetres wide, and 0.5 millimetre thick, which are suspended and connected as shown in Fig. 418. The lead of an accumulator consisting of thirty plates weighs 8 kilogrammes. The total weight, including the fluid, is 10.5 kilogrammes. When charged, the element possesses a resistance of 0.005 ohm, which is increased during the discharge to 0.015 ohm, by an E.M.F. of 2.15 volts. De Calo uses for his secondary elements plates consisting of spongy lead coated with minium and placed in little sacks. Kornbluh uses lead wire gauze coated with minium; ten plates of 6 millimetres thickness are joined to form one element. The secondary element constructed by Boucher is shown in Figs. 419 and 420. The negative electrode here consists of sheet zinc z bent into a U-shape. Within it is suspended the waved leaden plate P, coated with litharge; and, to prevent contact, parchment F is wrapped round it. The several plates are fastened to a frame which can be moved up and down. Each element receives 300 grammes of zinc sulphate, and separates zinc out during the charge, forming lead dioxide at the lead plate. The charged element then consists of lead dioxide, zinc, and sulphuric acid. If the plates were not taken out of the liquid, the zinc would again dissolve in the sulphuric acid; to prevent this the plates are arranged as shown in the figure. During the discharge zinc sulphate is formed in the element, and at the same time the lead dioxide is reduced. According to Bottcher, the element furnishes a current after discharge, on account of the galvanic element, consisting of lead, zinc, and zinc sulphate; this current cannot, however, be of very long duration, as polarisation will quickly set in. For practical purposes the form would have to be altered.
