THE MONTAUD ACCUMULATOR.
This accumulator is of the Plante type, and is modified so as to obtain a more rapid formation, a larger surface, and a symmetrical distance of the plates from each other. If into an alkaline bath saturated with litharge (added in excess) we plunge two lead electrodes and pass in a current of suitable tension and intensity, there is deposited upon the anode a layer of peroxide of lead varying in thickness with the intensity of the current, and more or less rich in oxygen according to the intensity of the bath, while the cathode is covered with a stratum of reduced lead. The liquid of the bath supplies material for both deposits, while in galvanoplastic operations the anode supplies it to the cathode. The principle of the formation consists in introducing in an efficacious manner currents of a great intensity, and thus abridging its duration.
Of two plates thus treated, the one becomes positive, and is covered with a thick layer of peroxide of lead. On leaving the bath it undergoes various preparations and several washings, and is then fit to be mounted along with others to form an accumulator ready to be charged and to work. The second, or negative, plate is covered with a thick sponge of lead. It is carefully washed, preserved in water with exclusion of air, and submitted to a very considerable pressure. After this operation it presents the appearance of ordinary sheet lead, but though the physical porosity has disappeared, the chemical porosity is intact, and this alone comes into play in accumulators. When a negative plate is constructed in this manner, it is ready to be combined with the positives to form an accumulator.
The inventor has sometimes put into the bath at the positive pole negative plates prepared as just described. They become very easily peroxidized, but they have the grave defect of requiring two preparations in place of one. To secure an accumulator against any leakage from plate, the solderings and the entire plates must be submerged in the liquid, so that nothing projects up out of the acidulated water except two strong rods for making contact. These rods are covered with an insulating varnish from their origin to above the point where they issue from the liquid. The plates are of a rectangular form (Fig. 1). They are sloped out at one corner, and as two plates in juxtaposition are cut together, when they are separated the sloping out of the one serves for the handle of the other. This handle is doubled back on the plate which is suspended in the bath, so that the part which has to be soldered does not undergo any preparation. A hole pierced in this corner of the plate serves to receive a square rod of lead, which connects the plates together and supports one of the poles or contacts of the accumulator. At the point of soldering the doubled-down handle gives a double thickness, and the margins of the plate are folded in such a manner as to insure their solidity.
FIG. 1.
The sloped out corner affords the free space necessary for the rod of the opposite pole, and one and the same plate may be indifferently connected either to the + or the - at the right or the left. The plates are made of four different sizes: No. 1, 19 of which serve for an accumulator of 1 square meter; No. 2, 21, 25, or 29 of which serve for accumulators of 2, 3, and 4 square meters; No. 3, which with 21, 25, or 29 plates composes accumulators of 5, 6, and 7 square meters; and No. 4, which with 21, 23, 25, 27 or 29 plates forms accumulators of 8, 9, 10, 11, and 12 square meters.
As the plates are entirely submerged in the liquid their entire surface is active, and the entire surface being absolutely flat, it is sufficient to preserve their respective distance at any one point in order to have it everywhere alike. The weight of the plate depends on the intended duration of the plate and its capacity. As for the negative plate, its thickness is the most important factor of its capacity. The proportion has yet to be established for daily practice. The inventor uses in practice positive plates of 0.002 meter in thickness. On the other hand, the negative plates have a body of only 0.001 meter in thickness, their greater thickness being due only to the deposit of compressed lead. The rod which fixes the plate to each pole (Fig. 2) is formed of a special alloy of lead and antimony, not attacked by acid. This gives rigidity to the rod, and hinders it from binding when the accumulator is taken out of its case. The copper piece which surmounts it is fitted at its base with an iron cramp, which is fixed in the lead, and above which is a wide furrow with two grooved parts, which being immersed in the lead hinders the copper from slipping round under the action of the screw. The rod is square, and is cast in a single piece. Against one of its surfaces the ends of the connected plates press flatly up. A square form has been selected to give more surface for soldering. The soldering is autogenous (as in the lead chambers at vitriol works). The soldering, as well as the entire plates, is entirely immersed in the liquid, and to prevent any leakage an insulating varnish, perfectly proof against the acid and the current, is laid over the rod from the part soldered upward.
FIG. 2.
If it is wished to lift the accumulator from its chest for any verification, hooks passing between the plates seize hold of the rods, and thanks to the rigidity of the antimony lead, they effect the removal of the apparatus without bending the rods in the least. All the parts of the plates must be kept at exactly the same reciprocal distances, and a difference of only 0.001 meter between two points is sufficient to affect the yield considerably. For an insulating material, wood, when plunged in dilute acid, is preferred by the inventor. He makes a comb of wood, the teeth of which vary according to the thickness of the plates to be lodged between them. Fig. 3 represents a comb having 15/10 of a millimeter for the negative plates and 25/10 for the positive plates.
FIG. 3.
This appliance, which is 0.01 meter in thickness and 0.02 meter in width in the back, is made very cheaply by machinery. The weight of the accumulator bears entirely upon the back of the combs, which are all placed back downward, and the number of which varies according to the size of the plates. Small combs of wood clasp the plates at their extremities, and make the entire accumulator quite compact and manageable. The entire accumulator is shut up in a wooden chest, which the outer teeth of the comb serve to insulate from the leaden chest, and to prevent any loss of electricity along the sides.
Fig. 4 shows the arrangement of the side combs. A single glance at this figure shows that it would be difficult to have more surface without having recourse to curved, undulated, or folded plates, in which the distances are variable, and consequently defective. In the Montaud accumulator, the weight is simply proportional to the intended duration. For the notion, "So much capacity and so much yield per kilo.," Montaud substitutes the notion, "So much capacity or yield per square meter, the weight not being taken into consideration." These Montaud accumulators are classified as follows: They have from 1 to 12 square meters of surface, and the number corresponding to the surface indicates its weight of useful lead, its manner of charging, its capacity, and its manner of discharge.
FIG. 4.
According to the inventor's experiments, the square meter of active surface can receive a charging current of 10 amperes, and furnish on discharging a current of the intensity of 20 amperes. For a "No. 10" accumulator we have an active surface of 10 square meters, a charging current of 100 amperes, and on discharging a current of 200 amperes. A square meter of lead of the thickness of 0.001 meter weighs about 11 kilos.
As both surfaces of the lead are utilized, their weight is reduced to 5½ kilos. A No. 10 therefore requires 55 kilos. of useful lead. It will be seen that to increase the thickness of the sheet of lead merely augments the duration of the accumulator, without affecting its capacity or its manner of charging and discharging. Nos. 1, 2, 3, and 4 may be placed in vessels of stoneware, glass, or ebonite, or in boxes of pitch pine, painted with three coats of gum lac and lined with sheet lead. Nos. 5 to 12 are only sent out in pitch pine boxes lined with lead. The box is supported on feet of porcelain of the shape of a mushroom. If a drop of water falls upon this foot, it cannot give a communication with the earth, since, falling upon the broad part of the mushroom, it will glide off without running along the foot, which serves as the stalk of the mushroom. A slip of glass is placed under each foot; the part which supports the mushroom is covered with an insulating varnish, which prevents the formation of climbing salts and preserves the screws from rust. A common layer of insulating varnish is applied under the head of the mushroom.
As regards the advantages of the Montaud accumulator we notice, first, its longevity. Dr. D'Arsonval points out that the accumulators of the Plante class have a great advantage over the Faure type as regards duration, and that the most striking quality of the Montaud accumulator is its longevity. The inventor has in his possession positive plates, five to six years old, completely peroxidized, though there remains in the interior a thin core of metallic lead sufficient to give passage to the current. The adhesion of the peroxide is such that to detach it, it must be beaten with a hammer upon an anvil. The next four points—i.e., the rapidity of charge; the yield, much greater than that of any other system in proportion to its surface; its small weight in comparison with its yield; and its capacity, which for an equal weight is greater than that of any other accumulator. In his experiments in September, 1885, Dr. D'Arsonval obtained with an accumulator of 2 square meters of surface:
Useful capacity 40 ampere hours.
Total 62 " "
Surface 2 square meters
Charge 10 amp. per sq. meter.
Discharge 20 " " "
Useful weight of lead 10 kilos.
Representing a total capacity of six ampere hours per kilo., and of a discharge of 5 amperes per kilo., or a total capacity of 81 ampere hours per square meter, and a useful capacity of 20 ampere hours per square meter. Subsequently the modification of the negative plate has greatly improved these figures, which will certainly become much more advantageous in future. The total capacity of an accumulator having exactly 1¾ meters of surface has become 87 ampere hours, which if referred to an accumulator of 2 square meters of surface, would give the following results:
Useful weight of lead per sq. meter 5½ kilos.
Total capacity of useful lead per kilo 9.1 amp. hr.
Total capacity per sq. meter 50 "
Useful capacity of per kilo of useful lead 6.23 "
Useful capacity per square meter 34.30 "
Current of charge per square meter 10 amp.
Current of charge per kilo, of useful lead 2 "
Current of discharge per sq. meter 20 "
Current of discharge per kilo, of useful lead 4.56 "
The next advantage of the Montaud accumulator is the ease with which it can be taken out of its box and repaired without special tools and experience. A capital defect in this respect has hitherto much interfered with the use of accumulators. In case of accidents, several kinds of which are possible, it is found very difficult to rectify the apparatus. The Montaud accumulator is much less liable to accidents, on account of the firmness and compactness of its construction, and if any accident happens, the repairs are simple and easy. Lastly, the stout framework secures the apparatus from any accident due to a disproportionate charge or discharge. The peculiarities of the combs and rods already described solve this problem. On September 8, 1885, Dr. D'Arsonval, professor at the College of France, wrote as follows: "The Montaud accumulator is of the Plante type, and is extremely well conceived from a mechanical point of view. The wooden combs prevent the plates from coming in mutual contact, and give the apparatus great solidity. The process of formation is ingenious and rapid. To give 1 square meter a capacity of 20 ampere hours, there is required only a quarter of an hour's treatment.
"To obtain the same result by Plante's method, months are required. The entire experiments have been effected with No. 2, which has a surface of two square meters. This apparatus, if charged to saturation, gives 62 ampere hours as its total capacity, and, as in the Plante, this capacity constantly increases with use. The normal rule for the charge is 10 amperes per square meter, and for the discharge double this quantity. This apparatus has always given me on discharging 40 amperes at the E.M.F. of 1.85 volts during 60 or 65 minutes. The charge is effected in two hours up to 20 amperes, without any appreciable loss of electricity.
"The points to be aimed at in an accumulator are longevity and energy, or, rather, rapid yield per kilo. From both points of view accumulators of the Plante type (and consequently those of Montaud) are far superior to those of the Faure type. My opinion, therefore, is that the Montaud accumulator is very practical, that it is a great improvement on the Plante type, and that it can compete successfully with the other systems in use."—Revue Internationale de l'Electricite.