By making use of the phenomenon of diffusion, Kousmine has succeeded in overcoming the increase in internal resistance of the bichromate ot potash battery due to the formation or crystals on the positive electrode.' The positive carbon electrode consists of 4 strips attached to the lid of the battery. The negative zinc electrode consists of a circular grating, resting on the bottom of the battery. By means of a funnel a 15° B. solution of sulphuric acid is introduced, until it just reaches the lower end of the carbon strips. A 6 to 7 per cent, solution of bichromate of potash is next introduced. The two liquids do not mix, on account of the great difference in their densities. When the battery is short-circuited, it is easy to see that chemical action only takes place close to the lower end of the carbon strips, which are gradually surrounded by a violet ring 2-3 mm. deep. Above this region the bichromate solution retains its original colour. The bichromate solution being very weak, the chromic crystals dissolve as soon as they are formed, and the positive electrode is not covered by a deposit as in other batteries. The solution of these crystals, having a greater density than the surrounding liquid, falls to the bottom.

The sulphate of zinc also falls to the bottom of the cell, causing more sulphuric acid to . rise. A cell tested by a committee of experts showed: - Height 20cm., diameter, 15cm., surface of zinc 176sq. cm., bichromate solution 6 per cent., sulphuric acid 15° B. After having been circuited for 8 1/2 hours on an external resistance of .32 ohm, and then left on open circuit for 10 1/2 hours, the cell con-tinued to work for 4 1/2 hours, when the circuit was again closed, and it gave during 13 hours 36 ampere-hours for an expenditure of 48grm. of zinc.

Lcdande- Chaperon

The inventors hoped from experiments they made that by combining zinc and an alkaline solution with an efficient depolarising solid, they could fulfil the necessary conditions for a cell which should remain mounted for a long period, like the Leclanche, whilst furnishing a constant and large current, several amperes for instance, though but of small dimensions. Following out this train of thought, the trial of metallic oxides as depolarising material, a large number of which are insoluble in alkalies, was naturally indicated. Among all those examined none seemed to supply electrodes of such capacity as oxide of copper. Peroxide of manganese gives a high E.M.F. with an open circuit, but in alkali elements, as also in sal-ammoniac elements, polarisation ensues very quickly for a duty of some importance. They did not think it worth while to follow up the examination of this combination subsequently extolled by Leuchs. The various oxides of iron, natural or artificial, turned out badly, and were not reduced in any appreciable manner in the battery. However, the small layer of oxide formed by oxidation through heat on plates of iron placed at the positive pole was reduced rapidly enough, and made good contact with depolarisers, even solids.

This quality of making with the positive electrode sufficiently good contact to allow the battery to work well, to make good contact, is very variable, not only with the nature of the oxides, but also with their physical state. Thus oxide of copper formed by roasting copper in the air is generally found to be in good condition for use; whilst chemically precipitated oxide makes far inferior contact with the electrode. The binoxide of mercury, which it would appear should show properties very much resembling those of oxide of copper, depolarises slowly and badly, whether it is used with a support of copper, iron, carbon, or even mercury. Oxides of the precious metals (silver, platinum, gold) give high electromotive forces, and depolarise regularly. Oxide of silver has given, in D'Arson-vaPs hands, an E.M.F. of more than 1 1/2 volt. Unhappily, the price and the high molecular weight of silver render its use very limited. The battery thus formed is not completely reversible; the silver reduced to oxide in the working of the battery only absorbs electrolytic oxygen in an incomplete manner, whilst with copper the absorption is complete up to perfect oxidation.

The same electromotive forces are obtained, in fact, by the use of the oxide or chloride; the latter, having a heat of formation far higher than that of the oxide, evidently will not give the same E.M.F. unless it undergoes a preliminary transformation. High electromotive forces might be hoped for with the higher oxides of nickel and cobalt obtained by an electrical recharging of elements working as secondary batteries; but these products make bad contact with the supports. Oxide of bismuth, on the contrary, which is formed by using the lower nitrate, might answer readily; but it is very inferior to oxide of copper. Binoxide of lead cannot be used.

Having ascertained in a general manner that the combination of the properties of oxide of copper and those of alkaline solutions enabled them to construct a cell which would last and give a high duty, it remained to design simple forms for different uses. The use of agglomerate depolarising solids has been much upheld. Products haying energetic depolarising properties, and offering great resistance to the dissolving action of caustic alkalies, are prepared by mixing a small quantity of oxychloride of magnesium with oxide of copper, and moulding the material on a metal support to ensure contact. This method of using the oxide readily permits of the formation of elements of small volume and large surface. It is necessary to remark, however, that under ordinary conditions, when the battery must not be recharged after running down, these agglomerate plates become, as in the Leclanche* cell, a useless residue, and the work expended in their manufacture is entirely thrown away. On the other hand, the pure metallic copper obtained by the reduction of the unmixed oxide is far from being valueless. Accordingly, it seems more practical to apply the oxide to the conducting support, which in this case should be horizontal, by its own weight alone.