Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

bines with hydrogen to form water. Besides this, there is a thin film of copper deposited on the surface of the within cop- per. Now, it is easy to see that Becquerel's battery would work more slowly, but far more constantly than the voltaic pile or any other battery then known. But the organic membrane was not, after all, very durable; and this was the greatest objection to this otherwise valuable battery. The Water battery, as it is called, came next. It was first prepared by M. Gassiot, and is peculiar for possessing properties of but feeble dynamic electricity, as compared with its static ac- cumulation and tension effects. This is indeed the characteris- tic also of all so called dry piles, which give an electricity in a state of tension alone. M. Gassiot employed glass cells, which were supported upon glass columns so as to render the insula- tion more complete. Thus he constructed a compound battery of 3520 zinc and copper pairs in as many cells, which were charged only by pure water. This, says M. De la Rive, during the several years it has remained set up, at all times gives elec- tric sparks at each of its poles, (which are also insulated.) The only precaution taken with this apparatus, is to pour water into the cells occasionally, so as to replace that which is lost by evaporation. In this case, it is the air that is contained in the water that oxidizes the plates so slowly or minutely, that it thus lasts and acts for years together. The Dry pile is constructed much as Volta's original moist pile; but it is not an absolutely dry pile after all, for in that case it would not act. To prepare the permanent dry pile, large, stout sheets of brown paper are coated on the one side with tin foil, which answers to the place of the zinc in other batteries, and the other side of the paper is coated with the peroxide of manganese, which answers to copper. The paper is first tinned on one side only; on the other side the manganese is spread by means of a soft brush. The powder of peroxide of manganese is prepared in a fluid paste and milk. When the sheets are dry they are cut neatly in squares for disks. These are then laid in the same order, the one above the other, so that a face of tin and another of manganese may always be in contact in all the