The dry cell
The dry cell is a form of Leclanche cell in which the ammonium chloride solution is replaced with a jelly composed of starch, flour and ammonium chloride (Fig. 34.6). The positive element consists of a carbon rod surrounded by a core of a compressed
mixture of manganeseuv) oxide and carbon. This is placed inside a zinc can and the space between filled with the ammonium chloride jelly. The zinc can also act as the negative element. The jelly is prevented from drying up by sealing the top of the cell
either with pitch or else by means of a metal disc insulated from the can by a fibre disc. Cells of this type give a large current and have a much shorter recovery time than the “wet” type and are used for a- great variety of purposes. Owing to local action which cannot be entirely prevented, they slowly deteriorate when not in use. Modern cells, however, have a “shelf life” of months or even years if stored in a cool place.