A cheap modification of the Daniell cell. A glass jar has at the bottom a copper plate consisting of 4 to 6 leaves of thin sheet copper, set on their edges in a starlike shape, a copper wire being attached to the copper rivet which holds the leaves together. A mass of crystals of sulphate of copper is filled in and laid on the top of the copper electrode an inch or so above its top. The negative plate is a variously shaped plate of cast zinc hung from the edge of the jar and reaching about 2 inches from the top into the fluid. Water is poured in until it covers the zinc, and the battery is complete. The sulphate of copper deposits its metallic copper on the copper leaves and liberates sulphuric acid, which rises and attacks the zinc, setting free sulphate of zinc. The sulphate of zinc solution being of greater density remains near the bottom, and the sulphate of zinc solution stays near the zinc. When the cell is left too long on an open circuit the two solutions tend to mix, and copper is deposited on the zinc. The sulphate of zinc finally saturates the top solution, which has to be partly drawn off and replaced by fresh water and crystals of sulphate of copper dropped into the jar to take the place of that which has been decomposed. Electromotive force 1 volt, current from 3∕10 to 5∕10 of an ampere. The practical working of this cell will be treated of later on in these pages.
Fig. 61.
The Gethins (Fig. 61) and the Hussey bluestone cells both have the zincs standing in porous cups (shown by dotted lines), which in turn are supported half-way down the jar, generally resting on the copper strip acting as a porous partition between the fluids. The zinc stands in a solution of zinc sulphate, or a weak sulphuric acid solution. The internal resistance is low, and the current large, being from 1 to 5 amperes. These cells are the ideal bluestone cells for charging storage batteries requiring very little attention. The special Gethins cell shown in the figure has the copper made with a collar, which encircles the porous cup, and thereby lowers the internal resistance of the battery. The voltage not being over 1 volt, however, renders these cells hardly suitable for direct connection. Five cells connected in multiple would give all of 10 amperes of current, and 1 volt, and a number of these multiple groups could be connected in series for a higher voltage.
Gordon Battery
is similar in operation to the Edison-Lalande, but differs in details of construction. The zinc is a heavy ring suspended outside, but not touching a perforated tin cylinder closed at the bottom, containing the oxide of copper in flakes. Its internal resistance is slightly higher than the Edison-Lalande cell, otherwise there is little choice. The 6 × 8 size is excellent for coil work, giving 250 actual ampere hours and remaining on open circuit for long periods without deterioration.
Edison-Lalande Cell.
This is a practical form of the old Lalande-Chaperon cell, and gives a steady, large current, being of low internal resistance, but is of low electromotive force, being less than .70 volt on closed circuit of medium resistance. Being of low internal resistance, however, its output is large—three cells of the type S; internal resistance, 0.025 ohm. Capacity, 300 ampere hours, will about equal one cell type E 5 of the Chloride Storage Battery. The elements of this cell consist of positive plates of amalgamated zinc, suspended on each side of negative plates of the black oxide of copper in an electrolyte solution of caustic potash. In action the decomposition of water forms an oxide of zinc from the positive element, which with the potash in combination leaves a soluble salt of zinc and potash. The hydrogen of the water acts on the oxide plates to form metallic copper, thus really reducing, instead of increasing, the internal resistance of the cell. A layer of heavy paraffin oil is poured on top of the solution to prevent the action of air.