The containing vessel of the Edison cell is a porcelain jar having a porcelain cover, through which the connecting wires or rods of the plates enter the cell. The copper oxide plate is obtained by roasting copper turnings, which are then ground to a fine powder and mixed with 5 to 10 per cent of magnesium chloride. The oxide is then molded into plates, which are held in a copper frame in the cell, as at cc, Fig. 1; this frame being attached to the cover of the cell and forming one of the terminals, zz are the zinc plates, one on each side of the copper oxide plates. Batteries of the oxide of copper type are extensively employed in connection with spark coils for gas-engine work, and for numerous other purposes requiring continuous current, as these are eminently closed circuit batteries. They can also be used as open cir cuit batteries.
Gordon.—A copper oxide cell used exten sively for working fire, police and railway sig nals, and of economical use anywhere. Al though designed for closed circuit work it does well also on open circuits. The outer jar is of glass, porcelain or enameled ware, with a cover of the same materials, or of tin, or com pressed fibre. A perforated cylinder of tin plate is suspended in the centre of the cell by an iron rod. This cylinder is filled with black oxide of copper. On the outer circumference of the cylinder at equal distances are attached three L-shaped lugs of porcelain which support a heavy zinc ring, and at the same time insu late it from the tin cylinder. The electrolyte is a solution of caustic soda, and the surface of the cell is covered with a layer of heavy paraffin oil, which prevents the creeping over of the caustic. As commonly used these cells give six months' service before renewal is nec essary.
Two-Liquid Batteries.— Although the one liquid cells have proved to be adequately non polarizing, several forms of two-liquid cells re tain a hold on the market, and for some of them there is a large demand.
Daniell, an annular vessel of copper in the bottom of a jar is piled with crystals of copper sulphate, and within it stands a jar of porous earthenware in which is suspended a zinc bar. The electrolyte in the porous jar is dilute sul phuric acid, or, sometimes, zinc sulphate.
The electrolyte in the outer jar is a saturated solution of copper sulphate. This is a closed circuit battery which has been used extensively for telegraph work.
Gravity, a cell with the same components as the Daniell cell, but without the porous jar. The copper element is a spider-like form of sheet copper spreading its. legs over the bot tom of the jar. This copper form is completely covered with crystals of copper sulphate, or sometimes there is a perforated copper disc laid upon the spider and the copper sulphate is piled upon the disc. In the upper part of the jar is hung a thick seven-toed crowfoot of zinc— from which this form of cell is often called the crowfoot battery. The electrolyte is of dilute sulphuric acid. A concentrated so lution of copper sulphate will soon occupy the lower part of the jar, and above it will float the lighter zinc sulphate solution—with, how ever, some little diffusion *here the two solu tions meet.
Minotto, a cell in all retects like the Grav ity cell, but with a flat Mat of cloth sttiffed with sand or sawdust snugly above the copper sulphate to keep the two solutions quite separate. This battery is much used for rail way signal work, in spite of the fact that its internal resistance is very high— from four to six times that of the Gravity cell.
Fuller, the approved cell for telephone work consisting of a carbon cathode hung in a depo larizing liquid, a combination of dilute sulphuric acid and a solution of potassium bichromate. A porous inner cup or jar has suspended in it the zinc anode and a little mercury is placed in the bottom. The electrolyte in the porous cup is usually pure water; occasionally a very little sulphuric acid is added.
Grove, a cell consisting of a hollow cylinder of zinc, within which is a porous jar containing a strip of platinum. The electrolyte in the porous cup is strong nitric acid, and in the outer jar is dilute sulphuric acid. This cell is used chiefly in laboratory work.
Bunsen, a cell very similar to the Grove cell except that it has a bar of carbon in the porous jar instead of the strip of platinum.