This battery conlists of an outer Teasel a (Fig. 34), containing an inner porous cell b; in the outer vessel is a. carbon plate c, packed round with broken gas • retort carbon; the zinc rod d is placed in the porous cell. A convenient battery may be made of 5 No. 9 jars, into which the carbon-plates with their binding - screws and the porous cells are placed; the outer ed up with granulated carbon to within 1 in. of the top. As to the mixture. Make a saturated solution of potash bichromate with cold water (you will find 3/4 hour sufficient to make the solution strong enough, if you give it 2 or 3 stirrings); allow it to settle, and pour off the clear solution. Take a glased earthenware pan, and mix in it sufficient of 2 parts of the above, with 1 of muriatic acid, and fill up the outer cells. For the inner cells, break up some ammonium chloride, and put 1 1/4 oz. into each cell, then 1 oz. muriatic acid into each, and fill up immediately with water to the level of the granulated carbon. Couple up with stout wire, and a good light will be the result, providing you select a lamp giving low resistance. The battery requires replenishing about every 6 or 8 weeks; but this need not be if you arrange to remove the zincs from the porous cells when the light is not required.

The light gets fainter after strength if a rest is given. A layer of mercury at the bottom of the porous cell assists in keeping the zinc amalgamated and in working order. About 5 cells 8 in. by 5 in. diameter will maintain a low-resistance. Swan lamp of 5 candles' power for 40 hours, but the light will not be full 5 candles. The solutions for recharging do not cost more than 3d. to 6d in 8 or 9 months, according to use. This battery can be sealed if used for medical coils, a testing cell, or firing fuses.

Fig. 34.

Fig. 35 shows a transverse section of a cell, which better illustrates the relative positions of the. parts:. a, outer cell; b, porous cell; c, zinc; d, carbon plate; e, granulated carbon. The black spots on the carbon-plate and zinc show the position of binding screws with wires attached. Couple up zinc of one cell to carbon of next, throughout, with which means the zinc is brought opposite to each side of the platinum plate. But it is advantageous, instead of bending a long strip of zinc, to employ 3 shorter pieces: 1 to be put at the bottom of the containing jar, and 2 others resting on this to form the vertical sides. This is less expensive to make, and more economical to use. Binding - screws, attached to the zinc plate and the platinum, form the 2 electrodes. The excitants are strong nitric acid in the porous cell with the platinum, and acidulated water with the zinc. The form illustrated is most convenient on the score of portability, but the greatest power is obtained by arranging the battery in cylindrical vessels like a Bunsen. The ends and bottoms of porous cells may be thickened for strength. These batteries are expensive at first, owing to the high price of platinum; but the latter does not waste, and is best procured of reasonable stoutness at the outset.

The connections may be soldered; but it is better to have a copper intermediary clamp-piece, and coat it with a protective against the aoid fumes, e.g., Brunswick varnish, or an alcoholic solution of sealing-wax. The Grove battery costs about 3 times as much as a Bunsen of equal power; but its low resistance gives a stronger current for the same size. The connections and conductors must be of stout, soft copper; and the porous cells should have a lip at one corner. The duration of the battery about equals that of the Bunsen, with a smaller consumption of nitric acid.

Fig. 35.