This battery consists of zinc and copper plates united in pairs, and fitting into grooves in a wooden trough, the space left between the pairs of plates accommodating the excitant. This latter is dilute sulphuric acid with a slight addition of nitric. The battery is used as a compound for medical and telegraphic purposes, but it is not very convenient.

Daniell's

The Daniell battery consists of a copper cylinder containing another of porous earthenware, in which is placed a zinc rod; this latter forms the positive and the copper the negative element. ' The battery requires 2 excitants - a saturated solution of copper sulphate in the copper cylinder, and dilute sulphuric acid (1 volume oil of vitriol to 7 of water) in the porous cell. The walls of the latter keep the solutions separate, while allowing the electric current to pass through. The cathode and anode are formed by attaching binding screws to the zinc rod and copper cylinder. The battery requires no frame, is effective in use, constant, and gives a current of fair intensity. (Dyer.)

To construct a home-made Daniell cell, select a small round earthenware jar, such as is used for keeping preserves, and having lined the bottom with guttapercha, or some suitable cement, to the depth of 1/4 in., fix upright in this a rod of zinc, of equal height with the jar, to which a length of copper wire has been attached by passing it through a hole drilled in the upper part of the zinc rod, or by soldering. Make a cylinder of pipeclay, or other porous clay, larger than the zinc rod, and having dried it, make it hot in the fire by degrees, till it attains a red heat. Let this cylinder cool gently, and when cold, place it in the jar round the central rod, encircling it at a little distance. By moderately heating the end of the cylinder, it will, when placed on the guttapercha, make a groove which will fix the tube, and prevent infiltration of the fluids. Line the inside of the jar with a plate of thin copper, bent into a cylindrical form, and having a few holes punched in it, through which may be threaded the extremity of another length of copper wire. On the top of this cylinder place a flat ring of copper pierced with holes, and nearly, but not quite, touching the porous cylinder. This forms the battery.

To charge it, a saturated solution of copper sulphate is poured between the copper and the clay tube, and some crystals of the same salt are placed upon the perforated ring so as just to be in contact with the solution. The zinc compartment is then filled with a solution of zinc sulphate, sal-ammoniac, or common salt. (Electrician.)