238 INDUCTIVE AFFINITY. 



outer cylinder is then nearly filled with a weak solution of com- 

 mon salt, and the inner with a saturated solution of sulphate of 

 copper. The two fluids are prevented from mixing by the 

 plaster diaphragm, and care being taken that they are at the 

 same level in both the cylinders, the circle will afford, on 

 joining the wires, a continuous current for weeks, the chloride of 

 sodium and the sulphate of copper being very slowly decom- 

 posed. After it has been in action for some weeks, chloride of 

 zinc is found in the outer cylinder : and beautiful crystals of 

 metallic copper, frequently mixed with the ruby suboxide 

 (closely resembling the native copper ruby ore), with large 

 crystals of sulphate of soda, are found adhering to the copper 

 plate in the smaller cylinder, especially on that part where it 

 touches the plaster diaphragm. 



The decomposing cell is the counterpart of the battery itself, 

 consisting like it, of two glass cylinders, one within the other, 

 the smaller one c having a bottom of plaster of Paris fixed into 

 it : this smaller tube may be about ^ inch wide and 3 inches in 

 length, and is intended to hold the metallic or other solution to 

 be decomposed, the external tube d, in which the other is im- 

 mersed being filled with a weak solution of common salt. In 

 the latter solution a slip of amalgamated zinc-plate z', soldered 

 to the wire coming from the copper plate c of the battery, is im- 

 mersed ; and a slip of platinum foil p/ 9 connected with the wire 

 from the zinc plate z of the battery, is immersed in the liquor of 

 the smaller tube, being held in its place by a cork, through 

 which its wire passes. The whole arrangement is now obvious- 

 ly a pair of active cells, of which c z' is one metallic element, 

 and z pi the other; and the fluid between z and c divided by the 

 porous plaster diaphragm, one fluid element, and the fluid 

 between z and pi, divided by a porous plaster diaphragm, 

 another fluid element ; although it will be convenient to speak 

 of the last as the cell of decomposition. With a solution of 

 chlorides or nitrates of iron, copper, tin, zinc, bismuth, anti- 

 mony, lead or silver, in the smaller tube, Dr. Bird finds the 

 metals to be reduced upon the surface of the platinum, generally 

 but not invariably in possession of a perfect metallic lustre, 

 always more , or less crystalline and often very beautifully so. 

 The crystals of copper rival in hardness and malleability, the 

 finest specimens of native copper, and those of silver, which are 

 needles, are white and very brilliant. The solution of fluoride 



