236 



INDUCTIVE AFFINITY. 



sulphate of copper, and portions of the solid salt are placed 

 upon the circular copper plate, which is perforated like a 

 colander, for the purpose of keeping the solution always in a 

 state of saturation. The internal tube is filled with the same 

 acid mixture without the salt of copper. A tube of porous 

 earthenware, shut at the bottom, may be substituted for the 

 membrane with great convenience, but Mr. Daniell believes with 

 some little loss of power. A section of the upper part of one 

 of these cells is here represented, a b c dis (Fig. 24) the external 

 copper cylinder ; e f g h, the internal 

 cylinder of earthenware, and / m the rod 

 of amalgamated zinc. Upon a ledge c d, 

 within an inch or two of the top of the 

 cylinder, rests the cylindrical colander i k, 

 which contains the copper salt, and both 

 the sides and bottom of which are perfo- 

 rated with holes. A number of such cells 

 may be connected into a compound cir- 

 cuit, with wires soldered to the copper 

 cylinders, and fastened to the zinc by 

 clamps and screws as shewn below. 

 Fig. 25. (Darnell's Introduction to Che- 

 mical Philosophy, page 440.) 

 ;p JG 25. I n this instrument 



the sulphate of zinc, 

 formed by the solu- 

 tion of the zinc rod, 

 is retained in the 

 z membranous bag or 

 stoneware cylinder, 

 and prevented from 

 diffusing to the cop- 

 per surface ; while 

 the hydrogen, in- 

 stead of being evolv- 

 ed as gas on the sur- 

 face of the latter metal, decomposes the oxide of copper of 

 the salt there, and occasions a deposition of metallic copper 

 on the copper plate. Such a circle will not vary in its 

 action for hours * together, which makes, it invaluable m 

 the investigation of voltaic laws. It owes its superiority prin- 





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