BATTERIES. 69 



zinc D coiled in a spiral shape and suspended from the ebonite 

 cover Gr. The wires C and F are the electrodes, C being attached 

 to the boss A, and F to a terminal which communicates with 

 the positive electrode. 



The external cell V contains oxide of copper B on the top 

 of which is poured a depolarising solution of caustic potash of 

 30 or 40 per 100. 



The cover is hermetically sealed by means of three flanges 

 screwed down by as many nuts. 



When the circuit is closed the water is decomposed, the 

 oxygen forming with the zinc oxide of zinc which combines 

 with the potash to form an excessively soluble zincate of 

 potash; the hydrogen reduces the oxide of copper to a 

 metallic state. 



In open circuit the materials are not attacked, therefore 

 there is no reaction and consequently no expenditure. 



The electromotive force varies between 8 and 9 volt, 

 and it remains perfectly constant for a long time. 



SMEE CELL. The Smee cell is simple and economical, but 

 its depolarisation is less complete than that of cells with two 

 liquids. It is composed of a vessel containing dilute acid, a 

 positive electrode of amalgamated zinc, and a negative electrode 

 of platinised silver ; the bubbles of hydrogen escaping more 

 freely on such a deposited surface of grey pulverulent rough 

 platinum than on a polished metallic surface. 



In order to increase the constancy of this cell, a small 

 quantity of platinum chloride is often added to the liquid. 

 Some makers, instead of platinised silver plates, use copper 

 plates, on which are successively deposited a layer of galvanic 

 copper, a layer of granulous silver, and a layer of pulverulent 

 platinum. 



The Smee cell is extensively used in England and in 

 America in small nickeling and electrotyping works. It is par- 

 ticularly applicable for operations in which the current must be 

 energetic at the beginning and may be weaker afterwards. 



In France it has been almost forgotten, notwithstanding 

 the economy which it obtains over the generality of other 

 systems. 



