ON THE CONSERVATION OF FORCE. 355 



Each of the four vessels contains nitric acid, in which 

 there is a hollow cylinder of very compact carbon. In 

 the middle of the carbon cylinder is a cylindrical porous 

 vessel of white clay, which contains dilute sulphuric acid ; 

 in this dips a zinc cylinder. Each zinc cylinder is con- 

 nected by a metal ring with the carbon cylinder of the 

 next vessel, the last zinc cylinder n is connected with one 

 platinum plate, and the first carbon cylinder, p, with the 

 other platinum plate of the apparatus for the decomposi- 

 tion of water. 



If now the conducting circuit of this galvanic appa- 

 ratus is completed, and the decomposition of water begins, 

 a chemical process takes place simultaneously in the cells 

 of the voltaic battery. Zinc takes oxygen from the sur- 

 rounding water and undergoes a slow combustion. The 

 product of combustion thereby produced, oxide of zinc, 

 unites further with sulphuric acid, for which it has a 

 powerful affinity, and sulphate of zinc, a saline kind of 

 substance, dissolves in the liquid. The oxygen, moreover, 

 which is withdrawn from it is taken by the water from 

 the nitric acid surrounding the cylinder of carbon, which 

 is very rich in it, and readily gives it up. Thus, in the 

 galvanic battery zinc burns to sulphate of zinc at the cost 

 of the oxygen of nitric acid. 



Thus, while one product of combustion, water, is again 

 separated, a new combustion is taking place that of 

 zinc. While we there reproduce chemical affinity which 

 is capable of work, it is here lost. The electrical current 

 is, as it were, only the carrier which transfers the chemical 

 force of the zinc uniting with oxygen and acid to water 

 in the decomposing cell, and uses it for overcoming the 

 chemical force of hydrogen and oxygen. 



In this case, we can restore work which has been lost, 

 but only by using another force, that of oxidising zinc. 



Here we have overcome chemical forces by chemical 



