ON THE CONSERVATION OF FORCE. 311 



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

 other platinum plate of the apparatus for the decomposition of 

 water. 



If now the conducting circuit of this galvanic apparatus 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 surrounding 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 moreover, which is withdrawn from it is taken by the water 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 forces, 

 through the instrumentality of the electrical current. But we 

 can attain the same object by mechanical forces, if we produce 

 the electrical current by a magneto-electrical machine, Fig. 50. 

 If we turn the handle, the anker R R 1 , on which is coiled 

 copper- wire, rotates in front of the poles of the horse -shoe 

 magnet, and in these coils electrical currents are produced, which 

 can be led from the points a and 6. If the ends of these wires 

 are connected with the apparatus for decomposing water, we 

 obtain hydrogen and oxygen, though in far smaller quantity than 

 by the aid of the battery which we used before. But this pro- 



