214 HELMHOLT2 



hydrogen which has here been liberated from the water by 

 the electrical current has regained the capacity of producing 

 large quantities of heat by a fresh combination with oxygen ; 

 its affinity for oxygen has regained for it its capacity for 

 work. 



We here become acquainted with a new source of work, 

 the electric current which decomposes water. This current 

 is itself produced by a galvanic battery, FIG. 101. 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 connected 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 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 surround- 

 ing 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 The oxygen, moreover, which is withdrawn from it 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 capa- 

 ble 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 decom- 

 posing 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. 



