242 ENERGY OF CURRENTS. 



molecules of water are not invariably united to the corresponding 

 molecules of oxygen ; but, carried along in an incessant eddying, they 

 may quit the first molecule of oxygen, to become combined with 

 adjacent ones ; and thus by a series of successive interchanges they 

 may be carried to distances which are infinitely great in comparison 

 with their radius of activity. In the ordinary condition, the directions 

 of these motions are perfectly irregular ; the passage of electricity 

 imparts to them a systematic tendency, owing to which the molecules 

 of hydrogen moving with the current are impelled towards the 

 negative electrode ; those of oxygen, on the contrary, going in the 

 opposite direction move towards the positive electrode. 



250. FARADAY'S FIRST LAW. The first experiments on the 

 decomposition of water by electricity appear to have been due to 

 Troostwyk and Diemann in 1795. They employed the spark of the 

 battery passing between two gold or platinum wires. The experiment 

 was repeated in 1800 by Carlisle and Nicholson by means of the 

 current of the voltaic pile. In working with sparks it is advantageous 

 to use what are called Wollastoris electrodes, which consist of a 

 platinum wire passed into a glass tube in such a way that only the 

 mere section of the wire is in contact with the liquid. Wollaston, 

 Faraday, Armstrong, have shown that the effect of the spark is 

 identical with that of the battery. Whatever be the origin of the 

 electricity, the quantity of water decomposed is proportional to the 

 quantity of electricity which passes. 



This law, which was enunciated by Faraday, has been more 

 particularly verified by the electromagnetic measurement of currents ; 

 but the direct determination of the quantity of electricity by elec- 

 trostatic methods also allows of a very exact demonstration. In 

 some recent experiments Dr. Warren De La Rue discharged a 

 condenser which had been charged to potentials i, 2, 3, through 

 water, and verified the exact proportionality between the quantity of 

 electricity and the quantity of water decomposed. This propor- 

 tionality enables us to regard electrolytes as measurers of electricity ; 

 the term voltameter is applied to an apparatus arranged so that the 

 gases arising from the decomposition of water may be collected. 



251. The work of chemical decomposition being proportional to 

 the strength of the current, it follows, from the remark made above, 

 that there must be somewhere in the voltameter a sudden fall of 

 potential H, independent of the strength. The energy made avail- 

 able by the fall of the current at this point, is used in decomposing 

 the water, and may be calculated in absolute value. 



Let M be the quantity of electricity which has passed through 



