Jbr exciting Voltaic Electricity, 149 



4 to 1, and their equivalents nearly as 3 to 1, taking only 

 half of the atomic number of the former, because blue vitriol 

 is a bisulphate; so that for equivalents of sulphuric acid the 

 price is nearly as 12 to 1, but the former gives off' six times as 

 much gas as the latter, so that for equal electrolyzing power 

 the price would be nearly as 2 to 1 ; but then, to get the same 

 electrolyzing power requires six times the equivalent propor- 

 tion of acid, by which of course six times as much zinc must 

 be destroyed, which will add materially to the expense; in 

 other words, comparatively diminish that incurred by the use 

 of the sulphate of copper. When nitre is mixed with the sul- 

 phate the electrolytic action is as 8 to 1, so that the slight 

 additional expense of the nitre, without adding to the expen- 

 diture of zinc, is more than counterbalanced by the increase 

 of power. Though sea salt does not increase the electrolytic 

 action of the sulphate so much as nitre does, yet considering its 

 cheapness compared with it, it is the most ceconomical of the 

 substances tried. Thus 490 of oil of vitriol yielded 40 of gas, 

 and 1250 of sulphate of copper +600 sea salt gave 310, con- 

 sequently 490 with the requisite proportion of salt would 

 yield 120, or three times as much as the oil of vitriol would 

 do ; so that the expense of the fluids would be about 4 to 3. 

 But as eight equivalents of acid are required to yield the 310 

 of gas, and consequently eight equivalents of zinc consumed, 

 Ul other words, as only Jth of the quantity of zinc is de- 

 stroyed, for getting the same electrolytic action when the sa- 

 line solution is used, though the price of the fluids is as 4 to 3, 

 the expense would in all, even with the addition of the salt, be 

 only about half of that incurred by using the oil of vitriol. 



The above remarks regarding the comparative expense of 

 the materials mentioned, it must be borne in mind, apply to 

 the electrolytic power when the troughs which are in common 

 use are employed. It is different when the trough recom- 

 mended by Faraday (Phil. Magazine, February 1836, Third 

 Series, vol. viii., p. 114,) is used. According to him, when 

 acting with nitrosulphuric acid it decomposed one equivalent 

 of water, at the expense of 2*21 equivalents of zinc, in each 

 plate, and of course of a corresponding quantity of acid ; 

 whereas were the whole of the electricity conveyed through 

 the electrolyte, 2*21 of water ought to have been decom- 

 posed ; so that there was a loss of about 55 per cent, of the 

 electrolytic agent. It has been already mentioned that with 

 sulphate of copper and nitre, while the quantity of water which 

 should have been decomposed would have yielded 15*75 cubic 

 inches of hydrogen, there were given off" only 13*2, and with 

 the mixture of sulphate and sea salt, only 1 2*6 cubic inches, 



