352 EXPERIMENTAL INVESTIGATIONS. 



dilute sulphuric acid only this latter, to overcome a given 

 resistance, say to decompose an equivalent of water, requires 

 a series of at least three cells, while only one of the nitric acid 

 battery is requisite. Hence we have in the first, three equi- 

 valents of zinc and three of sulphuric acid consumed ; in the 

 second, one of zinc, one of sulphuric acid, and one-third of 

 nitric acid; for nitric acid having five equivalents of oxygen, 

 three of which are actually available, does three units of work. 

 The calculation then becomes as given in the annexed table : 



Chemical equivalent of zinc, 32. 



Chemical equivalent of nitric acid, 54. 



54-3=18. 



32 : 181:45 : 25-3. 



45 Ibs. of zinc at $d.= iis. $d. 



25*3 Ibs. of real (i.e. 5o - 6 of commercial) nitric acid, at 6d. 

 = i/. sj. ftd. 



us. 3</. + i/. $s. 7^</.= i/. i6s. ioj</., the expense of one 

 horse-power for twenty-four hours. 



In this the small expense of the sulphuric acid and minute 

 waste of mercury are thrown out of the equation, as more than 

 balanced by the salts formed during the action of the battery. 

 It is evident from this that the expense of electro-magnetic 

 machines far exceeds that of steam ; indeed, it could hardly 

 be expected to be otherwise, as with the one we use for fuel 

 manufactured materials, in the production of which coals, 

 labour, &c., have been expended ; in the other, coals and 

 water are used directly. This is rather discouraging ; but at 

 the same time we must recollect that in magnetic motion 

 nothing is wasted ; when the machine stops the consumption 

 stops also ; and Mr. Grove thinks that we should not so much 

 direct our endeavours to rival steam, as to find out methods 

 of application where steam cannot be applied. The telegraph 

 is one of these, and probably some others will be found ; at 

 all events, the idea that so much ingenuity, labour, and per- 

 severance should have been applied, and should have marched 

 with rapid strides in vain, is contradicted by the whole 

 history of science ; and though it may not be very easy to 

 point out the exact where, when, and how of its success, still, 



