Prof. Thomson on the Mechanical Theory of Electrolysis, 437 



were subject to no frictional or other resistance ; and that if, by re- 

 sisting forces, it were kept steadily revolving at the rate of w turns 

 per second, it would, in overcoming those forces, be performing 



-— — - of the whole work due to the consumption of zinc and 

 79803 



deposition of copper in the battery. 



13. If the electro -chemical apparatus mentioned in § 4 be a 

 vessel of pure water with two plates of platinum immersed in it, 

 we may consider a grain of hydrogen electrolysed as the unit for 

 measuring the chemical action which takes place. Now Mr, 

 Joule finds that, in the electrolysis of one grain of hydrogen 

 from water acidulated with sulphuric acid, as much heat is ab- 

 sorbed as would raise the temperature of 33553 grains of water 

 from 0° to 1°. Hence 6 must be less than 33553 by the quan- 

 tity of heat evolved when as much pure water as contains one 

 grain of hydrogen is mixed with acidulated water, such as that 

 used by Mr. Joule ; but, without appreciable error on this ac- 

 count, we may take 



6'=33553. 



I have found also, from results of experiments on the electro- 

 lysis of water made by Mr. Joule at Manchester in 1845, that 

 the electro-chemical equivalent of hydrogen is "002201. IJsing 

 this value for e, and the values indicated above for 6 and J, we 

 have by (12), 



1=3305400 



for the electro-motive force, in absolute measure, required for the 

 decomposition of water. This exceeds the electro-motive force 

 of a single cell of DanielFs battery, found above, in the ratio 

 of 1*318 to 1. Hence at least two cells of DanielPs battery are 

 required for the electrolysis of water; but fourteen cells of 

 DanielFs battery connected in one circuit with ten electrolytic 

 vessels of water with platinum electrodes would be sufficient to 

 efi^ect gaseous decomposition in each vessel. 



14. In the Bakerian Lecture of 1832, *^*^0n Terrestrial Mag- 

 neto-electric Induction," Faraday, after describing some experi- 

 ments he had made at Waterloo Bridge, without however arriving 

 at any positive results, to test the existence of an inductive efiect 

 of the terrestrial magnetic force upon the flowing water of the 

 Thames, brought forward some very remarkable speculations 

 regarding the possible efibcts of magneto-electric induction upon 

 large masses in motion relatively to the earth, or upon the earth 

 itself in motion with reference to surrounding space. The pre- 

 ceding investigations enable us to compare the electro-motive 

 forces in such cases with electro-motive forces the effects of 

 which are familiarly known to us, and so to form some estimate. 



