Chemical Affinity in terms of Electromotive Force. 243 



thus variable, its different values are always simple integral 

 multiples of a common divisor. 



9. Sir William Thomson calculated in 1851 (loc. cit. supra) 

 the value of a% for water on the foot-grain-second electro- 

 magnetic system to be as follows: — 



From data furnished by experiments of Weber . 



Bunsen . 



Casselmann 



Joule 



0-02034 

 0-02011 

 0-01995 

 0-02033 

 0-02021 

 0-01981 

 0-02030 

 0-02002 



Average . . . 0-02013 

 On the C.G.S. system (electromagnetic measure) this ave- 

 rage value becomes 0-0009282. Stas found that 1 part of 

 hydrogen combines with 7*98 of oxygen to form water, whence 

 a =8*98 for water, and consequently 



0-0009282 n . nnmn o«r» 

 %= — g^g — =0*00010336. 



More recent experiments of Kohlrausch (Pogg. Ann. cxlix. 

 p. 170) indicate a perceptibly higher value, viz. 0*00010527 ; 

 for he found that one metre-gramme-second unit of quantity 

 of electricity causes the deposition of 0*11363 gramme of silver, 

 or 1 C.G.S. unit of electricity causes the deposition of 0*011363 

 gramme of metallic silver; i.e. &%= 0*011363, whence 



X = TW? =0 ' 00010527 > 



since Stas found the equivalent of silver to be 107*93. 



In the same paper Kohlrausch gives the following values 

 for the electrochemical equivalent of water deduced from the 

 experiments of Weber, Bunsen, Casselmann, and Joule, allow- 

 ance being made for probable errors in the values assigned to 

 the horizontal component of terrestrial magnetism (the num- 

 bers are given by him in the metre-gramme-second system) : — 



Weber 0*009396 



Casselmann 

 Bunsen . 

 Joule . . 



0*009391 

 0*009624 

 0*009222 



Mean . . . 0*009406 

 On the C.G.S. system this value becomes 0*0009406. whence 

 0*00094 06 

 x ~ ■ 8*98 



= 0*00010474. 



