xvn MOLECULAR ARCHITECTURE 407 



iodine, of oxygen, etc., for each atom of hydrogen which 

 it loses, it gains an atom of chlorine, of bromine or of 

 iodine, or half an atom of oxygen ; 



2. When the hydrogenated compound contains oxygen, 

 the same rule applies without modification ; 



3. When the hydrogenated compound contains water, 

 this loses its hydrogen without replacement, and hereafter, 

 if a further quantity of hydrogen is removed, it is replaced 

 as in the preceding cases" (Treatise on Chemistry ', 1835, V. 

 99). 



The following examples of simple substitution of chlorine 

 for hydrogen are given in his Memoir (loc. cit. pp. 549-556) 

 and quoted again in his Treatise (loc. cit. pp. 99-102). 



(a) Gay-Lussac, in 1815, (Ann.de Chimie, 1815, 95, 210) 

 had shown that hydrogen cyanide, in passing into cyanogen 

 chloride " loses one volume of hydrogen and gains exactly 

 one volume of chlorine." 



HCN + C1 2 = C1CN + HC1. 



(b) Wohler and Liebig, in 1832 (see above p. 400), had 

 shown that oil of bitter almonds "treated with chlorine, 

 loses two volumes of hydrogen and gains precisely two 

 volumes of chlorine." 



C 7 H 6 + C1 2 = C 7 H 5 OC1 + HC1. 1 



(c) Faraday, in his experiments on the chlorination of 

 Dutch liquid^(ethylene chloride) (Phil. Trans^ 1821, 47-74), 

 had found that " chlorine, acting on it in sunlight, produces 

 a chloride of carbon, absolutely free from hydrogen." The 

 composition of this solid perchloride of carbon can be pre- 

 dicted by the law of substitution and agrees exactly with 

 Faraday's analysis. 



C 2 H 4 C1 2 + 4C1 2 = C 2 C1 6 + 4HC1. 



Removal of hydrogen without replacement. The re- 

 servation in the third law of substitution was introduced to 



1 These formulae were doubled: hence the "two volumes" of 

 hydrogen and chlorine. 



