474 PRINCIPLES OF CHEMISTRY 



CH 3 takes the place of the chlorine. In this, or in a similar manner, 

 CH 3 -CH 3 , or C 2 H 6 is obtained fromOH 3 Cl andC 6 H 5 -CH 3 from 6 H 6 . 

 The products of metalepsis also often react on ammonia, forming hydro- 

 chloric acid (and thence NH 4 C1) and an amide ; that is, the product of 

 metalepsis, with the ammonia radicle NH 2 , &c. in the place of chlorine. 

 Thus by means of metalepsical substitution methods were found in 

 chemistry for an artificial and general means of the formation of com- 

 plex carbon compounds from more simple compounds which are often 

 totally incapable of direct reaction. Besides which, this key opened 

 the doors of that secret edifice of complex organic compounds into 

 which man had up to then feared to enter, supposing the hydrocarbon 

 elements to be united only under the influence of those mystic forces 

 acting in organisms. 26 



It is not only hydrocarbons which are subject to metalepsis. 

 Certain other hydrogen compounds, under the action of chlorine, also 

 give corresponding chlorine derivatives in exactly the same manner ; 

 for instance, ammonia, caustic potash, caustic lime, and a whole series 

 of alkaline substances. 27 In fact, just as the hydrogen in marsh gas 

 can be replaced by chlorine and form methyl chloride, so the hydrogen 

 in caustic potash, KHO, ammonia, NH 3 , and calcium hydroxide, 



* With the predominance of the representation of compound radicles (this doctrine 

 dates from Lavoisier and Gay-Lussac) in organic chemistry, it was a very important 

 moment in its history when it became possible to gain an insight into the structure of 

 the xadicles themselves. It was clear, for instance, that ethyl, C 2 H 5 , or the radicle of 

 common alcohol, C 2 H 5 -OH, passes, without changing, into a number of ethyl 'derivatives, 

 but its relation to the still simpler hydrocarbons was not clear, and occupied the attention 

 of science in the ' forties ' and ' fifties.' Having obtained ethyl hydride, C 2 H 5 H = C 2 H 6 , it 

 v?as looked on as containing the same ethyl, just as methyl hydride, CH^^CH^H., was 

 considered as existing in methane. Having obtained free methyl, CH 3 CH5=C 2 He, from 

 it, it was considered as a derivative of methyl alcohol, CH OH, and as only isomeric with 

 ethyl hydride. By means of the products of metalepsis it was proved that this is not a 

 case of isomerism but of strict identity, and it therefore became clear that ethyl is 

 methylated methyl, C 2 H 5 = CH 2 CH 3 . In its time a still greater impetus was given by 

 the study of the reactions of monochloracetic acid, CH 2 C1'COOH, or CO(CH 2 C1)(OH). 

 It appeared that metalepsical chlorine, like the chlorine of chloranhydrides for instance, 

 of methyl chloride, CH 3 C1, or ethyl chloride, C._,H 5 C1 is capable of substitution ; for 

 example, glycollic acid, CIL^OHXCOjH), or CO(CH S -OH)(OH), was obtained from it, and 

 it appeared that the OH in the group CH 2 (OH) reacted like that in alcohols, and it 

 became clear, therefore, that it was necessary to examine the radicles themselves by 

 analysing them from the point of view of the bonds connecting the constituent atoms. 

 Whence arose the present doctrine of the Structure of the carbon compounds. (Se* 

 Chapter VIIL, Note 42.) 



n By including many instances of the action of chlorine under metalepsis we not 

 only explain the indirect formation of CC1 4 , NC1 S , and C1 2 by one method, but we also 

 arrive at the foct that the reactions of the metalepsis of the hydrocarbons lose that 

 exclusiveness which was often ascribed to them Also by subjecting the- chemical vepre 

 sentations to the law of substitution we may foretell metalepsis as a particular case of a 

 general law. 



