LECTURE XII.] HISTORY OF CHEMISTRY. 225 



as hyposulphuric (dithionic) acid coupled with different 

 radicals, and writes their formulae : 



C 2 C1 3 + S 2 O 5 + HO Chlorkohlenunterschwefelsaure. 



C 2 HC1., + S 2 O 5 + HO Chlorformylunterschwefelsaure. 



C 2 H 2 C1 + S.,O 5 + HO Chlorelaylunterschwefelsaure. 



C 2 H 8 + S 2 O 5 + HO Methylunterschwefelsaure. 



Kolbe succeeds in effecting the synthesis of trichloracetic 

 acid in a similar manner, that is, by treating chloride of carbon 

 with chlorine in sunlight, in presence of water. In this he 

 finds a ground for the assumption by Berzelius of the presence 

 of chloride of carbon in trichloracetic acid, and thereby secures 

 an important footing for Berzelius' whole mode of regarding 

 these compounds. At the same time the analogy of the sub- 

 stance discovered by Dumas, with the compounds containing 

 sulphur, prepared by Kolbe, is now furnished, since trichlor- 

 acetic acid was written, after the style of Berzelius, C 2 C1 3 + C 2 O 3 

 4-HO. It was thus a conjugated oxalic acid, whilst the others 

 were conjugated hyposulphuric acids. 



Kolbe admits, as Berzelius had done previously, the replace- 

 ment of hydrogen by chlorine in the copula. That a substitu- 

 tion of this kind should be possible without essential alteration 

 of the properties, depended upon the assumption that the 

 nature of the copula exercised only a subordinate influence 

 upon the character of the compound. Kolbe, no doubt, per- 

 ceives (what Berzelius never admitted) that he thereby adopts 

 an essential point in the theory of substitution. 



It appears to me necessary to state distinctly that Kolbe, 

 and also Frankland (who, at that time, agreed completely with 

 Kolbe's views), adopted the conception of a radical in its 

 earlier sense. They believe in the existence in compounds of 

 certain atomic groups, and are, therefore, far from admitting, 

 with Gerhardt, that different radicals may be assumed to be 

 present in a substance. Both Kolbe and Frankland attack the 

 problem of ascertaining the constitution of compounds, and, 

 by doing so, they essentially distinguish themselves from 



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