Propionic and Caproic Acids, 205 



Propylicacid . . CWOq 



Butyric acid . . . C 4 h 7 



0, 



each term containing C h 2 more than the preceding. 



Now Dr. Wrightson assumed that if this theory were correct, 

 other acids ought to exist, lying between these in their compo- 

 sition ; whereas it is evident that, if such bodies existed, we could 

 not consistently with any theory represent them by fractional 

 formulae such as 



C§h 2 n 

 h u > 

 but must double the formulae of the original series to make room 

 for the insertion of these new terms with entire numbers ; so 

 that the existence of these putative acids would have been a deci- 

 sive argument against the correctness of the othyle theory. This 

 theory ought hardly to be blamed for the non-existence of two 

 alcohol-radicals in an acid, where it denies the existence of even 

 one. 



As regards the other theory which Dr. Wrightson considers 

 in connexion with the above reaction, I must frankly state, that, 

 although the existence of the imaginary acids might be conceived 

 consistently with it, I do not consider the non-existence of those 

 acids as affording any evidence against it. If acetic acid con- 

 tained two atoms of methyle (C h 3 ), and propylic acid two atoms 

 of aethyle (C 2 h 5 ), it would be quite conceivable that an interme- 

 diate acid might exist containing one atom of methyle and one 

 of sethyle ; but I could not, even according to Kolbe's theory, 

 conceive it formed from the mixture of two cyanides. Kolbe's 

 original theory, by which acetic acid was represented as oxalic 

 acid and methyle, has the merit of accounting in a very satisfac- 

 tory manner for several important reactions, and has undoubtedly 

 been of great service to our progress in the subject; but the 

 recent modification with which we have been favoured by that 

 distinguished chemist is so complicated, and introduces such 

 unintelligible symbolical distinctions, that it seems likely to serve 

 chiefly as an extinguisher of the original theory. 



As Kolbe's and Frankland's beautiful reaction of the cyanides 

 with potash is the process most usually adopted for the prepara- 

 tion of propylic or caproic acids, I may be permitted to describe 

 a slight modification in the method employed for the formation 

 of cyanide of sethyle or amyle, by which large quantities of these 

 substances may be prepared with far less trouble and annoyance 

 for the purpose of that reaction. Everybody who has distilled 

 sulphovinate of potash with cyanide of potassium must be aware, 



