M. Dumas on the Law of Substitutions. 179 



Dingle peninsula, from Foylaturrive on the south to Brandon 

 bay on the north, we find that the strata consist of a base of 

 dark blackish-gray clayslate," &c. Now by reversing the 

 points, Mr. Weaver has made the dark gray clayslate to 

 occur on the north side of the peninsula, namely, at Brandon 

 bay, while it really occurs on the south : the misquotation was 

 doubtless unintentional, but as Mr. Weaver's argument was 

 founded on this misconception, it is unnecessary to reply to it. 

 In concluding my observations, I cannot avoid expressing 

 my regret that Mr. Weaver was not present either at the 

 meeting of the British Association at Newcastle, or at the 

 Geological Society of London, when I communicated my 

 views relative to the geological structure of the south of 

 Ireland ; for, viva voce discussion tends more to clear up geo- 

 logical differences than lengthened written descriptions ; and 

 where both parties are in search of truth there is little diffi- 

 culty in attaining it. 



Dublin, July 8, 1840. 



XXVI. Memoir on the Lalo of Substitutions, and the Theory 

 of Chemical Types. By M. DUMAS. 



[Continued from vol. xvi. p. 505, and concluded.] 

 Organic Radicals. 



T^OR some years organic chemistry has so frequently used 

 * what we call organic radicals, that it will appear sin- 

 gular to see, if not their existence, at least the reality of the 

 absolute function which they have been made to play, here put 

 in doubt. 



We know that by the term organic radicals we mean to de- 

 signate certain compound bodies which might fulfil their func- 

 tions in the manner of simple bodies, and which might enter, 

 as they do, and following the same laws, into combination with 

 the various bodies of nature. 



If by organic radicals, bodies analogous to cyanogen, to 

 amidogen, to the oxalic or benzoic radical be intended, there 

 is no doubt that there, in fact, compound bodies perform 

 the function of simple bodies, like those analogous to them 

 in mineral chemistry, the oxide of carbon, sulphuric acid, the 

 binoxide of azote, and nitrous vapour. 



But if by the term organic radicals we must, as M. Berzelius 

 wishes, designate certain invariable compounds which would 

 fulfil the function of the metals, the theory of types, while ad- 

 mitting their concurrence, cannot allow their permanency. 



N2 



