ON THE STATE OP ORGANIC CHEMISTRY. 17 



which contain the same quantity of hydrogen, there is a common difference 

 of C 3 . 



It can only be decided by the progress of discovery which of these modes 

 of classifying chemical groups is the most accurate expression of their 

 mutual relations. 



If from the point of view which we have now reached, we look back at 

 Gerhardt's system of types of decomposition, we see that almost all the ad- 

 vances which have been made in theoretical chemistry, since that system 

 was proposed, are included in the development and systematizing of the idea 

 of polyatomic radicles, an idea, which was to some extent adopted by Ger- 

 hardt, but which it could easily be shown was not followed out by him with 

 perfect consistency. 



In conclusion of our account of the recent advances of organic chemistry, 

 we may enumerate some of the most important reactions, or methods of 

 transformation, which, within the last four or five years, have been shown to 

 be applicable to the compounds of various groups, or which, from their nature, 

 appear to be capable of such a general application. They may be divided 

 for this purpose into — 



(I.) Heterologous transformations, or transformations in which there is a 

 change of chemical functions, but in which the new substances produced 

 belong to the same chemical group as the substances from which they are 

 formed. (II.) Homologous transformations, or transformations in which 

 there is a passage from one group to another homologous with it. (Ill-) 

 Isologous transformations, or the passage from one group to another which is 

 isologous with it. 



I. Heterologous transformations. Several transformations of this kind have 

 been already referred to as enabling us to pass from monatomic to polyatomic 

 compounds, and vice versa. We may mention further — 



(A) The conversion of ethylene and its homologues into the correspond- 

 ing monatomic alcohols by combining them with acids, and the subsequent 

 decomposition by water, or by alkaline hydrates, of the compounds thus 

 formed* ; e.g. — 



C'IP + H'SO 1 = C 2 H 6 S0 4 

 Ethylene. Ethylsulphuric acid. 



C'H 6 + HC1 = C 3 H 7 C1 



Propylene. Chloride of trityl. 



(B) The formation of nitrogen compounds containing zinc (as zinc-amide, 

 nitride of zinc, phenyl-zinc-amide, &c.) by the action of zinc-ethyl on the 

 derivatives of ammonia f ; e. g. — 



C 2 H 5 Zn + C 6 H 7 N = C 2 H 6 + C 6 H°ZnN 



Zinc-ethyl. Phenylamine. Hydride of Phenyl-zinc- 



ethyl. amide. 



(C) The substitution of ethyl and methyl for chlorine in combination 

 with phosphorus and arsenic by the action of zinc-ethyl or zinc-methyl on 

 terchloride of phosphorus or of arsenic £ ; e. g. — 



3C 2 H 3 Zn + Cl 3 P = 3Cl 2 Zn + (C 2 H 5 ) 3 P. 

 Zinc-ethyl. Teretl.yl- 



phosphine. 



(D) The similar substitution of ethyl and methyl for chlorine or iodine 



* Berthelot, Ann. Chim. Phys. [3] xliii. 385; li. 81. 

 t Frankland, Proc. Roy. Soc. viii. 502. 



X Hofinann and Cahours, Chem. Soc. Quart. Journ. xi. 56 ; Ann. Chem. Pharm. civ. 1 ; 

 Ann. Chim. Phys. [3] li. 5. 



1859. c 



