16 Mr. T. S. Hunt on the Theory 



and BiEt 3 , are by Kolbe assimilated to the oxides of ZnO, PbO 2 , 

 and BiO 3 . 



Ad. Wurtz, in the Repertoire de Chimie Pure for October 

 1860, has given an analysis of Kolbe's memoir (to which, not 

 having the original before me, I am indebted for the preceding 

 sketch), and follows it by a judicious criticism. While Kolbe 

 adopts as types a number of mineral species, including the 

 oxides of carbon, of sulphur and the metals, Wurtz would main- 

 tain but three, hydrogen (H 2 ), water (H 2 O 2 ), and ammonia 

 (N H 3 ) ; and these three types, as he endeavoured to show in 

 1855, represent different degrees of condensation of matter. 

 The molecule of hydrogen, H 2 (M 2 ), corresponding to four 

 volumes, combines with two volumes of oxygen (0 2 ) to form 

 four volumes of water, and may thus be regarded as condensed 

 to one-half in its union with oxygen, and derived from a double 

 molecule, M 2 M 2 . In like manner four volumes of ammonia 

 contain two volumes of nitrogen and six of hydrogen, which, 

 being reduced to one-third, correspond to a triple molecule, 

 M 3 M 3 , so that these three types and their multiples are redu- 

 cible to that of hydrogen more or less condensed*. 



As regards the rejection of water as a type of organic com- 

 pounds, and the substitution of carbonic acid, founded upon the 

 consideration that these in nature are derived from C 2 4 , Wurtz 

 has well remarked that water, as the source of hydrogen, is 

 equally essential to their formation, and indeed that the carbonic 

 anhydride, C 2 O 4 , like all other anhydrous acids, may be regarded 

 as a simple derivative of the water type. Having then adopted 

 the notion of referring a great variety of bodies to a mineral 

 species of simple constitution, water is to be preferred to carbonic 

 anhydride, — first, because we can compare with it many mineral 

 compounds which can with difficulty be compared with carbonic 

 acid; and secondly, because, the two atoms of water being 

 replaceable singly, the mode of derivation of a great number 

 of compounds (acids, alcohols, ethers, &c.) is much more sim- 

 ple and natural than from carbonic acid. As Wurtz happily 

 remarks, Kolbe has so fully adopted the theory of types, that he 

 wishes to multiply them, and even admits condensed types, which 

 are, however, molecules of carbonic acid, and not of water ; " he 

 combats the types of Gerhardt, and at the same time counterfeits 

 them." 



Thus far we are in accordance with M. Wurtz, who has shown 

 himself one of the ablest and most intelligent expounders of 

 this doctrine of molecular types, as above defined, now almost 

 universally adopted by chemists. He writes, " To my mind 

 this idea of referring to water, taken as a type, a very great 

 * Wurtz, Ann. de Chim. et de Phys. [3.] vol. xliv. p. 304. 



