and on Equivalent Volumes, ^ T ♦^M ^IfflL 



such relations that C'^ H* may be compared with O^ H^ and with 

 O^ M^, and by the substitution of nitrogen for hydrogen, with 

 C^ HN, prussic acid, and O^ N^ nitrous oxide (the so-called com- 

 pounds of nitrous oxide with bases are probably O^ MN, corre- 

 sponding to the cyanides, C^MN) ; while theperoxideof hydrogen, 

 O"* H^, corresponds to O'* N^, nitric oxide, and to C'* N^, cyano- 

 gen. This relation has important bearings on the history 

 of the cyanic series, and the nitric derivatives of the hydro- 

 carbons*. 



The formulas of such related species as Gerhardt has desig- 

 nated chemical homologues, differ from each other by nC^ H^ ; if 

 now the relation between C and be what we have supposed, it 

 may be expected that mineral species will exhibit the same rela- 

 tions as those of the carbon series, and the principle of homology 

 be greatly extended in its application. Such is really the case, 

 and the history of mineral species affords many instances of iso- 

 morphous silicates, whose formulas differ by nO^ M^, as the tour- 

 malines, and the silicates of alumina and magnesia, while the 

 latter, with many zeolites, exhibit a similar difference of nO^ H^. 

 The relation is in fact that which exists between neutral and 

 surbasic or hydrated salts. 



05 Laurent has asserted that salts of the same base, with homolo- 

 gous acids of the type (C^ H^) nO"^, may be isomorphous when they 

 differ by 0^ H^, and has pointed out besides, several instances 

 of what he has called hemi-morphism in species thus related, 

 as well as in others differing by nCP. The observations of Pas- 

 teur and Nickles have greatly extended the application of these 

 cases, which assume a new importance in connexion with the 

 views here brought forward, and demand further study f- 



But to return : we have seen that in gases and vapours the 

 specific gravity of a species enables us to lix its equivalent, which 

 is often a multiple by some whole number of that calculated 

 from the results of ultimate analysis. As the equivalents of non- 

 volatile species are generally assumed to be those quantities which 

 sustain the simplest ratio to certain volatile ones, the real equiva- 

 lent weight corresponding to four volumes of vapour, and conse- 

 quently the theoretical vapour- density of such species, is liable to 

 a degree of the same uncertainty as those deduced from ultimate 

 analysis. Having, however, determined the true equivalent of a 



* See page 502 of my Introduction to Organic Chemistry, appended to 

 Silliman's " First Principles of Chemistry/' Philad. 1852 ; and the Amer. 

 Journal for January, 1853, p. 151. 



t See Laurent, Comptes Rendus de VAcad., t. xxvi. p. 353, and p. 257 

 of L. and Gerhardt's Comptes Rendus des Travaux de Chimie for 1848 ; 

 also Pasteur, ibid., p. 165 ; and Nickles, Comptes Rendus des Travaux 

 for 1849, p. 347. .; ,n.^j 



