M. H. Kolbe on the Province of Mineral Chemistry. 349 



The lively interest excited by the discovery of isomorphism is 

 now succeeded by an ardent zeal in searching out the origin of 

 the numberless instances of isomerism in organic compounds. 

 Hitherto isomeric compounds have scarcely been observed in 

 inorganic chemistry, much less in mineral chemistry. This may 

 be owing partly to the simpler constitution of inorganic com- 

 pounds, in consequence of which isomerism is not possible to 

 the same extent as in organic chemistry, and partly to the fact 

 that until now we have altogether neglected to study inorganic 

 substances with respect to their chemical constitution. 



The truth of the latter assertion becomes at once evident when 

 we attempt to frame a reply to any inquiry respecting the consti- 

 tution of the naturally occurring silicates — felspar for example — 

 such as what are the proximate constituents of these compounds, 

 and what are their several functions. Let us see the extent of 

 our knowledge in this direction. 



Berzelius regarded felspar as built up according to the formula 

 Al 2 3 3Si0 3 + KOSi0 3 (old atomic weights), viewing it as a 

 double salt of neutral silicate of alumina and silicate of potash, 

 analogous to dehydrated alum. 



Such a comparison is no longer applicable, since as the atomic 

 weight of oxygen is now doubled, and silicon is regarded as a 

 tetratomic element, the molecule of felspar contains three atoms 

 of silicon, whilst that of alum possesses only two of sulphur. 



Felspar .... Al, K, Si 3 , O 8 . 

 Alum (dehydrated). Al, K, S 2 , O 8 . 



Afterwards, when Gerhardt* declared that all investigations 

 designed to elucidate chemical constitution could only end in 

 disappointment, thinking that he had rendered such investiga- 

 tions superfluous by his theory of types (that is, by the mere 

 mechanical use of a soulless schematism), felspar became water 

 in which the atoms of hydrogen were substituted by silicon, 

 aluminium, and potassium, and its constitution was expressed 

 by the formula 



sin sin 



Al 2 [O 16 or Al '>o 8 . 

 K 2 J K J 



These expressions possess nothing beyond the signification of a 

 sum in addition over the purely empirical formulae Si 6 Al 2 K 2 O 16 , 

 or Si 3 Al K O 8 ; that is to say, they simply indicate that the sum 

 of the affinities of the atoms of silicon, aluminium, and potassium 

 present in felspar is equivalent to that of 32 or of 16 atoms, as 



* Comptes Rendus des travaux de Chimie, par Laurent et Gerhardt. 

 1851, p. 65. 



