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



the case may be, of hydrogen. Nothing whatever is signified 

 with respect to the proximate constituents of felspar. 



But how may we consider the elements in felspar to be united 

 to proximate constituents ? and how again may these be supposed 

 to be combined among themselves ? The cases possible are 

 numerous. 



Felspar may contain the tetrabasic orthosilicic acid corre- 

 sponding to orthocarbonic acid, of which the hydrate is consti- 



(OIH 



AT] 



tuted according to the formula Si< ^ >tj- Or it may contain 



LoJh 



the dibasic silicic acid (SiO)"< ^ > „, corresponding to ordinary 

 carbonic acid. In either case felspar would be an acid silicate : 



01 



^ I + 2 SiO 2 , acid silicate of the ortho-acid. 

 K 



• sio rcn 



SO I O ' + Si0 2 , acid silicate of the dibasic acid. 



lO J K 



The neutral silicate corresponding to the latter compound 

 would possess a constitution analogous to dehydrated alum. 



SiO CO 1 



SiO I O I > neu ^ ra ^ aluminium potassium silicate. 

 lO K 



so 2 rcn 



S0 2 1 O I > dehydrated alum. 

 lO K 



But felspar may be represented as a neutral salt when we 

 assume in it the presence of a tetrabasic silicic acid radical, (Si 8 O 4 ), 



Felspar = (Si 3 O 4 ) j ° f A1 . 

 lo K 



Whether the supposition of this tetrabasic silicic acid, which 

 in some degree corresponds to tetrabasic pyrophosphoric acid, 

 (P 2 O 3 ) O 4 H 4 , is permissible cannot here be discussed. 



There is still another method of representing felspar as a neu- 



