M. H. Kolbe on the Province of Mineral Chemistry. 351 



tral salt, when we assume therein a similar method of combina- 

 tion to proximate constituents as that which is supposed to occur 

 in the case of potassium dichromate. 



Thus, when two atoms of the divalent radical of chromic acid, 

 CrO 2 , are so combined with an atom of oxygen that its affinities 

 are divided between them, we obtain the divalent acid radical 



ic'Cit f ® ) °f tne P otass i um dichromate, \^™ fO) r\ xr' 



Now, if we assume that two atoms of the divalent silicic acid ra- 

 dical SiO are united in a similar manner to an atom of oxygen, 

 we have a new dibasic silicic acid, of which the neutral potash- 

 salt is built up according to the formula ( ~* VQ \ ~ ' ^*. If 



we further suppose this salt to be combined with the neutral 

 potash-salt of normal dibasic silicic acid, as indicated by the for- 



(sio)°)(ol 1 



mula ^ -J ' \ n \ Tr , and substitute an atom of trivalent 

 (SiO) [gjf 



aluminium for three atoms of potassium, we obtain felspar pos- 

 sessing the following; constitution : — 



Now to which of these four isomeric compounds, of which 

 the number might doubtless be increased, felspar belongs, or if 

 indeed the rational composition of this mineral may properly be 

 expressed by such formulae, is a question which cannot be dis- 

 cussed, since up to the present time the necessary experimental 

 foundation is entirely wanting. 



May we not expect that fresh experimental investigations de- 

 signed with this object will furnish such data, and that in the 

 future we may possess opinions on the constitution of the sili- 

 cates as well founded as those which we now hold on the consti- 

 tution of the compound ethers and their components ? 



I am not of the opinion of those who deem it impossible to 

 reap in the fields of mineral chemistry a scientific harvest, worthy 

 of the name, by any experimental investigations beyond those of 

 mere quantitative analysis. When we commence investigating 



* Titanite, (|° | o) % ' gj+ (™$ } o) g ; ££, may be regarded as a 

 double calcium- salt of this silicic acid and of the corresponding titanic acid, 

 or as a simple neutral salt containing a mixed acid radical, (tvq [ O J ~ " ~, a - 



