278 Dr. J. E. Reynolds on certain Mineral Silicates. 



In addition to this, a simple explanation is also afforded of the 

 causes of the great variation in the characters of silica, whether 

 obtained native or prepared artificially. I would further suggest 

 that tbe recent researches of M.Debray* on the phospho-molybdic 

 acids bear very strongly upon the same point. But very recently 

 some particularly well-defined and crystallized compounds of 

 phosphoric and molybdic acids have been discovered by M. De- 

 bray, the composition of which shows that molybdic acid is 

 capable of undergoing an amount of molecular condensation of 

 which we had previously no conception. This is best illustrated 

 by the formulae of the silver-salts of two of these phospho- 

 molybdic acids. The old notation is that employed by the 

 author. 



(1) 7AgO, (PO 6 , 20MoO 3 ) + 24HO, 



2 AgO, (PO 5 , 20MoO 3 ) + 7 HO. 



(2) 6AgO, (2P0 5 , 10MoO 3 ) + 14HO. 



It would thus appear that we have not only M0O 3 , but at least 

 two other polymers of this — Mo 5 O 15 and Mo 20 O 60 . It is well 

 worthy of remark that the first of these two bodies can be ob- 

 tained only from alkaline solutions, and the second only from 

 acid liquids, and one modification can be speedily changed into 

 the other by simply realizing either condition. Tungstic acid 

 has been found to possess similar power of atomic condensation. 



Molybdic, tungstic, and silicic anhydrides and acids are well 

 known to present many chemical analogies ; the proof of this 

 power of condensation in the cases of molybdic and tungstic 

 acids, combined with our previous knowledge of the silicic hy- 

 drates and of silica itself, warrants us in attributing the same 

 power to silicic acid, more particularly when we shall find the 

 composition of the silicates and their relations to be easily expli- 

 cable on such a view. In reality, however, this is nothing more 

 than the adaptation of one of the well-known principles of organic 

 chemistry relating to the condensation of radicals — the mode of 

 generation of compounds of this order being thus precisely stated 

 by M. Wurtzf to be " based on the one hand upon the principle 

 of the accumulation of polyatomic radicals, and on the other hand 

 upon the successive dehydration which may be undergone by hy- 

 drates containing polyatomic radicals." 



The plan upon which I construct the formula of the silicates 

 is as follows : — Instead of writing a unisilicate or a bisilicate 



^Ao 4 and ^ 2 1>0 3 with Odling or Wurtz, 



* Chemical News, vol. xvii. p. 183. 



t Crookes's translation of Wurtz's ' Modern Chemical Philosophy.' 



