130 M. Berzelius on Fluoric Acid. [Feb, 



priate. Thus the topaz consists of an atom of subfluate of 

 alumina combined with nine atoms of silicate of alumina ; and 

 pi/cnite, of an atom of the neutral fluate combined with nine 

 atoms of the silicate. 



During the decomposition of the silicated fluates by the caus- 

 tic alkalies, particularly by ammonia, it is possible that other 

 fluosilicates may be produced, in which the relative proportions 

 of the fluate and silicate may vary with the different circum- 

 stances under which the compounds are formed. I have not 

 investigated this subject so minutely as it deserves, and indeed 

 1 have confined myself to the decomposition of the silicated 

 fluate of lime by ammonia, as being that of which an accurate 

 knowledge is at present most interesting, because the preci- 

 pitates which result from this decomposition occasionally make 

 their appearance during the analysis of minerals. A mixture of 

 finely pulverized fluor spar and of ignited silica in the state in 

 which it is obtained from the decomposition of the fluate of silica, 

 was digested with muriatic acid in a closely stopped glass vessel, 

 from which no vapours of fluate of silica could escape. At the 

 end of 48 hours, the clear liquid was mixed with ammonia, and 

 the precipitate was washed and ignited. Decomposed by sul- 

 phuric acid, this precipitate gave off gaseous fluate of silica, 

 which was received in carbonate of soda, and left 136 per cent, 

 of sulphate of lime. The alkaline solution was evaporated to 

 dryness in a moderate heat ; and the residue, being digested in 

 water, left 22* 11 per cent, of silica. The remaining liquid was 

 saturated with acetic acid, exposed to the air for 24 hours, in 

 order to ensure the dissipation of the carbonic acid, mixed with 

 ammonia, and precipitated in a stoppered vessel with muriate of 

 lime. The fluate of lime thus obtained weighed, after ignition, 

 78 per cent. The precipitate was composed, theretbre, of 

 neutral fluate of lime and of silica in the proportions requisite to 

 form with fluoric acid the liquid silicated fluoric acid. Whether 

 the silica actually existed in a state of chemical union is doubt- 

 ful, but it appears to be rendered probable by the fact, that the 

 neutral alkaline fluates are capable of dissolving sihca in a red 

 heat without undergoing decomposition. 



Another portion of the same solution in muriatic acid was 

 mixed with muriate of lime, and decomposed by ammonia. The 

 precipitate, analj'zed in the same manner as the preceding, 

 yielded 150 per cent, of sulphate of lime = 62-25 per cent, of 

 lime, 19 per cent, of silica, and 65'67 per cent, of fluate of lime 

 = ]8*04 of fluoric acid. It appears, therefore, to have been 

 composed of an atom of bisilicate and three atoms of fluate of 

 lime. The precipitate formed by ammonia in a solution of apo- 

 phyllite in cold nitric or muriatic acid, and which many chemists 

 have mistaken for alumina, possesses an exactly similar compo- 

 sition. If the mineral be dissolved with the assistance of heat. 



