1'26 M. Berzeliiis on Fluoric Acid. [FeIjI 



if it be dissolved in water, and the solution committed tosponta*. 

 neous evaporation, it shoots in large transparent crystals. The 

 primary form of its crystal is the rhomboid, and, like the preced- 

 ing salts, it has a strong tendency to assume the form of a short 

 six-sided prism. This salt is very soluble in water. Ignited, it 

 decrepitates slightly, and sublimes unaltered ; and a glass retort 

 may be employed for this experiment without undergoing corro^ 

 sion. Ammonia decomposes the aqueous solution of this salt, 

 but if the filtered liquid (which still retains some silica in solu- 

 tion) be evaporated, a certain quantity of the alkali is volatilized, 

 and a portion of the double salt is regenerated, in consequence 

 of the silica being redissolved by the disengaged acid. 



Gay-Lussac and J. Davy have shown that the gaseous fluate 

 of silica and ammoniacal gas occasion mutual condensation, 

 when mixed in the proportion of two volumes of the foimer to 

 one volume of the latter. The product is a white pulverulent 

 salt, which may be subbmed unaltered, so long as it is kept free 

 from moisture. When put into water, it is decomposed, and 

 the silica evaporates in a gelatinous state, according to J. Davy ; 



. a proof that it had been chemically combined with the other 



ino-redients of the salt. This compound appears, therefore, to 

 consist of an atom of anhydrous fluate of ammonia and an atom 

 of anhydrous silicate of ammonia ; and it probably belongs to 

 the class of salts styled fluosilicates. 



Silicatedjiuate of harytes is best obtained by mixing a solution 

 of muriate of barytes with the liquid acid : after a few moments 

 it precipitates in minute crystals, and the liquid contains disen- 

 gaged muriatic acid. It is so little soluble in water that nearly 

 the whole of the barytes may be in this manner precipitated, and 

 its solution is not sensibly promoted by the excess of muriatic 

 acid. Its crystals are prisms, with very long acuminations. It 

 contains no water of crystallization. When heated, it- is easily 

 decomposed, and there remains neutral fluate of barytes. 



Silicated Jiuate of lime may even be obtained by digesting a 

 mixture of pulverised fluor spar and siHca in muriatic acid; but 

 the most certain method of preparing it is to add carbonate of 

 lime to the liquid acid so long as it continues to dissolve. This 

 salt is insoluble in water, unless when assisted by an excess of 

 acid, and it crystallizes as this excess evaporates. The crystals, 

 which are well characterized, appear to be four-sided prisms 

 with obhquely truncated terminations. When digested in water, 

 this salt is partially decomposed ; fluate of lime and silica being 

 precipitated, while the liquid silicated fluoric acid which is in 

 this manner disengaged, retains the remainder of the double salt 

 in solution. 



Silicatedjiuate of strontian is easily soluble in water, contain- 

 ing an. excess of acid, and may be obtained in large crystals by 

 evaporation These crystals are short four-sided slightly oblique 



