1825.] M. Berzelim on Fluoric. Acid. 125 



or outermost crucible, and even of the second, was uniformly 

 coated thickly with silica. 



This salt is not altered by a solution of potash or of carbonate 

 of potash in the ordinary temperatures, but if the mixture be 

 boiled, carbonic acid gas is disengaged, and the whole of the 

 salt passes into solution. In a boiling temperature, the liquid 

 may be concentrated without any deposition ensuing. These 

 effects, however, are not the result of mere solution ; for the 

 salt is decomposed, and the silica gelatinizes in proportion as 

 the liquid cools. Gay-Lussac and Thenard have stated, that a 

 subsalt consisting of silica, potash, and fluoric acid, may be 

 formed by treating the ordinary silicated fluate with caustic 

 potash ; but the precipitate obtained in this manner is nothing 

 else than a mixture of silica with the undecomposed salt. 



Silicated Fluate of Soda. — This salt, whose existence has been 

 denied by Gay-Lussac and Thenard, is almost identical, both in 

 its general appearance and in its chemical characters, with the 

 silicated fluate of potash. It is, however, heavier, and forms 

 larger granules, on which account it subsides more rapidly in 

 the liquid from which it is precipitated ; and I have never 

 observed it, when in this state, reflecting the prismatic colours. 

 It has a gelatinous appearance while moist, but is converted into 

 a fine mealy powder by desiccation. It is much more soluble 

 in water than the salt of potash : it is also more soluble in boil- 

 ing than in cold water, and its solubility is not increased by the 

 presence of an excess of acid. When a saturated solution of 

 the salt is evaporated in a moderate heat, it shoots in small 

 shining crystals, which appear to be regular six-sided prisms, 

 with transversely truncated extremities. The crystals contain 

 no chemically combined water. This salt is acted upon by heat 

 in a similar manner with the preceding, only it retains its excess 

 of acid with much less obstinacy. The introduction of some 

 bits of carbonate of ammonia into the crucible facilitates the 

 dissipation of the last portions of this excess, but in this case 

 the neutral salt which remains is always mixed with sihca. 



Silicatedjiuate oflithia is almost insoluble in water. Its solu- 

 bility is augmented by an excess of acid, and it may be obtained 

 by this means in small transparent crystals, wliich are occa- 

 sionally six-sided prisms, but which have evidently a rhomboid 

 for their basis. When heated, it melts, and obstinately retains 

 its fluate of sihca. 



Silicated Fluate of Anunoniu. — This salt may be formed in the 

 humid way by saturating the liquid acid with ammonia, but the 

 operation is attended with difficulty, because the alkali, even 

 when very dilute, has the property of decomposing the fluate of 

 silica. In the dry way it may be easily prepared by distilling a 

 mixture of the silicated fluate of potash or soda with sal ammo- 

 niac. Thus obtained, it conptitutes <in uncrvstalline mass, but 



