454 M. Berzelius on Fluoric Acid. [Dec. 



that is, containing no water, except the quantity which acts the 

 part of a base. Thus I have distilled the silicated filiate of 

 barytes with concentrated sulphuric acid, but there was disen- 

 gaged at the commencement of the process a large quantity of 

 the gaseous filiate of silica, which gelatinized in water, and 

 towards the conclusion, there passed over an acid liquid, which 

 consisted in a great measure of concentrated fluoric acid. Even 

 the silicated filiates, such as those of copper or nickel, which 

 contain much water of crystallization, afforded similar results. 

 The dilute acid may be concentrated by evaporation, but after it 

 attains a certain degree of strength, it begins to evaporate in an 

 equal proportion with the water : it may also be concentrated 

 over sulphuric acid in vacuo, but long before it acquires the 

 above-mentioned strength^ it evaporates along with the water, 

 and corrodes the receiver. The best method of obtaining this 

 acid in a state of concentration is to add finely pulverised silica 

 in small quantities at a time to fluoric acid, diluted with twice 

 or thrice its weight of water, and artificially cooled. It dissolves 

 the silica readily until it attains the composition of the liquid 

 acid ; what it takes up beyond this point is immediately after- 

 wards dissipated in the form of gas. 



When the double silicated filiates which contain water of 

 crystallization are exposed in a glass vessel in so high a temper- 

 ature that the fluate of silica begins to be expelled, there is 

 obtained a white sublimate which might be readily mistaken for 

 an ammoniacal salt, but which, when examined by a micro- 

 scope, is found to consist of transparent drops. This liquid may 

 be distilled unaltered from one part to another so long as the 

 vessel is filled with the gaseous fiuate of silica, but it deposits 

 silica as soon as the gss is replaced by atmospheric air. It 

 requires a pretty high temperature for volatilization. 



There is a particular degree of concentration which the liquid 

 acid uniformly acquires when exposed for some time to the air ; 

 when weaker than this, the excess of water evaporates; when 

 stronger, it very rapidly absorbs moisture from the atmosphere. 

 In a temperature of about 104°, it slowly evaporates without 

 leaving any residue, and towards the conclusion of the evapora- 

 tion, it deeply corrodes any glass vessel in which it may have 

 been kept. 



The gaseous fluate of silica is rapidly absorbed by alcohol 

 without decomposition, but as soon as the liquid becomes nearly 

 saturated, it stiffens to a clear transparent jelly. The alcohol 

 when saturated contains more than half its weight of the gas, 

 and has an odour of ether. Petroleum also absorbs the gas 

 unaltered, but only in small quantity. 



The liquid silicated fluoric acid combines with all the bases, 

 and forms with them peculiar salts. I have subjected to a regu- 

 lar analysis the double salts of potash, soda, barytes, and lime, 



