452 M. Berzelius on Fluoric Acid. [Dec. 



too high. The remaining liquid, together with the last washings 

 of the silica, was supersaturated with carbonate of soda, mixed 

 with a solution of carbonate of zinc in ammonia, and evaporated 

 nearly to dryness. The silica by being thus combined with 

 oxide of zinc, was not only rendered insoluble, but was reduced 

 to so condensed a state that it could be easily washed. The 

 silicate of zinc, after having been kept in contact for some time 

 with hot water, was transferred upon a filter, and washed. It 

 was then dissolved in nitric acid, the solution was evaporated 

 to dryness, and the residue was digested in acidulated water. 

 The silica, which now remained undissolved, weighed, after 

 ignition, T297 gramme. The alkaline liquid filtered from the 

 silicate of zinc consisted of a mixture of carbonate and fluate of 

 soda. It was saturated nearly but not completely with acetic 

 acid, and evaporated to dryness. The object of not rendering it 

 fully neutral was to avoid the possible dissipation of fluoric acid 

 during the evaporation. The dry mass was treated with a mix- 

 ture of alcohol and acetic acid, in order to extract the slight 

 residue of carbonate of soda, and the fluate of soda obtained by 

 this means in a state of purity, was ignited. It weighed 2-912 

 grammes, equivalent to 0"7S7 gramme of fluoric acid. Conse- 

 quently the whole fluoric acid amounted to 3*053 + 0*787 = 

 3*84 grammes, which had been combined with 5*554 grammes 

 of silica ; that is, in the fluate of silica, 100 parts of fluoric acid 

 are combined with 144*6 parts of siiica. This number, as will 

 be subsequently shown, is not strictly accurate, yet it is a suffi- 

 cient approximation to demonstrate that in this compound, the 

 atomic weight of the fluoric acid has to the atomic weight of the 

 silica the same relation which it has to that of the base in all 

 neutral fluates. 



One of the objects of this analysis was to ascertain the pro- 

 portion of silica which is separated from the gas by the action 

 of water; but the considerable quantity of this earth which is 

 dissolved by the water employed in washing it prevented me 

 from placing any confidence in my direct experimental results. 

 I had recourse, therefore, to the liquid which separates sponta- 

 neously from a saturated aqueous solution of the gas, as it was 

 obvious that from a comparison of its composition with that, of 

 the gas, it would be easy to infer the amount of silica which is 

 deposited. If this liquid be accurately saturated with carbonate 

 of potash, nearly the whole of the acid and silica are precipitated 

 in the state of the insoluble double fluate of silicate and potash, 

 and the remaining fluid, when evaporated to dryness, is found to 

 contain only a mere trace of the same compound. A still more 

 complete precipitation is obtained when the liquid is mixed with 

 an excess of muriate of barytes : here the whole of the acid and 

 silica are precipitated in the state of the double fluate of silica 

 and barytes, and the supernatant fluid contains nothing except 



