338 M. Berselius on Fluoric Acid. [Nov. 



double muriate untouched. The alcoholic solution mixed with 

 water, and abandoned to spontaneous evaporation, was gradually 

 converted into a bright yellow coloured uncrystallized mass. 

 This salt forms a double salt with fluate of potash. 



Saturating Capacity of Fluoric Acid. — Frcm some experi- 

 ments made, on a former occasion, with the utmost attention to 

 accuracy, 1 concluded that 100 parts of pure fluor spar, when 

 decomposed by sulphuric acid, yield 173 - 6'3 parts of sulphate of 

 lime. I had still in my possession the specimen which had fur- 

 nished materials for the preceding determination, and on repeat- 

 ing the analysis with it, I obtained precisely the same result ; 

 but being now better apprized of the circumstance that fluoric 

 and phosphoric acids almost invariably accompany one another 

 in the mineral kingdom, I was induced to examine the specimen 

 more narrowly, and found that it was in fact contaminated with 

 half a per cent of phosphate of lime mixed with some phosphate 

 of oxidule of manganese. I ascertained the presence of these 

 substances by digesting the gypsum in muriatic acid, precipitat- 

 ing by ammonia, and treating the precipitate with water so long 

 as any sulphate of lime passed into solution : the phosphates 

 remained undissolved, and were instantly recognized by their 

 behaviour before the blowpipe. The unavoidable errors attend- 

 ant upon this method of analysis, however, rendered it impossi- 

 ble for me to determine the quantity of the phosphates with 

 perfect precision : I was, therefore, unable to deduce from the 

 experiment the exact saturating capacity of fluoric acid. On 

 this account, I resolved to repeat the analysis with a quantity of 

 artificial fluate of lime, prepared with the utmost precautions to 

 ensure the absence of every foreign admixture. The acid which 

 I employed for this purpose was prepared from pure fluor spar, 

 and distilled sulphuric acid, in a distillatory apparatus of plati- 

 num ; and was received in distilled water, until the liquid began 

 to smoke : in order still more to obviate the possibility of the 

 presence of silica, the first fourth of the acid which distilled 

 over was kept separate. This acid was mixed with a quantity 

 of carbonate of lime insufficient to saturate it completely; and 

 the fluate of lime thus formed was washed in a funnel of plati- 

 num. On the supposition that the salt might still retain some 

 silica, I mixed it with cold concentrated muriatic acid, and at 

 the conclusion of an hour, washed it thoroughly with water. 

 Had the slightest trace of silica been present, it would have 

 been dissolved out by this treatment, in the form of a double salt 

 with the fluoric acid and lime. If fluate of lime, after ignition, 

 can be moistened with fluoric acid without sustaining any 

 elevation of temperature, it may be regarded as absolutely free 

 from silica ; for if the smallest quantity of silica be present, this 

 treatment always occasions a sensible evolution of heat. Of all 

 the filiates which I have examined, the fluate of lime was the 



