150 DR WILSON ON THE SOLUBILITY OF 



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glass. Distilled water was then boiled upon powdered fluoi'-spar and filtered 

 whilst hot. It precipitated oxalate of ammonia instantaneously ; and deposited, 

 after cooling, a small quantity of a white precipitate, which answered to the tests 

 of Mme, and, when moistened Avith strong oU of vitriol, gave off an acid which 

 corroded glass. The supernatant liquid likewise precipitated oxalate of ammonia, 

 but more slowly, and yielded, on evaporation, a residue identical in characters 

 with the deposit from the hot aqueous solution. When the deposit or residue 

 was mixed with pounded glass and oil of vitriol, and heated in a flask, a gas was 

 given off which deposited gelatinous silica when passed through water, and had 

 aU the characters of fluosilicic acid. It was manifest from these trials, that water 

 can dissolve fluoride of calcium ; and that it is more soluble in boUing than in 

 cold water. 



The experiments I have mentioned are of so simple and decisive a kind, that 

 the conclusion they warrant cannot be evaded. That no error might arise from 

 impurity of material, many of them were made with water twice distilled, and 

 ascertained to be quite free from foreign matter. On the other hand, specimens 

 of fluor-spar were obtained from diffferent cabinets ; some massive ; the greater 

 number well crystallised. The fluor was finely powdered, and thereafter, in the 

 gi'eater number of cases, digested in warm aqua regia, washed and dried. The 

 only foreign body likely to be present, which could escape removal by this treat- 

 ment, is silica, a substance which would lessen rather than increase the solubility 

 of the fluor. Lest, moreover, the agents employed to purify the fluoride of cal- 

 cium should be supposed to have conferred on it a solubility which it did not ori- 

 ginally possess, other trials were made with native crystals, which, without preli- 

 minary treatment, Avere reduced to powder and boiled with distilled water. In 

 every case solutions were obtained, which, Avhen cooled, yielded a deposit, or, 

 when evaporated, a residue, which gave ofi" hydrofluoric acid when moistened 

 with oil of vitriol, and left sulphate of lime. 



The pieces of etched glass which I shew the Society were corroded by hydro- 

 fluoric acid obtained from the fluoride of calcium previously in solution in water. 

 They will be observed to be as deeply litten in as if undissolved fluor-spar had 

 been made use of Four liquid ounces of the cold aqueous solution will be found 

 to leave sufficient residue to etch glass permanently. The residue from the same 

 amount of solution made at 212" Fahr. will act still more decisively. 



The solution of fluoride of calcium in water at 60° is colourless, transparent, 

 tasteless, and precipitates oxalate of ammonia. Chloride of barium and nitrate of 

 baryta occasion a white precipitate. These reagents act more readily with the 

 solution at 212°. 



The only one of these reactions I have yet found time to examine with any 

 attention is that of the salts of barium. The precipitate they occasion yields 

 hydrofluoric acid abundantly, when treated with oil of vitriol. I have not ascer- 



