150 DR WILSON ON THE SOLUBILITY OF 
glass. Distilled water was then boiled upon powdered fluor-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 lime, and, when moistened with strong oil 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 
all 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 boiling 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 different cabinets; some massive; the greater 
number well crystallised. The fluor was finely powdered, and thereafter, in the 
greater 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, were reduced to powder and boiled with distilled water. In 
every case solutions were obtained, which, when cooled, yielded a deposit, or, 
when evaporated, a residue, which gave off 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 dztien 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- 

