64 Sir H. Davy's Account of some new Experiments 
correct. In experiments on the fluates, it is very difficult to 
exclude sources of inaccuracy; glass vessels cannot be used, 
and even silver and platinum vessels are slightly acted upon 
by the pure fluoric combinations soluble in water. 
Fluor spar decomposed by sulphuric acid increases more 
than three-fourths of its original w'eight; but to produce this 
result several successive distillations of it v»^ith fresh portions 
of acid are necessary, and the spar must be in very fine powder, 
and the result must be powdered after every operation. 
In an experiment made in a crucible of platinum, in which 
very pure white Derbyshire spar was used, and sulphuric acid 
distilled in glass vessels, and in which the product was heated 
to whiteness in every operation, loo grains became in the first 
operation 159.4 grains, which gained 
in the second 
6.9 
in the third 
4.2 
in the fourth 
1-9 
in the fifth 
1.6 
in the sixth 
0.9 
in the seventh - 
0.3 
in the eighth 
-.0 
Total increase 
75-2 
If this result be calculated upon, supposing the number 
representing calcium to be 40, as I have given it in my Ele- 
meius of Chemical Philosophy, the number representing 
fluorine will be 34.2, and fluor spar must be supposed to be 
composed of 40 calcium, and 34.2 fluorine. 
B2 grains of fused subcarbonate of potassa decomposed by 
diluted liquid fluoric acid, in an experiment made with great 
care, was found to afford 18.15 grains of dry fluate of potassa; 
