244 Dr Davy's Experiments cni Silicated Fltioric Acid Gas. 



dry tube, and filled with clean and dry mercury ; on the admis- 

 sion of the silicated gas, the combination of the two was instant, 

 and accompanied by the bright ignition of the whole mass. If 

 the experiment was less carefully made, there was no immediate 

 action on the introduction of the gas ; it was either not absorbed 

 at all, or very slowly, and to a small extent ; and yet, when 

 heat was applied by means of a spirit-lamp, the combination was 

 sometimes effected rapidly with ignition. Occasionally, how- 

 ever, even a dull red-heat did not effect an union. In the in- 

 stances of failure, it appeared to be owing either to a superficial 

 crust formed on the line, connected with humidity, which de- 

 fended the interior from the action of the acid, or to the pre- 

 sence of some carbonate of lime, or even of its hydrate, which 

 had a similar eflPect. In the best experiments, I carefully 

 sought for oxygen in the residual gas ; but never found it ; the 

 little gas that remained proved to be either silicated fluoric acid 

 gas in mass, or common air that had adulterated it. This ab- 

 sence of oxygen proved, that the silicated fluoric acid gas had 

 united directly with the lime. 



The compound of the silicated fluoric acid and lime, was 

 tasteless ; had no effect on litmus or turmeric paper ; appeared 

 to be insoluble in water ; before the blowpipe it phosphoresced, 

 emitting a brilliant bluish-white light, — and when urged by the 

 flame, softened, and the particles were agglutinated into a mass 

 of such hardness as to scratch glass. With strong sulphuric 

 acid it effervesced powerfully, almost like carbonate of lime, — 

 giving off silicated fluoric acid gas. Muriatic acid acted on it 

 slowly, converting it, I believe, into subsilicated fluate of lime 

 (the fluate of silica and lime of Berzelius), which was dissolved, 

 a little silica remaining undissolved in a gelatinous state. 



From the quantity of anhydrous sulphate of lime which 

 has been obtained from it, when decomposed by sulphuric acid, 

 it appears to consist of two proportions of lime and of one of si- 

 licated fluoric acid ; thus, in one experiment, 1.9 grains of it gave 

 2.35 of sulphate of lime ; and, in another, 1 .65 of it afforded 

 2.04. The latter result I consider the best : however, the quan- 

 tity being so small, at best it can only be received as an approxi- 

 mation. As the idea of this composition, and considering fluor- 

 spar composed of one proportion of fluorine and of one of calcium 



