in different chemical Processes on Fluor Spar. 409 
very heavy elestic fluid, its specific gravity being nearly 
forty-eight times as great as that of hydrogen. It produces, 
according to my brother Mr. John Davy, a quantity of si- 
lica equal to 742; of its own weight by its action upon 
water, and a quantity equal to ;%},% of its weight by its ac- 
tion upon solution of ammonia. It condenses twice its 
own volume of ammonia, and forms a solid salt, volatile 
when free from water without decomposition. 
Liquid fluoric acid, the second of these substances, was 
discovered by Scheele, but first obtained in its pure form 
by MM. Gay-Lussac and Thenard. It is proeured by 
heating concentrated sulphuric acid and pure fluor spar, in 
retorts of silver or lead, and receiving the product in re- 
ceivers of the same metals artificially cooled. It is a very 
active substance, and must be examined with great caution. 
According to my experiments, its specific gravity is 1-0609*. 
It produces a high degree of heat when mixed with water ; 
and such is its degree of attraction for water, that it be- 
comes denser by combining with that fluid. By adding 
water, in very small quantities at a time, to pure liquid 
fluoric acid, I found that its specific gravity gradually in- 
creased till it became 1°25; it is, I believe, the only known 
body possessed of this property. 
The third substance is fluo-boric acid gas, which was dis- 
covered by MM, Gay-Lussac and Thenard. It is pro- 
duced by intensely heating, in an ‘iron tube, a mixture of 
dry boracic acid and fluor spar, or by gently heating ina 
glass retort a similar mixture with sulphuric acid. Its spe- 
cific gravity is rather more than thirty-two times as great 
as that of hydrogen. It forms a solid salt, volatile without 
decomposition, by condensing its own volume of ammonia, 
The ammoniacal salt dissolved in water and distilled, af- 
fords boracic acid. 
The most important phenomena of chemical change, in 
which these bodies operate, that may be supposed to illus- 
trate their nature, is their agency upon potassium and other 
metals, The action of potassium upon silicated fluoric 
gas has been already referred to. MM. Gay-Lussac and 
Thenard, by heating potassium and sodium in fluo-boric 
acid gas, obtained fluate of potassa or soda, and the basis 
of the boracic acid; and by exposing potassium to liquid 
fluoric acid, their results were hydrogen and acid fluate of 
potassa, 
* Unless it is distilled through tubes and into vessels of pure silver, its 
specific gravity is greater; it readily dissolves tin, and slowly dissolves lead, 
and after being long kept in vessels of pure silver, it is found to have taken 
up a small portion even of that metal, 
Three 
