176 
MR. G. GORE ON HYDROFLUORIC ACID. 
Berzelius found 25*1 per cent, of volatile matter in this salt, and also obtained 11-6 per 
cent, of water by heating the salt with six times its weight of protoxide of lead = T288 
per cent, of hydrogen in it; theory requires 1 ‘2 80 per cent.* In a second trial 800 
grains of the salt, which had been previously fused, was gradually heated to redness ; it 
lost 204-6 grains (=25-575 per cent.), the theoretic quantity of HF being 204*78 grains. 
In a third experiment 2063-6 grains of the salt, which had not been sufficiently heated, 
lost 547 grains (including a little saline matter) in the process of distillation (it should 
have lost only 528 grains) ; for the analysis of the acid obtained from it see page 179. 
2nd. I took another 100 grains of the same salt, dissolved it in water in a capacious 
platinum dish, added 1^ ounce of pure and strong hydrochloric acid, and evaporated 
nearly to dryness, then added more of the acid and slowly heated to perfect dryness, and 
finally to low redness ; the weight of the residue was 95-45 grains, theory requiring 95*47 
grains of chloride of potassium. 
3rd. I now made several attempts to determine the amount of fluorine in the salt by 
means of silica. I took 78-2 grains of the perfectly dry salt, reduced it to fine powder, 
added 50 grains of pure precipitated silica (which was previously found to lose no weight 
by being boiled in strong sulphuric acid), and mixed them together in a platinum bottle ; 
then added in small portions at a time a quarter of an ounce by measure of strong sul- 
phuric acid, and after awhile applied heat gradually until the sulphuric acid was con- 
siderably expelled. The residue was then thoroughly washed in a filter, dried, heated to 
redness, and weighed; it amounted to 19-3 grains=30’7 grains dissolved= 38-56 grains 
of fluorine, theory requiring 38-05 grains. In a second similar experiment 29 - 8 grains 
of silica was dissolved ; in a third, with 40-7 grains of silica, 29‘6 grains was dissolved; 
in a fourth experiment, with 100 grains of silica and half an ounce of the acid, 30T 
grains was dissolved ; and in a fifth experiment, with 50 grains of silica, and a quarter 
of an ounce of water added before addition of the acid, 31-3 grains was dissolved: this 
addition of water appeared to facilitate the action by rendering the mixture more fluid, 
and also by retaining the liberated hydrofluoric-acid gas in solution until it had time to 
act upon the silica. The average quantity of silica dissolved in these five experiments 
was 30-30 grains, theory requiring 30-277 grains. The silica being highly hygroscopic 
was the chief cause of the variation in the numbers obtained ; it was (in some of the 
experiments) cooled and weighed in a stoppered bottle, or in a platinum box (with 
closely fitting lid) in which it had been heated. In similar experiments, with 100 and 
200 grains of purified fine white sand substituted for the precipitated silica, only 6-05 
and 8*5 grains respectively were dissolved ; these results, compared with those obtained 
with the precipitated silica, show that unless the silica is very finely divided, much 
hydrofluoric acid is apt to escape without acting upon it. 
From the results obtained with the precipitated silica I conclude (1st) that the whole 
of the fluorine contained in the salt is evolved as tetrafluoride of silicon, Si F 4 , and not 
any as hydrofluosilicic acid, notwithstanding the presence of water formed by the reaction, 
* Gmelin’s Handbook of Chemistry, vol. iii. p. 65. 
