[ 173 ] 
V. On Hydrofluoric Acid. By G. Gore, F.R.S. 
Received November 14, 1868, — Read January 28, 1869. 
A. Anhydrous Hydrofluoric Acid. 
The method I have adopted to obtain this compound is the same as that employed by 
Fremy*, viz. to heat to redness dry double fluoride of hydrogen and potassium in a 
suitable platinum apparatus. 
As the results I have obtained differ somewhat from those described by Fremy, and 
as the anhydrous acid has been considered to be a gas by him and by several other able 
investigators f, it will be necessary for me to state with a sufficient degree of minuteness 
the conditions of my experiments. 
Pure aqueous hydrofluoric acid, prepared by the method described in this paper 
(page 196), and free from sulphuric, sulphurous, hydrosulphuric, hydrochloric, and 
hydrofluosilicic acid, also from sulphur, arsenic (except minute traces), and all fixed 
substances, was added to carbonate of potassium (free from chlorides, sulphates, and 
silica) in a large platinum dish, until the liquid on evaporation evolved a distinct 
acid odour, and the vapour reddened litmus-paper. The clear solution was evaporated 
to perfect dryness, and the residue gently heated until it fused to a clear thin liquid, 
free from films upon its surface ; it evolved a trace of acid vapour during the process, 
and did not corrode the platinum vessel. The salt when cooled formed a rather hard, 
white, non-deliquescent mass ; but if the acid was in much excess the fused salt had 
tough films upon its surface, and formed on cooling a less hard, less white, and more 
transparent mass. 
To obtain the acid from this salt, about 2800 grains Kg- 1- 
weight of fragments of the substance was put into a platinum 1 I 
retort of the annexed form (fig. 1), about 6 inches ( = 15 ’3 J 1 
centimetres) deep and 1^ inch (=3 - 8 centimetres) diameter, 
and gently heated to complete fusion to expel any traces of 
water. The vessel was then fitted air-tight (by means of 
melted sulphur mixed with lampblack) to a closely fitting 
platinum tube, about 36 inches (=91-5 centimetres) long, of 
a Liebig’s condenser, A (fig. 3), the condenser being supplied 
with a freezing-mixture, composed of 1 part of pounded ice 
* Ann. de Chimie (3), vol. xlvii. p. 5 ; Comptes Rendus, No. 9, Feb. 27th, 1854. 
f Vide Fremt, Comptes Rendus, No. 9, Feb. 27th, 1854; Louvet, Comptes Rendus, vol. xxii. p. 960; also 
Miller, Elements of Chemistry, part 2, 4th edition, p. 161. 
MDCCCLXIX. 2 B 
