182 
MR. G. GORE ON HYDROFLUORIC ACID. 
of the acid vapour. In all cases, however, the contraction of volume was evidently 
nearly wholly due to the partial condensation of the hydrofluoric-acid vapour within the 
vessel to a liquid state. This liquid could not of course be seen on account of the opa- 
city of the apparatus, and being very minute in amount (probably less than half a drop 
for each cubic inch (=16-387 cub. centims.) of hydrogen employed) and very volatile, it 
was in all cases instantly converted into a dense fume on opening the vessel. The mere 
warmth of the hand was sufficient to make the partly liquefied acid expand very greatly. 
These results of contraction agree with and confirm the results already found in my ex- 
periments, viz. that anhydrous hydrofluoric acid is a very volatile liquid at 60° Fahr. 
The following are the actual results obtained in one of the first reliable approximate 
experiments. Six cubic inches ( = 98-322 cub. centims.) of prepared hydrogen at 50° 
Fahr. and 16-4 grains of fused fluoride were employed. During the first three minutes 
of heating, the gas expanded to 7'8 cubic inches (=127‘8 cub. centims.). Contraction 
then commenced and continued during about twenty-five minutes, the volume being 
gradually reduced to about 4^ cubic inches (=73-74 cub. centims.). The heat was con- 
tinued about half an hour longer, and the apparatus then, whilst still warm, placed in the 
air-bath, and heated gradually to a fixed temperature of 200° Fahr. ; the volume of gas 
was then 14-5 cubic inches (=237-61 cub. centims.) =11-2 cubic inches (=183-53 cub. 
centims.) at 50° Fahr. The rate of expansion was somewhat greater at the higher de- 
grees of temperature than at the lower ones; for instance, at 139° Fahr. the volume 
was 12-1 cubic inches, at 160° Fahr. 12-85, at 186° Fahr. 14-0. Only a minute 
quantity of undecomposed silver fluoride was found after the experiment. 
In another experiment, with 5-5 cubic inches (=90-128 cub. centims.) of hydrogen 
at 50° Fahr. and standard pressure, and 15 "3 grains of fluoride, on applying heat the 
gas expanded to 7 - 3 cubic inches ( = 119-625 cub. centims.) at the end of three minutes; 
it then gradually contracted during the next twenty minutes to about 4*2 cubic inches 
( = 68-825 cub. centims.); the heat was continued about twenty minutes longer with 
occasional heating to full redness (but not sufficient to fuse the enclosed reduced silver). 
The apparatus was then at once transferred to the hot air-bath, and heated gradually to 
212° Fahr., and kept at that temperature some time. The volume of gas thus ,found 
was 12-8 cubic inches (=209-75 cub. centims.) at 176°Fahr., 13-0 (=213*03 cub. cen- 
tims.) at 184° Fahr., and 14-0 (=229-418 cub. centims.) at 212° Fahr. ; the latter number, 
after correction for the amount of displacement of the level of the mercury by the thick- 
ness of the sides of the platinum vessel between “ 5-5,” the original depth of immersion, 
and “14” the final one, was 14-3 (=234-33 cub. centims); this is equal to 10-84 
cubic inches (=177-635 cub. centims.) at 50° Fahr., the theoretic quantity required 
being 11-0 inches (=180-257 cub. centims.). On cooling the apparatus to 50 a FAHR., the 
mercury rose and filled the platinum tube to within about 0-7 cubic inch (=1T77 cub. 
centims.) of its capacity, even whilst under rarefaction by a column of mercury about 
3-5 inches (=8-9 centims.) in height. Minute traces only of undecomposed fluoride of 
silver were found in the tube after the experiment. 
