ME. G. GOEE ON HYDEOELTJOEIC ACID. 
18 ; 
From the results obtained, it appears that one volume of hydrogen in uniting with 
fluorine, produces not simply one volume of gaseous product as it does when uniting 
with oxygen, but two volumes, as in the case of its union with chlorine. 
According to M. Peat * anhydrous fluoride of silver contains oxygen, its constitution 
being 1 equiv. of fluorine = 29-6, 1 equiv. of oxygen =8, and 2 equivs. of silver =216. 
The results obtained in these experiments contradict this view ; for according to it the 
volume of gases obtained should have been less, as 1 volume of hydrogen in uniting with 
oxygen produces only 1 volume of gaseous product. 
To obtain a numerical result more nearly approaching theoretical accuracy than in the 
foregoing experiments, various minute corrections would have to be applied : — 1st, for 
the increased capacity of the platinum apparatus caused by its expansion by heat; 
2nd, for the rise of level of the mercury caused by its expansion by rise of temperature ; 
3rd, for the lowering of the said level by expansion of the glass containing-vessel ; 
4th, for the rise of the said level caused by the immersed bulb of the thermometer ; 
5th, for the variation of atmospheric pressure during the experiment; and 6th, for 
the meniscus, &c. 
To ascertain the loss of weight by the fluoride of silver in the preceding experiments, 
12 ’8 grains were put into a platinum boat enclosed in a roll of platinum -foil, and heated 
to tranquil fusion at a gentle red heat in a platinum tube-retort (similar to the tube A 
in fig. 5), then cooled and weighed ; the loss was 0T0 grain. The boat and foil were now 
put into a long horizontal platinum tube and gently heated in a slow current of hydrogen 
(which had been generated by magnesium and pure dilute sulphuric acid, and dried by 
two wash-bottles of strong sulphuric acid), the current of gas and the heat being main- 
tained until acid fumes entirely ceased; the loss of weight was T80 grain. This is 
less than the theoretic quantity' by 0T0 grain, which is partly (if not wholly) accounted 
for by the fact that fluoride of silver, even when carefully prepared from pure materials, 
is liable to contain a variable amount of metallic silver, which is left as an insoluble 
black powder on dissolving the salt in water. This free silver is caused in the process 
of drying the salt, by the aqueous vapour from the imperfectly dried portions and from 
the surrounding air decomposing the dry and hotter portions ; it is increased in quan- 
tity every time the salt is fused in contact with atmospheric air. 
[To determine the amount of silver in the fluoride, 15 - 89 grains of perfectly anhydrous 
fluoride was dissolved in water, the solution filtered, the separated black precipitate 
washed, and the silver in the filtrate determined by addition of chloride of potassium ; it 
gave 18-00 grains of chloride =13-55 grains of silver. The black matter weighed 0-1 
grain after ignition; deducting this amount, the 15-79 grains of fluoride contained 13-55 
grains of silver: theory requires 13-437 grains. On several occasions I have had reason 
to suspect a slight degree of solubility of the separated and finely divided metallic silver 
in a strong aqueous solution of silver fluoride, similar to that of lead and silver in strong 
aqueous solutions of their respective nitrates ; and if this be correct it may account for 
* Comptes Eendus, No. 9, August 1867. 
