ME. G. GOEE ON H YDEOFLU OEIC ACID. 
185 
oxygen had been present, less than two volumes of acid gas would have been produced. 
All the results also support the conclusion that the acid obtained by heat from the double 
fluoride, and that from pure fluor-spar and mono-hydrated sulphuric acid heated together 
in a platinum retort, is free from oxygen and water. The complete synthesis of the acid 
can only of course be performed by means of hydrogen and free fluorine. 
To determine the specific gravity of the anhydrous acid, I employed a thin platinum 
bottle of the form and size of the annexed sketch (fig. 8) ; with the stopper in its 
place the bottle contained 1000 grains of distilled water at 60° Fahr. The stopper had 
a minute tube up its centre, and also two funnel-shaped cavities, one at each end, as shown 
in the sketch. A thin platinum wire was also soldered round the stopper to form a 
Fig. 10. 
shoulder, which rested upon the neck of the bottle when the stopper was tightly down 
in its place. A specific-gravity bottle made of gutta percha w T ould not resist the action 
of the acid. Sponge was employed to absorb the excess of acid around the stopper. The 
specific gravity found of the pure rectified acid in two separate experiments was 0-9885 at 
56°-5 Fahr., that of water being =1000 ; whilst that of a less pure sample was 1-036 at 
60° Fahr. (Sir H. Davy found 1-0609). These results are not perfectly accurate, owing 
to the unavoidable escape of acid vapour, but the amount of error is probably not more 
than 1 part in 1000. The specific gravity of the pure rectified acid was also found by 
weighing a platinum tube (which had been previously filled with paraffin by fusion) 
separately in the acid and in distilled water, both at 52° Fahr. ; the number found was 
0-9922, assuming that of Avater to be =1000 at 52° Fahr. By weighing a closed plati- 
num vessel of the annexed size and form (fig. 9) separately in the acid and in distilled 
water, both at 55° Fahr., the specific gravity found was as 0-9879 is to T0000 ; this 
result is the most accurate one obtained : the pure acid is therefore a little lighter than 
water. The vessel containing the acid was covered by a thin plate of paraffin of the 
annexed form (fig. 10) during the weighing. 
