1869.] 



Mr. G. Gore on Hydrofluoric Acid. 



257 



A number of attempts were made, finally with success, to determine the 

 molecular volume of the pure anhydrous acid in the gaseous state, the acid 

 in these cases being prepared by heating pure anhydrous fluoride of silver 

 with hydrogen in a suitable platinum apparatus over mercury. Particulars 

 are given of the apparatus employed and of the manipulation. The results 

 obtained show that one volume of hydrogen, in uniting with fluorine, pro- 

 duces 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. 

 The gaseous acid transferred to glass vessels over mercury did not corrode 

 the glass, or render it dim in the slightest degree during several weeks, pro- 

 vided that moisture was entirely absent. 



The author concludes that the anhydrous acid he has obtained is destitute 

 of oxygen, not only from the various analyses and experiments already re- 

 ferred to, but also, 1st, because the double fluoride from which it was pre- 

 pared, when fused and electrolyzed with platinum electrodes, evolved 

 abundance of inflammable gas at the cathode, but no gas at the anode, al- 

 though oxides are by electrolysis decomposed before fluorides ; 2nd, because 

 the electrolysis of the acid with platinum electrodes yielded no odour of 

 ozone, whereas the aqueous acid of various degrees of strength evolved that 

 odour strongly ; and, 3rd, because the properties of the acid obtained from 

 hydrogen and fluoride of silver agree with those of the acid obtained 

 from the double salt. He considers also that the acid obtained from pure 

 fluor-spar and monohydrated sulphuric acid heated together in a platinum 

 retort is free from oxygen and water. 



The specific gravity of the anhydrous liquid acid was several times de- 

 termined, both in a specific-gravity bottle of platinum, and also by means 

 of a platinum float submerged and weighed in the acid. Concordant and 

 reliable results were obtained; the specific gravity found was 0'98/9 at 

 55° Fahr., that of distilled water being= 1*000 at the same temperature. 



The anhydrous acid was much more volatile than sulphuric ether. Its 

 boiling-point was carefully determined in a special apparatus of platinum, 

 and was found to be 67° Fahr. Not the slightest sign of freezing occurred 

 on cooling the acid to —30° Fahr. (= — 34 0, 5 C.) ; and it is highly probable 

 that its solidifying temperature is a very great many degrees below this. 

 Its vapour-tension at 60° Fahr. was also approximately determined, and 

 was found to be =7'58 lbs. per square inch. On loosening the lid of a 

 bottle of the acid at 60° Fahr., the acid vapour is expelled in a jet like 

 steam from a boiler ; this, together with the low boiling-point, the extremely 

 dangerous and corrosive nature of the acid, and its great affinity for water, 

 illustrates the very great difficulty of manipulating with it and retaining it 

 in a pure state. Nevertheless, by the contrivances described, and by placing 

 the bottles in a cool cellar (never above a temperature of 60° Fahr.), the 

 author has succeeded in keeping the liquid acid perfectly, without loss and 

 unaltered, through the whole of the recent hot summer. 



The electrical relations of different metals &c. in the acid were found to 



