650 
ON HYDROFLUORIC ACID. 
fluoride of hydrogen and potassium to redness in a suitable platinum apparatus (shown 
by a figure accompanying the paper), and states the conditions under which it may be 
obtained in a state of purity. 
The composition and purity of the anhydrous acid are shown and carefully verified by 
various methods of analysis, both of the double fluoride from which it was prepared and 
of the acid itself; and particulars are given of all the circumstances necessary to ensure 
reliable and accurate results. Nearly all the operations of preparing, purifying, 
analysing, and examining the properties of the acid were conducted in vessels of plati¬ 
num, with lutings of paraffin, sulphur, and lampblack; articles of transparent and 
colourless fluor-spar were also employed in certain cases. Nearly all the manipulations 
with the acid were effected while the vessels containing it were immersed in a strong 
freezing-mixture of ice and crystallized chloride of calcium. 
The pure anhydrous acid is a highly dangerous substance, and requires the most 
extreme degree of care in its manipulation. It is a perfectly colourless and transparent 
liquid at 60° F., very thin and mobile, extremely volatile, and densely fuming in the 
air at ordinary temperatures, and absorbs water very greedily from the atmosphere. It 
was perfectly retained in platinum boltles, the bottle having a flanged mouth with a 
platinum plate secured with clamp-screws, and a washer of paraffin. 
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 pla¬ 
tinum 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, 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. 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, provided 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 referred to, but also— 
1st, because the double fluoride from which it was prepared, when fused and electro¬ 
lysed with platinum electrodes, evolved abundance of inflammable gas at the cathode, 
but no gas at the anode, although oxides are by electrolysis decomposed before fluo¬ 
rides ; 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 con¬ 
siders 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 determined, both 
in a specific-gravity bottle of platinum, and also by means of a platinum float sub¬ 
merged and weighed in the acid. Concordant and reliable results were obtained ; the 
specific gravity found was (F9879 at 55° F., 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° F. 
Not the slightest sign of freezing occurred on cooling the acid to — 30° F. (— — 35 5° C.); 
and it is highly probable that its solidifying temperature is a very great many degrees 
below this. Its vapour-tension at 60° F. 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°F. 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° F.), the author has suc¬ 
ceeded in keeping the liquid acid perfectly, without loss and unaltered, through the 
whole of the recent hot summer. 
The electrical relations of different metals, etc., in the acid were found to be as fol¬ 
lows at 0° F.:—Zinc, tin, lead, cadmium, indium, magnesium, cobalt, aluminium, iron, 
nickel, bismuth, thallium, copper, iridium, silver, gas-carbon, gold, platinum, palladium. 
