186 
ME. G-. G-OBE ON HYDBOPLUOBXC ACID. 
The acid obtained in my experiments was much more volatile than sulphuric ether. I 
ascertained its boiling-point as follows. A platinum bottle, A (fig. 11), of about 2^ ounces 
capacity, had a platinum angle-tube, B, which fitted tightly into its neck ; the angle-tube 
had a short open tube, C, within which a platinum tube, D, was tightly fitted and luted 
with the melted sulphur mixture (see page 173) ; this tube was open at its upper end and 
closed at its lower end, and was for the purpose of receiving a thermometer. About 
two ounces of the perfectly pure and previously chilled acid was poured into the chilled 
bottle A, the angle-tube inserted and luted securely with paraffin, the smaller end of the 
angle-tube fixed within the platinum tube of a Liebig’s condenser 
(with freezing-mixture, see page 173) and luted with the paraffin 
mixture. A platinum bottle was affixed to the condenser to 
receive the distillate. The bottle was now immersed in a small 
water-bath, a thermometer placed in the water, another within 
the tube in the acid, and heat very gradually applied to the 
water. The acid boiled at 67° Fahr., the mercury of the inner 
thermometer remaining stationary at that point, and that of the 
outer one at about 77° Fahr., until nearly all the acid had 
passed over. By applying a stethoscope to the end of the inner 
tube D, the boiling could be feebly but distinctly heard ; a slight 
escape of fume at the exit-tube of the receiving-bottle (see page 
174) commenced with the boiling, continued with it, and ceased when the boiling ceased. 
At —30° Faiir. (= — 34^-° C.) the acid is still a perfectly mobile liquid, fuming but 
little in a narrow-necked bottle, and its solidifying point is probably very many degrees 
below this (see also page 198). 
The vapour-tension of the acid at 60° Fahr. is very considerable, and an experiment 
was made in the following manner to approximately determine the degree of pressure 
to which the bottles containing the acid were subjected at ordinary temperatures. A six- 
ounce platinum bottle containing between four and five ounces of the anhydrous and pure 
acid in a chilled state was connected air-tight, by means of the plati- 
num angle-tube A (fig. 12), with an inclined platinum tube B, about 
16 inches ( = 41 ‘7 centims.) long and f- of an inch (=095 centim.) 
diameter, and a vertical bent and open glass tube C, about 30 inches 
( = 76 ‘25 centims.) high and of an inch (=0 - 32 centim.) bore, 
the bent portion of the tubes being filled to about 6 inches (=15*3 
centims.) in height with mercury. The bottle was now gradually 
allowed to attain a temperature of 60° Fai-ir. At that temperature 
the difference of level of the mercury in the two tubes was 15-^ 
inches (=39*4 centims.), and therefore the pressure upon the 
interior of the bottle was =7*58 pounds per square inch. No 
leakage occurred at the cemented joints. The results of this 
experiment, together with those of the previous ones, show the necessity of keeping the 
Pig. 11. 
