520 Proceedings of the Royal Society of Edinburgh. [Sess. 
fifteen minutes the top of the arched capillary neck was raised out of the 
bath, and was instantly sealed by encountering a small blast-lamp flame. 
Two such experiments were made. 
At 352° the vapour pressure of ordinary calomel is 347 mm. The weight 
of 1 c.c. of the vapour at this temperature is therefore 0'002096 g. 
Experiment A . — The drying at room temperature lasted sixty-three days, 
and in the oven eight days. The weight of calomel vaporised was 0T320 g., 
and the volume of the bulb (at 352°) 65'53 c.c. The weight of 1 c.c. found 
is 0002015. The density is therefore normal, and the vapour pressure also 
normal (347 mm.) The drying was presumably insufficient. 
Experiment B . — The drying in the oven lasted five and a half months. 
After the experiment, no calomel was to be seen in the large bulb, but 
a few drops of the nitrates had entered accidentally, through a small 
perforation. The contents of the bulb, however, gave evidence of containing 
the slightest trace of mercury only. The vapour pressure of this dried 
calomel was therefore negligible, as the theory predicts. 
The fact that Baker was able to vaporise the dried substance in the 
form of Hg 2 Cl 2 at 445° remains unexplained. It may be that we reached 
a profounder stage of dryness, at which the volatility disappears. 
The University of Chicago, 
December 1910 . 
(Issued separately July 7 , 1911 .) 
