470 PROFESSOR W. RAMSAY AND DR. S. YOUNG ON THE INFLUENCE OE 
higher temperatures which form part of another investigation. The melting-point- was 
found to be 16°’4. 
22. In all these determinations of vapour-pressures by the barometer-tube method, 
the atmospheric pressure was ascertained by a barometer standing in the same trough 
as the experimental tube, and jacketed with flowing water at constant known tempera¬ 
ture. The heights of the mercury in both tubes were read by a mirror-scale standing 
vertically behind them, and were corrected to zero. When necessary, corrections for 
capillarity were applied, but when possible, wide tubes, of approximately the same 
diameter, were employed. 
As every care was taken we are unable to offer any explanation of these capricious- 
results ; they serve at least to account for Regnault's w T ant of success in his attempt 
to solve this problem. 
23. Etliene dibromide was next experimented on, as it was one of the substances 
chosen by R-egnault to decide this question. The new method was employed with 
the following results. The liquid was not quite pure, boiling from 130°-132°. 
Temperature. 
Pressure. 
State. 
millims. 
-1-7 
1*35 
Liquid 
-F9 
1-25 
-1-9 
1-35 
Solid 
Owing to the extremely low pressures, the differences were too small to be measured. 
24. Regnault states that he experimented on carbon tetra-chloride in the solid and 
liquid states. We found no sign of solidification even at —25°, and the bod}’ was 
therefore rejected as unsuitable for our purpose. 
Vapour-pressures of liquid and solid water. 
25. After devising the vapour-pressure apparatus we tested its accuracy by deter¬ 
mining the vapour-pressures of ice and water between —15°'9 and 100°. The results 
agreed well with those calculated by means of Regnault’s formulas; the minute 
differences, however, were not carefully noted at the time, flaving acquired by the 
previous experiments the necessary dexterity of manipulation and accuracy in reading, 
we proceeded to the determination of the vapour-pressures of water and ice at low 
temperatures, which, on account of the extremely small differences to be observed, 
offers greater difficulties. It was first attempted to devise some means of measuring 
accurately small differences of pressure. One device was the use of a barometer and a 
gauge, of the ordinary diameter, to the upper ends of which were sealed narrower tubes 
bent almost at right angles, the bent portions lying in a nearly horizontal position, so 
that a slight alteration of pressure would produce a flow of the mercury through a 
