666 Vapour-Pressure of Mercury at Ordinary Temperatures. 
volume was determined by means of two experimental gas- 
meters. 
One experiment at 50° was lost by projection of mercury, 
and when the experiment was repeated, it was so done as to 
give convincing proof that the current of gas used was per- 
fectly saturated with mercurial vapour. Two absorption 
apparatus were put in series. Hydrogen was produced by 
the action of hydrochloric acid on zine, washed with solution 
of potassium hydroxide, and dried with ‘phosphorus pentoxide. 
The regulated current passed first through one of the two 
absorption apparatus ; since it required a pressure of one inch 
of mercury to force the gas through the second apparatus, the 
volume of the gas was now one thirtieth less than il. became 
after passing through the second absorption apparatus. If, 
then, the gas was saturated with mercurial vapour in the first 
apparatus, it would still take up one twenty-ninth as much 
mercury in expanding to its final volume in the second 
absorption apparatus. By reference to the second experiment 
at the temperature 50°, it will be seen that the quantity taken 
up from the second absorption apparatus was this twenty- 
ninth part, and that therefore it is satisfactorily proved that the 
current of gas was perfectly saturated with vapour of mercury. 
lt may be-added that, after a few hours, the current of gas 
always passed through the mercury in a thin film and not in 
bubbles, and that the diffusion of vapour through this thin 
fiim could not but be rapid. 
The following table gives the temperature of the mercury 
and of the gas-meter in each experiment, the volume of gas 
at the meter and in the act of passing through the mercury, 
the loss of weight of the mercury, and the loss for one litre 
of gas :— 











Temp. | Temp. of | Volume | Volume |Loss of weight) Loss per 
of mercury. gas-meter. at meter. at mercury.| of mercury. litre. 
is ees Jon IDE mg. meg. 
40:0 13°6. hy, 2OT7 325°2 17°25 0-053 
ait, ‘s 257°0 280°7 15°57 0-056 
60°0 10°3 153°2 176°7 36 60 0:207 
As i 115 0 132°6 27°15 0-205 
70:0 19:0 105°2 1236 46°89 0:379 
" ie 91:3 107-2 40°31 0-376 
50°0 18°5 147-5 1638°5 1811 Oli 
* heeaae Ey briicois | : 
“ 17-0), ply 2280 253'9 i 0-9 } | 0-113 
30:0 16°4 246'1 2578 T30b 00285 
, 16-7 288°7 301'9 | 3:23 0:0273 







The following table gives the mean values adopted for each 
