28 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
with dry nitrogen, as being the least adsorbible of the chief ingredients 
of air ; if applied to air the results therefore have a “ margin of safety.” 
The apparatus consisted of a glass bulb, holding about 20 grams of 
charcoal, and provided with a bifurcating neck ; one branch of the neck 
was connected to a mercury manometer and to a large burette holding the 
gas over strong sulphuric acid. All gas- volume measurements were made 
at atmospheric pressure. Before being placed in the bulb the charcoal or 
silica was dried by being heated, in vacuo, as strongly as combustion tubing 
would stand ; when in the bulb it was subjected to further heating 
accompanied by intense exhaustion effected by means of cocoanut charcoal 
contained in a large bulb, dipped in liquid air, and connected to the second 
branch of the neck. The evacuating bulb was then shut off, the test-bulb 
plunged in liquid air, and the manometer reading taken by means of the 
micrometer of a cathetometer, using a barometer column (standing alongside 
the manometer) as index. A measured volume of gas was admitted from the 
burette, and an interval allowed to elapse — one of several hours was some- 
times necessary — until the pressure reached stability; the pressure was 
then taken. More gas was admitted, and the operations repeated until 
a sufficient number of results had been obtained. These results enabled 
