32 
Proceedings of the Royal Society 
XII. Dry Air^ containing a small quantity of Olefiant Gas . — A 
very small quantity of dry olefiant gas was driven into the absorber 
which contained the dry air already used for Experiment XI. 
Time. 
Pressure. 
Time. 
Pressure. 
m. 
s. 
m. 
s. 
0 
0 
9256*6 
0 
53 
9274*1 
0 
8 
9257*6 
1 
5 
9274*6 
0 
15 
9258*6 
1 
51 
9275*6 
0 
20 
9259-6 
3 
44 
9276*6 
0 
24 
9261*6 
5 
45 
9278*6 
0 
29 
9266*6 
6 
32 
9279-6 
0 
34 
9268*6 
7 
54 
9281-8 
0 
40 
9272*6 
8 
51 
9282-6 
0 
41 
( Steam issuing 
10 
37 
9284*6 
i freely. 
17 
46 
9286*6 
0 
44 
9273*6 
23 
18 
9288*6 
If the above experiments be represented by curves, with intervals 
of time as abscissae and increments of pressure as ordinates, it will 
be seen (1) that the curves have all, except in the case of Experi- 
ment XL, the same general form ; (2) that the curves for dry air 
tend, after different intervals of time, to the same value of ordinate, 
except in the curiously anomalous case of Experiment XI. ; (3) that 
the curves for air containing different quantities of water vapour 
occupy in all cases a lower position on the diagram than those for 
dry air ; (4) that the curve for olefiant gas is above that for dry air ; 
and (5) that the curve for dry air, containing a small quantity of 
olefiant gas, is in the same region of the diagram as those for moist 
air. We thought it worth while, therefore, to try to find how much 
olefiant gas must be added to dry air to give a curve coinciding with 
that of air containing a known quantity of vapour. 
It seemed advisable, however, to increase the radiating surface 
relatively to the surface of the absorber. The apparatus which 
we used for subsequent experiments therefore differed from that 
already described in two respects. The diameter of the cylindrical 
absorber was 18 inches, and the plate separating the radiator K 
from the absorber A was of copper, and in. thick. It was 
made thick to prevent, as much as possible, its giving way under the 
pressure to which it was subjected, when the radiator was in com- 
