582 
PROFESSOR GRAHAM ON THE MOTION OF GASES. 
The near approach to equality in the times from 28 to 20, and from 20 to 12 inches 
throughout the whole of these experiments, is very remarkable. Under an average 
pressure of 24 inches in the former portion of the scale and of 16 in the latter, the 
gases effuse with nearly equal velocities ; which confirms the observation of MM. De 
Satnt-Venant and Wantzel, on the passage of air through a minute aperture, 
namely, that above two-fifths of an atmosphere, the further increase of the pressure 
is attended with a very slight increase in the velocity of passage*. In the experiments 
above with an increase of pressure from 16 to 24, or of one-half, the increase in ve- 
locity is not in general more than one-sixtieth part. 
In the table which follows the average times are given, which the gauge barometer 
required to fall from 28 to 12 inches, and from 12 to 4 inches, taken from the pre- 
ceding table, for air, nitrogen and oxygen, and also the ratio between the times of 
these gases, that of air being taken as unity, with their relative velocities, also re- 
ferred to the velocity of air. 
Gauge barometer. 
Time in seconds. 
Time of air = 1. 
Velocity of air = 1. 
Air. 
Nitrogen. 
Oxygen. 
Nitrogen. 
Oxygen. 
Nitrogen. 
Oxygen. 
From 28 to 12 inches. 
242-5 
239 
255-0 
0-9855 
1-0515 
1-0146 
0-9510 
From 12 to 4 inches. 
152-0 
150 
160-5 
0-9868 
1-0558 
1-0133 
0-9470 
These results do not indicate any material difference between the ratios of effusion 
of these gases at different pressures. At the low as well as the high pressure, the 
velocities are in close accordance with the law of effusion ; indeed they correspond 
as closely as the shortness of the time of observation justifies any inference ; the small 
deviations observable being quite within the amount of errors of observation. 
The results for the mixtures of oxygen and nitrogen are as follows, for similar 
divisions of the scale : — 
Time in seconds. 
Time, air = 1. 
Gauge barometer. 
I. 
50 N + 50 0. 
II. 
25 N + 75 O. 
III. 
75 N + 25 O. 
I. Mixture. 
II. Mixture. 
III. Mixture. 
From 28 to 12 inches. 
247 
252 
243-5 
1-0185 
1-0391 
1-0041 
From 12 to 4 inches. 
155 
157 
153 
10197 
1-0329 
1-0066 
In these instances, as well as in the unmixed gases, the results do not justify the 
inference of any difference in the ratios of effusion at low from the ratios which hold 
at high pressures. 
It appears, on comparing the times observed of the mixtures with the times calcu- 
lated from the unmixed gases, that they sensibly agree. Thus the mean rate or time 
* Journal de l’Ecole Royale Polytechnique, tome xvi. 27 me Cahier, 1839, p. 85. This memoir contains a 
valuable mathematical discussion of the velocities with which air flows into a receiver at different degrees of 
exhaustion. 
