PROFESSOR GRAHAM ON THE MOTION OF GASES. 
579 
These results, referred to air as unity, are as follows : — 
Time of effusion. 
Theoretical time. 
Velocity of 
effusion. 
Theoretical 
velocity. 
Air 
Nitrogen 
Oxygen 
Hydrogen 
Carbonic acid 
I 
0*9842 
1*0502 
0*2763 
1*1971 
1 
0*9856 
1*0515 
0*2632 
1*2365 
1 
1*0160 
0*9503 
3*607 
0*8354 
1 
1*0146 
0*9510 
3*7994 
0*8087 
The experimental results of the velocity of effusion of nitrogen and oxygen accord 
very closely with theory, the velocity of the first being only 0'0014 in excess, and the 
second 0‘0007 in deficiency. Indeed the differences fall within the unavoidable 
errors of observation in determining the specific gravity of these gases, unless con- 
ducted with the greatest precautions. Of hydrogen, the velocity of effusion observed 
is 3 607 times instead of 3'80 times greater than air. It thus suffers a small but 
sensible reduction of its velocity, which can be referred, as will afterwards appear, 
to the thickness of the plate and the aperture being in consequence sensibly tubular. 
A portion of the carbonic acid gas must have been absorbed by the brine during the 
long continuance of the experiment, nearly an hour; to which the quickness of the 
rate of that gas may be referred ; the velocity of its passage being thus apparently 
increased from 0'81 to 0‘835. 
The experiment was varied by observing the time in which gas entered a vacuous 
receiver upon the plate of the air-pump, in quantity sufficient to depress the gauge 
barometer from 28 to 23 inches. An exhaustion was always made at first of upwards 
of 29 inches, and the instant noted at which the mercury passed the 28th and 23rd 
inches of the scale. The times of effusion were as follows, the temperature being 66°. 
Experiments. 
Velocity of effusion. 
1. 
2. 
3. 
Mean. 
Observed. 
Calculated. 
Air 
474 
501 
468 
467 
357 
573 
474 
502 
469 
469 
573 
474 
500*7 
468*5 
468 
337 
573 
1 
0*9467 
1*0117 
1*0128 
1*3278 
0*8272 
1 i 
0*9510 
1*0146 
1*0147 
1*3369 
0*8087 
Oxygen 
Nitrogen 
Olefiant gas 
Carburetted hydrogen 
Carbonic acid 
499 
The same close correspondence is manifest here between the observed and calcu- 
lated velocities. 
The whole results leave no doubt of the truth of the general law, that different 
gases pass through minute apertures into a vacuum in times which are as the square 
roots of their respective specific gravities ; or with velocities which are inversely as the 
square roots of their specific gravities ; that is, according to the same law as gases 
diffuse into each other. 
It appears that the proper effect of effusion can only be brought out in a perfect 
4 f 2 
