450 
SECOND REPORT— - 183 &. 
correspond very closely, showing that the theory is probably a 
true expression of the phenomena. 
Granting the existence of a law of nature by which gases are 
induced to diffuse themselves mutually as liquids do, and as 
solids in solution do, it might be supposed that the difference 
of the volumes in which they replace each other through a dia¬ 
phragm, is due to the greater facility with which one gas passes 
through a given porous body than another can. But Mr. Gra¬ 
ham caused each gas to pass through a stucco plug into the 
exhausted receiver of an air-pump: and marking the time which 
elapsed before the attached barometer fell two inches (from 29 
to 27), he found that equal volumes of dry air , of air saturated 
with moisture at 60°, of carbonic acid, of azote, and of oxygen, 
entered in 10 f ; of carbonic oxide in 9' 30", of olefiant gas in 
7' 50", of coal gas in 7', and of hydrogen in 4'. Thus, though 
they pass through with different velocities, the expression for 
the rate is very different from that for the volume with which 
they replace each other. Hydrogen, for instance, passes 
through only 2*4 times more rapidly than common air, but its 
diffusion volume is 3*79 times that of air. 
It would be interesting to inquire if the diffusion volumes 
undergo any modification when the diaphragm is formed of dif¬ 
ferent organic products, as in the endosmose experiment of 
Mitchell, who found that when alcohol or aether is separated 
from water by a diaphragm of caoutchouc, the alcohol or aether 
diffuses in greater quantity with the water,—while with a moist 
bladder the water passes through in greater quantity to the 
alcohol. These effects are due to the unequal capillary at¬ 
traction of these substances for the different fluids. 
Condensation of the Gases. —Nieman* has repeated Fara¬ 
day’s experiments on the condensation of the gases with nearly 
the same results. Nitrous oxide, condensed by Faraday with 
a pressure of upwards of fifty atmospheres, he did not succeed 
in reducing to a liquid, while in chlorine and sulphuretted hy¬ 
drogen he found a much higher pressure necessary. Their 
comparative results on these two gases are as follows : 
Chlorine (Faraday) 
Atmosph. 
Sulphuretted hydrogen (Faraday 
) 
4 at 
15-5 C. 
- 
0 
H - 
12*5 
17 — 
12 
54 
0 
58 — 
\2‘5 
* Brandies, Archie, xxxvi. p. 175. 
