Kahlenberg—Osmosis and Osmotic Pressure. 227 
rection opposite to that of the major; in other words, that when 
caoutchouc is the membrane and ether is going into the alcohol 
there is also some alcohol passing into the ether; and when 
the bladder is employed, there is some ether passing into the 
alcohol, though the main current is from the alcohol to the 
ether. Raoult was, however, perfectly clear in his own mind 
with regard to this matter as will appear from a quotation from 
a letter written by him printed below. | 
It is hardly necessary to add that in the light of what has 
already been said above, the results obtained by Raoult and 
Flusin are exactly such as might have been foreseen. 1 
9) The inner liquid was glacial acetic acid, the outer liquid 
distilled water and the membrane rubber. Within five minutes 
blue litmus paper placed in the water turned red, showing that 
the acid was passing through the rubber. This was the direc¬ 
tion of the main current, which might have been expected*, 
since glacial acetic acid is more readily absorbed by rubber 
than is water. 
10) The inner liquid was a 10 per cent solution of acetic 
acid in water, the outer liquid water, and the membrane rubber. 
After 1.5 hours, the blue litmus in the water began to turn red, 
indicating that in this case, too, the acid was passing through the 
rubber into the water. The direction of the main current then 
was not altered by diluting the acetic acid considerably with 
water, which result is in line with what Raoult found in the 
ether—methyl alcohol experiment referred to above. 
11) The inner liquid was a strong solution of trichloracetic 
acid in water, the outer liquid water and the septum rubber. 
But very little acid passed through the rubber into the water. 
Hardly any change took place in the 20 hours during which 
the experiment was continued. 
12) The inside liquid was a solution of trichloracetic acid 
in benzene, the outside liquid water and the membrane rubber. 
In this case acid went into the water in very considerable quan¬ 
tity. This was the direction of the main current. The ex¬ 
periment was run for 20 hours. 
i Compare also the remarks by Tammann, Zeit. Phys. Chem. 22 ], 
490 (1897). 
