Kahlenberg—Osmosis and Osmotic Pressure. 231 
22 ) The inner liquid was normal solution of AgNO s in 
pyridine, the outer liquid pyridine, and the membrane rubber. 
In this ease a piece of common vulcanized rubber about 1 mm. 
thick such as is used on footpower laboratory bellows was em¬ 
ployed. It was supported on each side by pieces of muslin and 
perforated steel discs, and the whole was then securely screwed 
to the lower end of an osmotic cell made of steel. The maxi¬ 
mum pressure which was read on a closed manometer, using 
mercury between the air space and the inner liquid was 14.95 
atmospheres at 20° C. The membrane did not “leak,” which 
was evident from the fact that only mere traces of AgNO s 
were found in the outer liquid,, though the experiment was run 
for two weeks, the pressure remaining practically constant for 
five days. This steel osmotic cell consumed considerable time 
in its construction, and many difficulties had to be overcome in 
perfecting it and attaching the manometer to it. However, it 
is unnecessary to enter into a detailed description of the cell, 
since no special significance will be attached to the single re¬ 
sult recorded here, it being given simply to show that a very 
considerable pressure may be produced by a normal solution of 
AgNO s in pyridine when it is separated from pure pyridine 
by vulcanized caoutchouc at 20°, whereas at —16° (No. 21) 
the pressure formed is practically insignificant. 
Silver nitrate is insoluble in hydrocarbons, which shows that 
the affinity between that salt and hydrocarbons is slight. Now 
as caoutchouc is a hydrocarbon substance, the affinity between 
it and silver nitrate would be slight. Pyridine has consider¬ 
able affinity for silver nitrate. It dissolves the salt readily 
with evolution of a considerable amount of heat. Pyridine is 
soluble in all proportions in hydrocarbons—is consequently 
readily imbibed by rubber. When a silver nitrate solution in 
pyridine is placed in contact with rubber, the latter soaks up 
pyridine, but also some silver nitrate with it, since the pyridine 
and the salt are bound to each other by mutual attraction. 
This accounts for the fact that traces of silver nitrate pass 
into the pyridine when it is separated from a silver nitrate so¬ 
lution in pyridine by means of a rubber septum as in experi¬ 
ments 19, 20, 21 and 22, though the main current is that of the 
