230 Wisconsin Academy of Sciences, Arts and Letters. 
19) The inside liquid was 0.1 normal solution of AgN0 3 
in pyridine, the outside liquid pyridine and the septum rubber. 
The liquid rose slowly in the osmometer, indicating the direc¬ 
tion of the main current to be from the pyridine through the 
rubber to the solution. An examination of the outer liquid 
showed the presence of only a very small amount of nitrate of 
silver. The experiment was repeated using a much heavier 
piece or ordinary gray sheet india rubber as a septum, with the 
same result. And again, it was repeated using the rubber dam 
as a membrane once more, but supporting it by tying over the 
outside of it a piece of muslin. With this arrangement the 
liquid rose in the stem of the thistle tube to a height of 28.5 
cm. in 18 days, remaining there constant for two days, and 
then receding slightly. The temperature was very nearly 17 
degrees throughout the test. The outer liquid was found to 
contain appreciable amounts of AgN0 3 , but hardly an estima¬ 
ble quantity. This shows that vulcanized caoutchouc is prac¬ 
tically impermeable for AgN0 3 under the conditions described; 
in other words that it is a “semi-permeable” membrane. 
20) The inner liquid was a 0.05 normal solution of AgN0 3 
in pyridine, the outer pyridine, and the septum rubber. At 
17° C. no change whatever was observed after 6 days. After 
19 days a rise of about 0.5 cm. of the liquid in the stem of the 
osmometer was observed. The outer liquid was then analyzed 
for silver nitrate. Only traces were found, not an estimable 
quantity. This shows that the membrane did not leak and 
that the so-called osmotic pressure of a AgN0 3 solution in 
pyridine which is 0.05 normal is practically nil at 17° C. when 
vulcanized caoutchouc is used as the semi-permeable membrane. 
21 ) The inner liquid was a normal solution of AgN0 3 in 
pyridine, the outer liquid pyridine, and the membrane rubber. 
The apparatus was kept at a temperature which varied grad¬ 
ually between —16° and —15° C. At the end of the second 
day the liquid in the osmometer had risen to a height of 7.2 
cm., the temperature being —16.° At the end of the third 
day the height of the column was 15.6 cm., the temperature 
being _15.° The membrane was intact and but traces of 
silver were present in the outer liquids. 
