Kohlenberg—Osmosis and Osmotic Pressure. 223 
branes used could be perfectly securely tied. Very many 
evenly applied turns of a stout, moderately fine, white cotton 
thread were wound on after the membrane had been care¬ 
fully placed in position over the mouth of the tube. This part 
of the work required much time, patience and perseverance, 
as well as skill and practice. After thus securing the mem¬ 
brane over the mouth of the thistle tube, the latter was filled 
with one of the liquids to a point slightly above the bell of the 
tube, which was then immersed in a beaker containing the 
other liquid. The level of the two liquids was, of course, the 
same to begin with. 
For convenience in future reference the experiments per¬ 
formed have been numbered. The liquid in the bell of the 
osmometer will always be called the inner or inside liquid; that 
in the beaker, the outer or outside liquid. 
1) The membrane consisted of sheet rubber, vulcanized 
caoutchouc, such as is used by dentists in making their “ rubber 
dam. 77 This rubber was very elastic, being almost the pure 
gum. It could readily be stretched over the osmometer and 
tied on so as to form a perfect joint, for all folds could be 
avoided. The inside liquid was a 20 per cent aqueous cane 
sugar solution; the outside liquid was pure water. The ex¬ 
periment ran 48 hours. No change took place. The liquids 
remained at the same level and no sugar passed through the 
membrane into the water on the outside. 
2) A rubber membrane was used as before. The inside 
liquid consisted of a 20 per cent aqueous NaCl solution, the 
outside liquid of pure water. No change took place, the 
liquids remaining on the same level and not a trace of salt 
appearing in the water without. When the outside water was 
replaced with toluene, the latter caused the rubber to swell, 
but no salt or water passed into the toluene, neither did the 
toluene ~ go into the brine. On afterward exposing the mem¬ 
brane to the air, it lost its toluene content and shrank to its 
former size, remaining throughout quite elastic. 
Experiments 1 and 2 show that it is possible to get the joint 
between rubber and glass perfectly tight. It is perfectly clear 
that no change took place when water and the aqueous solu- 
