220 Wisconsin Academy of Sciences, Arts and Letters . 
reform is water, D. At E there is a cork collar which holds 
the tube in place. This collar does not fit perfectly tight, yet 
it minimizes the evaporation of the ether. The cork E is rather 
loosely inserted; its purpose is simply to prevent undue evap¬ 
oration. This was also the purpose of the layer of water, D, 
which to be sure also kept the chloroform saturated with water. 
Both the ether and chloroform used were saturated with water 
to begin with as in the previous case. With this arrangement 
the layer C increased in bulk, the column rising until the layer 
D touched the cork E. The experiment was continued for two 
weeks, the cork at A being rather thick caused the change to 
progress slowly. 1 
This case of ether, water, chloroform, Fig. 1, has been thus 
described in detail because it illustrates all the essential points 
to be taken into consideration in the study of the osmotic pro¬ 
cess. We have seen what conditions are necessary for the 
process to proceed at all, what are the various factors that 
modify the rate of the change, and what causes the so-called 
osmotic pressure. It has further been shown under what con¬ 
ditions we get a so-called semi-permeable membrane, and it is 
evident that an absolutely semi-permeable membrane exists only 
in theory. On the basis of his elaborate experimental re¬ 
searches, Quincke 2 has also arrived at this conclusion. He 
stoutly contends that there really is no such a thing as a semi- 
permeable membrane and that a theory which postulates such 
can not be maintained. His words are, ‘ ‘ Ich bestreite, dass eine 
halb durchlassige Miembran existirt, Hamit fallt aber auch der 
osmotische Druck, dessen Theorie die Existenz einer halbdureh- 
lassigen Membran voraussetzt.As stated above, there is in 
general always an outflow from an osmotic cell as well as an 
inflow, and when the former is extremely slight as compared 
with the latter, the membrane is called semi-permeable; but com¬ 
monly the outflow is quite sufficient to demand consideration. 
At any rate, the osmotic pressure is always the resultant of in¬ 
flow and outflow caused by the attractions that come into play, 
i Compare in this connection a similar experiment of Nernst, Zeit. 
Phys. Chem. 6, 35 (1890). 
2Drude’s Ann. 7, 682 (1902). 
