KaJilenberg—Osmosis and Osmotic Pressure. 221 
which attractions are to the mind of the writer the same as 
what is commonly called chemical affinity, and consequently 
such so-called osmotic pressures may under suitable conditions 
be very great indeed, while under other conditions they may 
be quite small. They would, moreover, present considerable 
variation according to the nature of the substances employed. 
No originality is claimed for the ether, water, chloroform ex¬ 
periment, Fig. 1. It occurred to me after a goodly number 
of the experiments described below had been performed; but in 
looking over the earlier articles of the rather voluminous litera¬ 
ture on the subject of osmosis, I found that in 1854 L’Hermite 
(Compt. rend. 39,1177) described the experiment in question. 
His statements concerning its import and bearing are very 
clear, though, of course, he does not speak of semi-permeable 
membranes and osmotic pressures, for these concepts were at 
that time quite unknown. A reference to the article of 
L’Hermite is also made in the bibliography in Lehmann’s Mo- 
lekularphysik. 
However, after having L’Hermite’s experiment clearly before 
me, the principles it illustrates soon became the guide in future 
experimentation, for they enabled me to foretell whether a 
membrane would be permeable or impermeable for a certain sub¬ 
stance under given conditons; and if permeable for several 
substances, which of these would go through most readily. 1 
was thus enabled to forecast in which direction the main os¬ 
motic current would go. These matters were not only of con¬ 
sequence in direct measurements of osmotic pressures, detailed 
below, but they were also of importance in dialysis as will ap¬ 
pear farther on. Again, by demonstrating the nature of the 
process, it clearly appeared that in determining the maximum 
osmotic pressure the contents of the osmotic cell must be con¬ 
tinually stirred. For, taking the arrangement as given in Fig. 
1 and again imagining the aqueous layer B as quasi solid and 
firmly fixed in place, it is evident that as ether is drawn into 
compartment A, the liquid in that compartment becomes en¬ 
riched with ether just where it touches B, and that consequently 
the osmotic pressure set up in A is not as great as it would be 
if the liquid in A were continually stirred so as to rapidly dis- 
