212 Wisconsin Academy of Sciences, Arts and Letters. 
from the gas law, even though their membranes, which were 
also prepared with the aid of electrolysis, were admittedly not 
perfectly tight. 
Among the many opponents of the van’t Hoff theory of os¬ 
mosis may be mentioned Lothar Meyer, Raoult, Fitzgerald, 
Pickering, Quincke, Dieterici, J. Traube, Battelli and Stephan- 
ini. The opponents of the van’t Hoff idea have generally held 
that the so-called osmotic pressure is an ordinary hydrostatic 
pressure brought about by entrance of liquid into the osmotic 
cell. Concerning the reason for this entrance of additional 
liquid into the osmotic cell there has, however, been difference 
of opinion; some holding that it is due to attraction that is es¬ 
sentially chemical in character; others that it is due to capillar¬ 
ity; and still others that it is caused by surface tension. The 
latter view has lately been prominently brought forth by 
Traube, 1 whose claim is that ‘ ‘ The difference in surface tensions 
determines the direction and velocity of the osmosis.’’ His idea 
is that the main direction of osmosis is always toward the liquid 
having the greater surface tension. Again, Battelli and Ste- 
phanini 2 also express the opinion that difference in surface ten¬ 
sion is the cause of osmosis. But on the basis of their experi¬ 
mental work, they modify Traube’s contention to the effect that 
the main osmotic current is not always toward the liquid of 
higher surface tension, but that the process always proceeds in 
such a direction as to tend to equalize the surface tensions of 
the liquids on the opposite sides of the septum. Very recently 
Barlow 3 has also brought forward cases which are not in har¬ 
mony with the theory of Traube. 
In the present investigation the main purpose has been to 
inquire into the nature of osmosis and osmotic pressure, and to 
test whether the latter really follows the gas laws. To this end 
a considerable number of osmotic experiments were performed 
in 'which liquids of similar and also of very different character 
were separated from each other by different membranes. In 
this work observations were taken as to the direction of osmosis 
with change of membrane, with change of solvent and also with 
lPhil. Mag. (6) 8, 704 (1904). 
2Atti della Reale Accademia dei Lincei 14, 3 (1905). 
3Phil. Mag. (6) 10, (1905). 
