Kahlenberg—Osmosis and Osmotic Pressure. 211 
nature to be sure, showing that the hypothesis of van! Hoff 
can not be held and that no special stress is to be laid upon di¬ 
rect measurements of osmotic pressure, which they have conse¬ 
quently not attempted to make. 
In his efforts to measure osmotic pressures directly, Tam- 
mann 1 came to the conclusion that it is not possible to obtain 
reliable, concordant results by means of the method adopted by 
Pfeffer, 2 which he consequently abandoned entirely and turned 
his attention to comparing the osmotic activity of various solu¬ 
tions with one another. Attempts at direct measurements of 
osmotic pressure have again been taken up recently by II. N. 
Morse 3 and his coworkers. They have measured the osmotic 
pressures that are developed when aqueous sugar solutions are 
separated from water by means of precipitated membranes of 
copper ferroeyanide. The method they employed is essentially 
that of Pfeffer, with the exception that they prepared the mem¬ 
branes with the aid of electrolysis. Enough can hardly be said 
in praise of the care and perseverance exercised by Morse and 
his assistants in this work, and yet they have neglected a very 
essential point in their determinations as will appear from con¬ 
siderations given below, and consequently their experiments 
are not conclusive in establishing, as they suppose, that the gas 
laws hold fairly well for the osmotic pressures of aqueous sugar 
solutions,, using copper ferroeyanide membranes. Furthermore, 
attempts to generalize from the data collected by Morse and 
Frazer on aqueous sugar solutions, as to the behavior of all 
solutions taking no consideration of the membranes employed, 
are quite unwarranted. Moreover, while according to the work 
of Morse and Frazer and also according to Flusin 4 the aqueous 
sugar solutions show osmotic pressures in approximate conform¬ 
ity of the gas laws, the Earl of Berkeley and E. G. J. Hartley 5 
have found materially higher pressures than those deduced 
iWied, Ann. 34, 299 (1888). See later attempts by new method Zeit, 
Phys. Chem. 9, 97 (1892). 
2 Pfeffer, be it remembered, worked solely in the interests of physi¬ 
ology and for his special purpose, his experiments were quite sufficient. 
sAmer. Chem Jour. 34, 1 (1905). 
4Compt. Rendus 132, 1110 (1901). 
sProceedings Royal Society (.London), 73, 436 (1904). 
