Osmosis. 



To secure the manifestation of osmotic pressure with 

 this apparatus there is developed, on the inner wall of the 

 porous porcelain cell, a precipitation membrane which is 

 impervious to the solution whose pressure is to be 

 measured but which is readily permeable by water, placed 

 in the outer vessel. The function of the porous cell is 

 to act as a strong framework capable of permitting the 

 precipitation membrane to withstand the pressure de- 

 veloped without a sensible increase in the volume of the 

 cell taking place. When the pressure-producing fluid is 

 placed on the inside and the apparatus is placed in water 

 the case becomes analogous to the left diagram of Fig. 6, 

 except that the wall is now incapable of expansion and the 

 pressure becomes manifest through the rise of mercury in 

 the pressure gage.* 



61. Osmotic Pressure of Cane Sugar Pfeffer, working 

 with, his apparatus and different strengths of cane sugar 

 in solution on the inside, was able to show that pressures 

 were developed having the intensities indicated in the table 

 below : 



Table showing osmotic pressure of solutions of cane sugar of 

 different degrees of concentration. 



From this table it appears that Pfeffer was able to 

 secure pressures ranging from about 10 to CO pounds per 

 square inch, or enough to sustain a column of water from 

 24 to 137 feet high. 



* Detailed descriptions of the method of forming the membrane 

 and setting up the apparatus can be found in Gray's Botanical Text 

 Book, 6th Ed., Vol. II, p. 1:27, and in Jones' The Modern Theory cf 

 Solutions, p. 3. 



