1904.] Method of Measuring High Osmotic Pressures. 



437 



litre, gave an osmotic pressure of 8" 13 atmospheres, the theoretical 

 value, derived from the gas laws, is 7*89. 



This apparatus was discarded, and attempts were made to determine 

 osmotic pressures in a quicker way by a method somewhat similar to 

 that which Tammann* tried, i.e., by directly applying to the solution 

 a gradually increasing pressure until the osmotic pressure has been 

 reached, and meanwhile noting the change in the volume of the 

 solvent. We replaced the two glass globes by iron cylinders, and 

 connected one of them, B, which was filled with the solution, to a 



Fig. 1. 



Rubber 



powerful pressure apparatus. Water filled the other, A, and also a 

 graduated glass capillary, connected to A by a perforated rubber 

 stopper. Pressure was applied to the solution and the rate at which 

 the water rose in the capillary was noted. The rate was found to be, 

 apparently, slightly different before the osmotic pressure had been 

 reached to that which it was after that pressure had been passed. The 

 phenomenon w T as so complicated, however, by the volume effect due to 

 the compression of the washers placed on either side of the plate, that 

 no very clear results could be obtained. 



* a. Tammann, « Zeit. f. Plays. Claem.,' vol. 9, p. 97. 



