

376 



BOTANICAL GAZETTE 



[may 



i 



calibrated by weighing with mercury. One scale division on G 

 0.000337 gm. of water at 25 C. The whole apparatus is then 

 immersed in a vessel containing a solution of cane sugar or sodium 

 chloride and the vessel placed in a water bath regulated to constant 

 temperature. The osmotic force of the bathing solution pulls 

 water through the membrane from the internal chamber, and this 

 causes the meniscus in the capillary tube to recede. By successive 



j ' * 1 ( 1 1 i n 



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Fig. 2.— Drawing of osmometer: explanation in text 



readings of the position of the meniscus in G at various intervals 



of time the ru 

 be determined. 



movement through the membrane can 



As water passes through the membrane, it has a tendency to 

 dilute the bathing solution at K. This tendency is overcome by a 

 stirrer whirling in front of the membrane at K which keeps the 

 concentration constant there. The amount of water passing into 

 the bathing solution is so small as compared with the large volume 

 of the latter that the concentration of the solution exerting the 

 osmotic pull is maintained constant. 



