1917] 



DEXX I —PERM E A BILI T 1 



r 



377 



I 



At the end of an experiment it is possible to record the quantity 

 of water passing through a known area of membrane, in a known 

 interval of time, at a constant known temperature, and under the 



constant osmotic 



pull of a solution whose osmotic pressure in 

 atmospheres is known. This gives a measure of the permeability 

 of the membrane under the conditions of the experiment. 



The sources of error and the precautions taken were as follows : 



Temperature 

 ; immersed i 



— It was found that when the apparatus 



minutes. An interval of at least 10 minutes was 



allowed before readings were begun. 



The temperature of the 

 bathing solution was constant to =±=o?i C. The effect of the 

 possible deviation of the temperature of the internal liquid upon 

 the readings of the meniscus in the side arm was calculated. 1 The 

 volume of the osmometer is 4421 .13 cu. mm. Assuming it filled 

 with water at 4 C, then changes in temperature of o?i show the 

 relation between temperature errors and scale division of the 

 osmometer as indicated in table I. 



Temperature 



TABLE I 



Volume error 

 (in mg.) of water 



i5°*o?i 

 2 5 °*o?i 

 35° *=o? 1 

 45° ±0° 1 



0.01326 

 0.17665 

 0.18525 

 0.30764 

 0.37212 



Scale division 



value (in mg.) 



of water 



Error of readings 

 in scale divisions 



II 



arm 



scale division. Temperature deviation therefore introduced no 



error resulted. 



temperature 



Variation in membranes.— It was early found that there was 



a lar 



same species. 



permeability of different 



membran 



but only with itself under the various conditions of the experiment. 



1 Calculated from data taken from Smithsonian tables, Smithsonian Misc. 

 Coll. 63: no. 6. 



