EXPERIMENTAL WORK ON OSMOTIC PRESSURE 623 



The time necessary for a solution to develop its maximum 

 osmotic pressure appears to vary very considerably with the 

 membrane employed. This is especially the case when the 

 osmotic pressure is measured by the manometer method, as 

 employed by Messrs. Morse and Frazer. These workers speak 

 of one cell in which the maximum pressure was usually developed 

 within seven hours, and of two other cells for which over forty 

 hours were similarly required. It is noteworthy that these 

 times appear to be independent of the concentration of the 

 solution in the cell. In the method of measuring osmotic 

 pressure adopted by Lord Berkeley and Mr. Hartley, the time 

 required for the actual measurement is shorter and more 

 uniformly independent of the particular membrane employed. 

 In only a few cases was the membrane kept under pressure for 

 more than seven hours, while in many experiments a much 

 shorter time was found sufficient. 



The results obtained for the osmotic pressures of cane sugar 

 solutions by Messrs. Morse and Frazer on the one hand, and 

 by Lord Berkeley and Mr. Hartley on the other, are not directly 

 comparable, for two reasons. In the first place, the measure- 

 ments of Messrs. Morse and Frazer were made at temperatures 

 of 20 to 24 C, whilst those of Lord Berkeley and Mr. Hartley 

 were carried out at o° C. In the second place, the ranges of 

 concentration differ in the two cases, for the solutions examined 

 by Messrs. Morse and Frazer were between o*i normal and 

 0*82 normal, while the range of concentration of those examined 

 by Lord Berkeley and Mr. Hartley was 0^27-2-2 normal, and 

 only one of the latter solutions falls within the range of con- 

 centration covered by Messrs. Morse and Frazer's experiments. 

 An idea of the magnitude of the osmotic pressures of the various 

 solutions may be best gained by a glance at the following tables. 

 Table I. gives a summary of Messrs. Morse and Frazer's results, 

 Table II. a summary of Lord Berkeley and Mr. Hartley's results : 



Table I 



Gram molecules of cane 



sugar per litre of 



solution. 



0"098 



0-192 



0-369 



0533 

 0-684 

 - 82S 



Osmotic pressure in 

 atmospheres. 



2"53 



477 

 9-66 



1474 

 I9"34 

 24-23 



Table II 



Gram molecules of cane 



sugar per litre of 



solution. 



0-527 



0-877 



1*23 



I- 5 8 



i*93 



2'19 



Osmotic pressure in 

 atmospheres. 



i3"95 

 2677 



43'97 



67-51 

 10078 

 13374 



