142 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



Series VIII.* 



The loss in rotation in Series VI amounted to 0.11 per cent and to 0.10 

 per cent in Series VII. There was little prospect of further improve- 

 ment in the manipulation concerned in the closing and opening of the 

 cells, and it was therefore concluded that the continued small dilution 

 of the more concentrated solutions could not be wholly suppressed as 

 long as the rubber stopper was retained as one of the features of the 

 cell. Various devices for closing the cell without it had been studied 

 and more or less tested, but none of them had proved to be entirely 

 practicable except the forerunner of the arrangement seen in Figure 9, 



Table 33. — Cane sugar, Series VIII. Temperature; observed osmotic -pressures; calculated 

 gas pressures of solute; and ratios of osmotic to gas pressures. 



page 19, which was altered and improved until it became satisfactory. 

 The requirements of such a device were that it should permit of a 

 practically instantaneous closing or opening of the cells, and that it 

 should render an enlargement of cell capacity under pressure impossible. 

 In general, it is difficult to meet the second requirement if any rubber 

 whatever is used in closing the cells, and we should have been glad to 

 dispense with that material altogether. But after securely closing a 

 cell, it is necessary to bring upon the contents an initial pressure which 

 is nearly equal to, or even a little above, the osmotic pressure of the 



♦Measurements by H. N. Morse and W. W. Holland. Am. Chem. Jour., xli, 257. 



