4 Mr. P. S. Barlow : Osmotic Experiments 



relieve slowly any pressure set up during an experiment. 

 The volume of the air enclosed within the cell was very small,, 

 so that any change in the volume o£ the cell's contents 

 immediately moved the gauge-level. The bore of the gauge- 

 tubing was small, in the largest having a volume of '0358 c.c. 

 per cm. length. 



The Experiments. 



In the experiments with the alcohol solutions, no attempt 

 was made to get the actual values of the osmotic pressures. 

 In most cases, the solutions were too strong and generally the 

 pressure was not allowed to reach values greater than those 

 for which the cell had previously been tested, thus keeping 

 the experiment within the known limits of the cell's strength. 

 However, in more than one case, a cell left overnight got up 

 a pressure large enough to burst the rubber tubing or force 

 it over the flange, below which it was wired. The cells still 

 remained sound. What pressure the best cells could bear 

 before breaking down is not known ; and for obvious reasons 

 it has not been sought. 



Experiments were performed with varying strengths of 

 solutions, going up from 15 per cent, alcohol by steps of 

 5 per cent, to 70 per cent. Strengths below and above these 

 limits were also used, all with the same result. This gradual 

 increase of the strength of the solution was thought to be 

 advisable, because it seemed not unlikely that when the 

 alcohol was in great excess the sign of the osmotic current 

 might change. In other words, the alcohol might become 

 the solvent and the water the solute. This, however, was 

 not found even when the water was present in very small 

 quantity indeed. 



In these experiments, where water was always present, the 

 alcohols were not further rectified. They were supplied to 

 the laboratory as pure and so used. The specific gravity 

 (compared to water at 4° C.) of the ethyl alcohol was *7948 

 at 16° C. ; that of the methyl alcohol, '7940 at 18° C; that 

 of the propyl alcohol, '8274 at 14°'8 C. This last was taken 

 some time after the experiments were completed, and is there- 

 fore likely to be much higher than when first used. 



On removing from one liquid to another, the cells were 

 dried by folding in filter-paper. 



