2 Mr. P. S. Barlow : Osmotic Experiments 



pressure o£ the solvent and dissolved substance acting on a 

 diaphragm, which, being permeable to the solvent only, 

 renders the pressure of the dissolved substance inoperative, 

 and hence causes the total operative pressure of the solution 

 to be that of only the solvent present in it. Now, I have shown 

 that if we take a solution such as that of propyl alcohol in 

 water, and place it in a semipermeable vessel surrounded by 

 water, the latter will pass through towards the solution, 

 ergo, the vessel is permeable to water but impermeable to 

 the alcohol ; but if the same vessel with its same contents is 

 surrounded by propyl alcohol, it is the alcohol that passes 

 through towards the solution, ergo, the vessel is permeable to 



the alcohol, but not to the water The obvious 



conclusion to draw from this experiment is, that it is the 

 solution, and not either of the substances separately, to which 

 the membrane is impermeable, and this is just what we should 

 anticipate on the hydrate theory, the molecules of hydrates 

 being necessarily larger than those of their constituents.'' 

 The experiment is thus accepted as a c crucial' one. 



The experimental work, of which a short account is given 

 in this paper, shows that the observation of an increase in the 

 osmotic pressure after the cell is placed in the alcohol is 

 correct, but that it is not due to an inflow of alcohol. Had 

 more time been given to the experiment, it would have been 

 found that this increase is not permanent as when the cell is 

 in water. The permanent result is an outflow from the cell 

 into the alcohol. And further : had the cell containing the 

 solution been placed by Pickering again in water, he would 

 most likely have found a decrease in pressure; and obviously 

 the outflow causing it would have been the reverse of the 

 anticipation based on the hydrate theory as above quoted. 

 The explanation of what are here called " temporary " rise 

 and fall (or inflow and outflow) is given after some account 

 of the experiments. 



The Cells. 



It is not intended to give here a full account of the pre- 

 paration of the cells. This was by far the most tedious part 

 of the work. That some cells should prove useful and others 

 prove failures, after exactly the same treatment, seems 

 only to be accounted for by the presence of flaws within the 

 pot. The membrane used was that of copper ferrocyanide 

 obtained by diffusion. Of the thirty-one cells used in the 

 preparation, fifteen proved sound. Of the others, their failure 



