JACQUES LOEB 



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The next question was: What is the origin of the p.d.? It occurred 

 to the writer that a measurement of the hydrogen ion concentration 

 inside and outside after 1 hour might possibly throw a light on this 

 problem. The results of these measurements are plotted in Fig. 4, 

 The reader will remember that at the beginning the hydrogen ion 

 concentration was the same inside and outside. Yet after 1 hour 



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pH L8 ZO 22. 2.4 a6 2.8 3.0 3.2 3.4 36 38 4.0 42 44 4.6 48 5.0 52 



Fig. 4. Abscissae are the initial pH; ordinates, the values (pH inside minus 

 pH outside) in preceding experiment. Attention is called to the similarity of 

 the curves in Figs. 3 and 4, 



(and in fact much earlier) it is obvious that some of the acid has 

 diffused from the inside into the outside solution so that the hydrogen 

 ion concentration is higher outside than inside the collodion bag 

 containing the salt solution. 



This then leads to the result that when we separate identical acid 

 solutions by a collodion membrane coated with a film of gelatin, and 

 put inside the collodion bag a solution of a neutral salt with a mono- 



