212 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



mained in the bath 17 days, and the highest osmotic pressure exhibited 

 by the solution during this time was 18.579 atmospheres. In general, 

 the pressure showed a tendency to decline, and on the seventeenth day 

 it had fallen to 17.407 atmospheres. 



In the third trial the cell was soaked in water 8 days and then set up, 

 as on previous occasions, with a 0.5 weight-normal solution of potassium 

 chloride. It remained in the bath 15 days. The highest osmotic 

 pressure observed was 12.515. On the fifteenth day, the pressure had 

 declined to 10.386 atmospheres. 



The membrane had no doubt suffered severely in contact with the 

 potassium chloride. The nature of the injury is, of course, indetermin- 

 able; but the conduct of the copper ferrocyanide membrane in the pres- 

 ence of this electrolyte resembles that of the zinc ferrocyanide mem- 

 brane in contact with either water or a solution of a non-electrolyte. 



Experiment 2. 



Another cell, which had also made a long and uniformly good record 

 with non-electrolytes, was set up at 30° with a 0.5 weight-normal solu- 

 tion of potassium chloride and allowed to remain in the bath 36 days. 

 The osmotic pressure which it should have developed, according to 

 the record of the cell used in experiment 1, was about 20.6 atmospheres; 

 the highest observed pressure was 18.567 atmospheres. On the thirty- 

 sixth day, the osmotic pressure had fallen to 17.628 atmospheres. 



The same cell was soaked in water for 20 days and set up again under the 

 same conditions as before. It remained in the bath 24 days. The highest 

 osmotic pressure exhibited by the solution was 16.695 atmospheres. The 

 pressure on the twenty-fourth day was 16.299 atmospheres. 



The pressure on the first trial was greater in experiment 1 than in 

 experiment 2, showing that the membrane in the former case was 

 originally the better of the two ; but the deterioration at the end of the 

 second trial was relatively less in experiment 2 than in experiment 1. 

 This was probably due to the much longer soaking in water between 

 trials which was given to the membrane in the second cell. 



Eight other experiments, in most respects similar to experiments 1 

 and 2, were carried out with cells whose excellence for the measurement 

 of the osmotic pressure of non-electrolytes had been fully demonstrated, 

 but as no further light was obtained through them, as to the action of 

 electrolytes on the membrane, they are omitted. The results were all 

 confirmatory of the observations made in experiments 1 and 2, and to 

 the effect that the copper ferrocyanide membrane suffers severely in 

 the presence of potassium chloride. The question, whether the ten 

 membranes which have been injured by this electrolyte can be restored 

 to usefulness by long-continued soaking in water, is still to be answered. 



Two experiments were made with 0.5 weight-normal solutions of 

 barium chloride, but the results were as unsatisfactory as had been those 

 with potassium chloride. 



