Fluctuating or Alternating Hydration Effects. 85 



previous one, and the experiment was discontinued after a total period 

 of 100 hours. 



The use of hundredth-normal potassium nitrate-citric acid as the first 

 solution caused a swelling of 708 per cent in 7 hours, at which time 

 the rate of increase was very slow and would not have carried the 

 thickness to more than 800 per cent of the original. Replacement of 

 the acidified salt by the salt alone in the same concentration and its 

 renewal accelerated imbibition, which proceeded at a rate which les- 

 sened very slowly for 63 hours. The sweUing was at first at the rate 

 of 100 per cent in 4 hours and about 25 per cent during the last 4 hours. 

 The increase during this period of 87 hours was about 700 per cent, 

 making the total increase over 1,400 per cent. The behavior of the 

 colloid during this period was that of a plant with diminishing acidity. 



The salt was now pipetted off and replaced with distilled water which 

 was renewed. The acceleration following was so abrupt that the rate 

 jumped from 25 per cent in 4 hoxu-s to 750 per cent in 2 hours. The 

 swelling at the end of 24 hours was 1,778 per cent, at which time in- 

 crease was still in progress. The total increase now amounted to 3,195 

 per cent. The unsatisfied capacity would have doubtless carried the 

 swelling to a thickness as great as any yet observed in any of the bio- 

 colloids and in excess of the sections which were swelled initially in the 

 salt alone. 



The mass was now nearly 97 per cent water. Replacement of the 

 water by acidified salt solution was followed by a shrinkage of about 

 200 per cent of the original thickness of the sections in 8 hours. When 

 this was washed out, the loss was regained in a few hours. These 

 sections were now set aside for desiccation. The final period of 16 

 hours in the swelling was in distilled water, so that the acidified potas- 

 siimi nitrate in which the sections had been immersed for the preceding 

 8 hours must have been reduced to a very small amount. 



The last desiccation had left the sections warped to some extent, 

 which interfered with accurate remeasurements, but the thickness had 

 been reduced from 0.18 to 0.16 mm. and even thinner. The irregulari- 

 ties of course operated to introduce some error in the swelling, which 

 would make the total appear to be 100 to 200 per cent less than it 

 should be. 



The swelhng in distilled water at 18° to 20° C. now progressed over 

 a period of about 96 hours, reaching a total of 1,625 per cent. Both 

 the amount of the total and the length of time necessary to reach full 

 capacity would indicate that the sections still contained some of the 

 protein or its derivatives and perhaps some of the salts. Agar alone 

 would attain full capacity at a lesser volume and in a shorter time. 



A second set of sections of agar 90 and oat protein 10 parts were 

 first treated with acidified potassium nitrate, in which the swelling was 

 about 500 per cent (the solution being freshly made) in 16 hours. This 



