Fluctuating or Alternating Hydration Effects. 



79 



An experiment of this kind was carried out July 30 to August 9, 

 1917, in the equable-temperature chambers of the Coastal Laboratory 

 at 15° to 16° C, in which sections composed of 9 parts agar and 1 part 

 bean protein were subjected to alternating action of acids and hydro- 

 xid after they had first been swelled in water for 5 hours. Citric, malic, 

 and formic acids were used in separate sets at hundredth-normal con- 

 centration, but no determination was made of the hydrogen-ion con- 

 centration, and as the initial swellings in water were widely divergent, 

 the final totals have no especial significance, entire interest lying in the 

 changes in volume resulting from the replacements. (See fig. 11.) 



I?p.m. m. I?p.m. m. 12p.m. m. 12p.m. m. 12p.m. m. 12p.m. en. 12p.m. 



Fig. 11. — Record of variations in thickness of sections of agar and bean protein subjected to the 

 action of water, acids, and alkalies, as described in text pages 79 and 80. 



Trios of sections which were 0.25 mm. in thickness were placed in 

 dishes into which distilled water was poured in the usual manner. 

 At the end of 5 hours, designated as A on the tracing, the water was 

 drawn off by a pipette and a solution of hundredth-normal sodium 

 hydroxid substituted, which was followed by an expansion which 

 reached almost to the possible total of 580 to 860 per cent of . the 

 original dried sections in 8 hours. At the end of this time the sections 

 were in an advanced stage of hydration and were also probably 

 impregnated with salts formed by potassium with the carbohydrates 

 and proteins in the gel, and the possible presence of these compounds 

 as modified by subsequent experiences must be kept in mind. 



The three acids were now added to the separate sets of sections, 

 and from this point their experiences diverge. All agreed in under- 

 going a retraction during the next 9 hours which was most pro- 

 nounced in the citric acid. Shrinkage at a slow rate was still in prog- 

 ress at the end of this period, B, when the acid solutions were removed 

 and distilled water substituted. No effort was made to wash the 

 sections which were saturated with the acid and salt, and the operation 

 resulted simply in a reduced acidity in which some slight swelling took 

 place during the 5 hours ending at C, at which time the reaction was 

 practically at an end. 



The hydroxid was now used for the second time, replacing the acid, 

 for 2 hours, in which time a further slight swelling ensued. Acids 



