Water Deficit or Unsatisfied Hydration Capacity. 101 



It is to be added that when the dried slices of the commercial prep- 

 aration of potatoes known as "Anhydrous" were tested at 22° to 23° 

 C, the sections, which were 1 to 1.1 mm. in thickness, showed a 

 maximum swelling of 265 per cent in potassium hydroxid 0.01 M, 

 250 per cent in citric acid (0.01 N), and 200 per cent in acidified 

 potassium chloride, at 0.01 N concentration, while the swelling in dis- 

 tilled water was 222 per cent. The relatively lessened swelling in 

 distilled water, as compared with salts and acids, might be attributed to 

 the elimination of the osmotic action of the semi-permeable membrane. 

 The exact history of the preparation of the material is not available, 

 however, and here, as in other dried material, the coagulatory effects 

 of contained salts and acids in desiccation must be taken into account. 

 This will become apparent from the results obtained from the swelling 

 of dried apples made from machine-cut strips. Sections cut, from 

 these strips had an average thickness of 2.6 to 3.4 mm. and gave 

 swelling increases as follows at 16° to 18° C. : 



Table 80. 



p. ct. 



Distilled water 72 



Citric acid, 0.01 N 69 



Sodium hydroxid 0.01 M 105 



Calcium chloride, 3 M 123 



The expected proportionate swellings in water, acids, and alkaline 

 solutions are noted, but the great imbibition from the solution of 

 calcium chloride which would afford an osmotic pressure of 68 atmos- 

 pheres is a fact of extraordinary interest. An extension of the test 

 was made in different concentrations of this salt, in which it was found 

 that at 19° to 20° C, swellings of 82 and 95 per cent only were obtained 

 in a solution of 0.01 M and in other tests of the original concentrated 

 solution; 3 M gave an increase of 230 per cent on one trial and 106 

 per cent on another at the above temperatures. This maximum was 

 obtained from sections 1 mm. in thickness, and it is suggested that 

 they were in a state of undue compression. Similar sections swelled 

 180 per cent in a 2.7 M solution of potassium nitrate capable of exert- 

 ing an osmotic pull of 84 atmospheres.^ Thicker sections in the potas- 

 sium solutions of this concentration swelled only 62 per cent and gave 

 an expected greater swelling of 94 per cent in a 0.01 N solution. The 

 maximum swelling in the concentrated calcium solution suggests that 

 compounds of the calcium with the pectin may be formed of higher 

 hydration value, which makes possible these imexpected imbibition 

 reactions. Such swellings, however, have been found in the case of 

 colloidal mixtures which simulate the action of the plant in concen- 

 trated solutions of potassium nitrate. 



^ MacDougal and Spoehr, The behavior of certain gels useful in the interpretation of the ac- 

 tion of plants. Science, 45:484-488. 1916. 



