74 CARNEGIE INSTITUTION OF WASHINGTON. 



calculations have been based upon the ratios of maximum vapor 

 pressures of water in the air at 20° C. to the corresponding pressures 

 at other required temperatures; consequently, no inconvenience is 

 caused, especially as it has already been proved that the tripartite 

 slips may be standardized in the laboratory and used in the field 

 months or years later. 



Investigations on the Imbibition of Water by Gelatine, by Edith B. Shreve. 



EFFECT OF INCLUDING VARIOUS SOLUTIONS WITHIN GELATINE JELLY, 



It was noted in the report of last year* that when gelatine is soaked 

 in M/2 and M/4 solutions of sodium sulphate, sodium citrate, or 

 sodium tartrate for several hours, heated to 60° C, and then allowed 

 to cool, the resulting jellies absorb distilled water at a faster rate 

 than does a jelly of the same water-content made with distilled water. 

 Hofmeister and others have shown that gelatine made with water 

 alone absorbs water at a slower rate from these solutions than from 

 distilled water. Since a number of workers in biology and in colloidal 

 chemistry have drawn conclusions based on the assumption that 

 the presence of a substance within a jelly has the same qualitative 

 effect on its capacity for absorbing water as does the presence of the 

 same substance in an external solution, it seemed advisable to test 

 the matter more fully. 



Stiff gelatine jelUes were made as described above, using the follow- 

 ing solutions instead of distilled water: M/2 and M/4 sodium sulphate; 

 2M, M, and M/2 sodium tartrate; 2M, M, and M/2 sodium citrate; 

 2M and M (approximate) ethyl alcohol; M and M/2 cane sugar; M 

 sodium chloride; M ammonium chloride; M sodium bromide. The 

 original water-content and the evaporational history of all jellies 

 compared was always the same. With the exception of the one made 

 with cane sugar, all of these jellies absorbed distilled water at a faster 

 rate than did jellies made with water alone. This was found to be 

 true also after the jellies had been evaporated to dryness. 



It seemed possible that when the gelatine and salt solutions were 

 heated to 60° C. a chemical change might have taken place which does 

 not occur at the temperatures at which the imbibition experiments 

 were carried on and that here might be an explanation of the difference 

 in behavior when the salts are made up in the jelly and when they 

 act in the surrounding solution. In order to introduce the salts into 

 the jelly without heating them with the gelatine, the gelatine jelly 

 was made with water in the usual way, and after setting it was 

 allowed to absorb all of a small measured quantity of the solution 

 whose presence was desired in the jelly. Then this jelly containing 

 the solution was placed in distilled water. Again it was found that, 

 with the exception of cane sugar, the jellies containing the substances 



* Cainegie Inst. Wash. Year Book for 1917, p. 69. 



