DEPARTMENT OF BOTANICAL RESEARCH. 



69 



evaporation rate to half that of neutral gelatine. However, it devel- 

 oped that sodium sulphate, sodium acetate, and sodium tartrate, salts 

 which are given in the Hofmeister series as decreasing the adsorption, 

 also decreased the evaporation rate. But when parallel tests of absorp- 

 tion were made it appeared that when these salts were made up in 

 the gelatine and the gelatine placed in distilled water, they too increase 

 the absorbing capacity of the gelatine. The accompanying tables give 

 samples of the results obtained. Corrections were made for loss or gain 

 due to exchanges between the gelatine and the surrounding liquids. 



Average gain in weight per hour per gram of gelatine for first 3 hours. 



Average gain in weight per hour per gram of dry gelatine for first 3 hours. 



The work was scarcely begun before it became evident that the ab- 

 sorption rate of gelatine is greatly influenced by its history from the time 

 of "setting" to the beginning of the tests. Before comparable results 

 could be obtained the influence of this history had to be investigated. 



As was to be expected, the water-content of the gelatine at the 

 beginning of the absorption strongly influences the rate of water intake, 

 so that great care must be taken to have ail the gelatine of the same 

 water-content at the start. Even when the gelatine used has the 

 same water-content at the beginning of the experiment, its ability to 

 absorb water still depends upon its water-content when it was made up, 

 as the table on page 70 shows. Several lots of gelatine were made up 

 to the concentrations indicated in the table and all lots allowed to 

 evaporate water at room temperature until tests showed that they 

 had attained the same water-content. Then pieces of the same size 



