292 PHYSICAL PROPERTIES 



2. The Swelling of Protein Jellies. — A phenomenon which is 

 doubtless very closely allied to that of the solution of solid pro- 

 teins is the swelling or taking up of water which protein jellies 

 undergo when immersed in water or in certain watery solutions. 



When a plate of water-poor gelatin is immersed in water, 

 especially if the water contains a little added acid or alkali, the 

 plate takes up a very considerable quantity of water, many 

 times its own weight, and at the same time swells to relatively 

 enormous dimensions. 



It was first pointed out by Quincke (80) that the swelling of 

 gelatin is accompanied by a volume contraction, that is, the 

 volume of the swollen jelly is less than the sum of the volumes 

 of the original unswollen jelly and the absorbed water, and it 

 was further pointed out by Wiedemann and Ludeking (107) 

 that this process is accompanied by a disengagement of heat. 

 Careful measurements of the heat liberated and the volume 

 contraction during the swelling of casein in water have been 

 made by Katz (46) who finds that the relationship between the 

 heat liberated (= W) and the amount of water {= i grams) 

 taken up by one gram of protein is expressed by the equation : 



in which A and B are constants. This implies that at the initial 

 moment of the swelling process, the heat liberated by one gram 

 of protein per gram of water absorbed will be equal to the ratio 



75, which in this case equalled 265 Cal. The volume-contraction 



follows an analogous relationship : 



fi 



C = 



g + i 



in which / and g are constants and we may similarly calculate, 



f 

 from the ratio - the value of Co, or the volume contraction per 

 9 



gram of protein per gram of water absorbed at the moment of 

 initiation of the process, and this calculation yields the value 

 0.3 cc. 



The time-relations and equilibria in the process of the swelling 

 of gelatin have been especially studied by Hofmeister (40), Pauli 



