29% THE COLLOIDAL STATE 



swelling were made by the botanist, Reinke,* on Laminaria 

 contained in an apparatus known as the Oedometer. 



Only by the application of an opposing pressure of 41 

 atmospheres was he able to reduce the amount of water im- 

 bibed to one-twentieth of the amount it would normally have 

 taken up. 



Conditions Affecting Imbibition. (a) Temperature. Heat 

 is evolved during swelling, as may be seen from the following 

 table taken from Taylor's " Chemistry of Colloids " : 



Cals per gram of Colloid. 

 Gelatine . . . . . 57 



Starch 6'6 



Gum arabic .... 9*0 

 Gum tragacanth . .10*3 



This being so, heat hinders imbibition, while cold and 

 pressure favour it. For this reason it is best in making a 

 solution of a* colloid such as agar or gelatine to allow it to 

 swell for some time in cold water without applying any heat. 



(b) Presence of Impurities. The swelling of colloids is very 

 considerably increased by the presence of small quantities of 

 either acids or alkalies. In the case of fibrin M. H. Fischer f 

 was able to increase the normal swelling in water sixfold by 

 the presence of 0*02 N hydrochloric acid. As a practical ap- 

 plication of this may be mentioned the beneficial effect of the 

 addition of a small quantity of acetic acid to the water em- 

 ployed for swelling agar previous to making a solution. 



With regard to the action of salts, it is found that anions 

 act in the order of the Lyophilic series mentioned on p. 295. 



Thus the following anions favour imbibition : 



CNS > i > Br > NO 3 > C1O 2 > Cl ; 

 while the following inhibit : 



- SO 4 > tartrate > citrate > acetate, 



as do also alcohol, glucose, and cane sugar. 



According to SpekJ salts such as lithium bromide or 



* Reinke: " Hanstein's hot. Abhandl.," 1879, 4, i. 



t This author considers that much of the pathological swelling in animals 

 and man is due to an accumulation of acid in the tissues, which, as a con- 

 sequence,, tend to draw fluid from surrounding tissues and so swell; he would 

 even offer the same explanation for the swelling caused by an insect's bite. 



jSpek: "Koll. Chem. Beihefte.," 1920, 12, i. 



