CYTOPLASM 



[49 



surface of the ion decreases. Fig. 99 shows a graphical representation 

 of the water layers. It demonstrates how the ionic radii grow with 

 increasing atomic weight while the water layers decrease. 



If a gel swollen in water is imbibed with salt solutions, the pene- 

 trating ions will weaken the electric field of the hydrophilic dipole 



TABLE XVI 

 ION RADII 



groups of the gel frame; consequently their hydration decreases, 

 which results in shrinkage. In the case of biogels this effect of shrinkage 

 in neutral salts is observed only in rather concentrated salt solutions 

 (from about N/z upwards) which in most cases must be considered 

 to be non-physiological. Shrinkage by means of salt can therefore be 

 used for preserving purposes (brining of meat) or for the salting-out 

 of dissolved proteins. 



The degree of shrinkage depends on the radius of the hydrated ions 

 as long as other conditions remain constant. For instance, if dried agar 

 powder swells in Normal alkali chloride solutions (Brauner, 1932), 

 the degree of sweUing is less than in water, and it is found that by 

 comparison with the other alkali ions, Li and Na ions result in a higher 

 degree of swelling, in accordance with the series of Fig. 99 : 



Fig. 99. Hydration. Ions of the alkali series; hydration layer dotted. 



