Sols and Gels — Relation to Protoplasmic Structure 



87 



ions is not influenced by the structure of thixotropic sols and gels, 

 which is very coarse compared to the small size of the ions. 



Finally, not only gels but also sols of this type (gelatin, soaps, 

 etc.) show elastic properties. Small solid particles suspended in 

 such a sol may be moved by an external force but return to their 



Fig. 1. 



original position when the force stops acting, a phenomenon not ob- 

 served in Newtonian liquids.'' This elasticity in sols is not found so 

 regularly as the other characteristic properties just mentioned. The 

 presence of distinctly rod-shaped colloidal particles is perhaps more 

 decisive in causing elastic effects than it is with the other properties 

 characteristic of this kind of anomalous viscosity. 



Thixotropic behavior is not exceptional; it is very common, pro- 

 vided that suitable concentrations of the colloid are chosen. Ex- 

 amples are: thixotropic, aqueous gels of many oxides' (aluminum, 

 iron, scandium, vanadium, titanium, thorium, etc.), of colloidal 



