COLLOIDS IN PROTOPLASM 



colloids may be called Suspension Colloids. From 

 coarse suspensions to suspension colloids there 

 exist all kinds of intermediate suspensions. The 

 platinum sol and the other metal sols mentioned 

 above belong, according to their action and to their 

 physical properties, to the suspension colloids. 

 They have been of great use in studies on suspen- 

 sion colloids. Quantitative analysis showed that 

 even in suspension colloids the amount of the 

 solid phase is very small in comparison with the 

 quantity of the liquid medium Suspension colloids 

 have very few points of resemblance with solutions. 

 They do not conduct electric currents but to a 

 slight extent, and they do not show alteration 

 from the freezing-point of their liquid medium. 

 Cataphoresis has been quite generally noticed 

 even in suspension colloids. In fact, suspension 

 colloids are nothing else but cases of ultramicro- 

 scopic suspension. The only one important differ- 

 ence from coarse suspensions is the great stability 

 of suspension colloids. Platinum sol or the colloid 

 solution of hydroxide of iron or any other suspen- 

 sion colloid may be kept for years without showing 

 any alteration. Since the suspended particles are 

 considerably smaller, we must believe that the 

 surface of contact between the suspended substance 

 and the medium (we speak nowadays of the 

 Medium of Dispersion] is much larger in suspension 

 colloids than in coarse suspensions. We may con- 

 sider this to be the reason for the greater stability 

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