GENERAL CHEMISTRY OF THE PROTEINS 5 



until formation of a finely divided disperse phase occurs. The 

 theory of the main methods of formation of the colloidal 

 state of all substances and the general formulation of the 

 conditions of their existence has been developed by P. P. von 

 Weimarn. 



Finally, solutions of colloidal character are obtained when 

 substances of very high molecular weight are dissolved in water. 

 The tendency of the large molecules to associate and polymerise 

 can still further increase the colloidal properties of these solu- 

 tions. Albumin, starch, glycogen, etc., are included in this 

 group of substances, whose main characteristic is that they 

 occur exclusively in the colloidal condition. 



Let us suppose that, instead of a dilute solution of a substance 

 of low molecular weight, the same total quantity of material is 

 present as much larger particles, which, in consequence, are 

 fewer in number. Clearly such properties as depend on the 

 number and size of the particles will in consequence be con- 

 siderably altered. The osmotic pressure would fall, to a small 

 value ; the power of penetrating membranes, as also the rate of 

 diffusion in general, would become minute ; while the directive 

 force which orientates particles for formation of crystals 

 becomes very weak or can be no longer developed. Accord- 

 ingly, no qualitative difference between typical dilute solutions, 

 as of sugar or salts, and colloidal solutions is to be expected, but 

 merely a gradual transition from the one to the other. 



In the second place, the characteristics of the latter solutions 

 would appear. First, whereas in a very dilute solution of a 

 substance of low molecular weight, the volume of the solid can, 

 as a rule, be neglected, in a colloidal solution the volume of the 

 particles is appreciable in consequence of their size. Secondly, 

 the particles are often so large as to be visible when refined 

 optical methods are used, e.g., by observing with the naked eye 

 at right angles the fog produced by a bright beam of incident 

 light (Tyndall's phenomenon), or the diffraction images in the 

 microscope (ultramicroscope) . The disperse phase develops 

 physical surfaces in the medium of dispersion, so that the most 

 varied reactions of the two phases can be fixed or modified 

 according to the physical properties of these surfaces. 



