CHAPTER VIII 

 DISPERSE SYSTEMS 



I. COLLOIDS— THE RESERVOIRS OF ENERGY 



" The properties of colloidal solutions can be most efficiently inquired into by 

 application, as far as possible, of the same views and methods as those generally 

 applied to true solutions."" Sorensen. 



Protoplasm consists largely of water. For instance, about 85 per 

 cent, of the total body weight of a puppy is water. This water is 

 partly " free," i.e. may readily be removed Ijy gentle drying, and 

 partly " bound," removable only by destruction of the tissues. 

 The bound water may amount to as much as 1-8 grams for every 

 gram of dry matter in the animal. Obviously, some mechanism 

 must exist to keep this fluid in position and so to mask it as to give 

 the impression of more or less solid tissue. The part of water- 

 holders is played by colloids, emulsions and certain crystalloids. 



In Chap. V. colloids were mentioned as a series of substances 

 which when dissolved in water have a lower osmotic pressure 

 than would be expected from their molecular weight. The reason 

 for this, deduced from the colligative properties of their solutions, 

 is that in water they form aggregates or particles of extra-molecular 

 size. 



The effect of this is enormously to increase the effective surface 

 of the solvent. Therefore the phenomena of surface tension and 

 surface adsorption will be marked. 



The appended table makes clear the enormity of the increase 

 in surface that takes place when a sphere is divided into a large 

 number of small shot and these are, in turn, divided into particles 

 of colloidal size (Table IX.). 



This table shows how a molecular solution of particles of 0-1 /a/x 

 radius acquires an additional effective surface of 12,600 sq. metres 

 when the particles are increased in size sufficiently to bring them 

 into the colloidal realm. A surface is effective when its area is 

 large enough to accommodate the heads (or tails as may be) of 

 molecules which may be held end-on to it. The diameter of the 

 cross-section of most molecules can readily' be calculated, and so 

 the possibility of their adsorption to particles of any particular 

 size may be predicted. In this connection Wo. Ostwald has 



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