CHAPTER XVII 



COLLOIDAL SUBSTANCES, COLLOIDAL STATE, AND 

 COLLOIDAL BEHAVIOR 



Graham had suggested the distinction between colloidal and 

 crystalloidal substances, but it was found later that one and the 

 same substance, e.g., NaCl," may behave when in solution either 

 as a crystalloid or as a colloid. It then was proposed to drop the 

 distinction between colloidal and crystalloidal substances and to 

 distinguish between the colloidal and the crystalloidal state of 

 matter. The reasons are summed up in the following quotation 

 from Burton: 



" Modern work has shown that it is incorrect to speak of colloidal 

 substances as a particular class. Krafft has observed that the alkali 

 salts of the higher fatty acids stearate, palmitate, oleate dissolve 

 in alcohol as crystalloids with normal molecular weights, but in water 

 they are true colloids. The reverse is true of sodium chloride; Paal 

 found that the latter gave a colloidal solution in benzol, while, of course, 

 it gives a crystalloidal solution in water (Karczag). More recently, 

 von Weimarn has demonstrated, by the preparation of colloidal solu- 

 tions of over two hundred chemical substances (salts, elements, etc.), 

 that, by proper manipulation, almost any substance which exists in 

 the solid state can be produced in solution, either as a colloid or as a 

 crystalloid; and that, as shown by many other workers, in some cases 

 it is merely a matter of the concentration of the reacting components 

 whether one gets crystalloidal or colloidal solutions. 



''Consequently, we now speak of matter being in the colloidal state 

 rather than of certain substances as colloids the essential character- 

 istic of the colloidal state being that the substance will exist indefinitely 

 as a suspension of solid (or, in some cases, probably liquid) masses of 

 very small size in some liquid media, e.g., water, alcohol, benzol, gly- 

 cerine, etc. According to the medium employed the resulting solutions 

 or suspensions are called, after Graham, hydrosols, alcosols,benzosols, 

 glycersols, etc." 1 



1 BURTON, E. F., The Physical Properties of Colloidal Solutions, 2d ed., 

 pp. 8-9, London, New York, Bombay, Calcutta, and Madras, 1921. 



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