CHEMICAL PHENOMENA IN LIFE 



of the former. Of great chemical and biological 

 interest is the effect of small amounts of salts, i.e. 

 electrolytes, on suspension colloids. If we prepare 

 a colloidal suspension of mastic resin in water by 

 mixing one drop of alcoholic mastic solution 

 with a large quantity of water, and add to the 

 milky liquid a trace of mineral salt solution, after 

 a couple of seconds white flakes of deposit appear 

 in the colourless liquid, and the whole resin 

 colloid is precipitated in flakes. We do not doubt, 

 and our opinion is confirmed by the noteworthy 

 experimental work of Hardy, Bredig, and others, 

 that the electric properties of the colloid play the 

 chief part in this flaking-phenomenon. We have to 

 think that the colloid particles are aggregated or 

 agglutinised by electric influence, and form a 

 deposit when they have reached a certain stage of 

 aggregation. Probably the particles charged with 

 positive or negative electricity attract ions of the 

 contrary charge. Since ions have a much stronger 

 electric charge than colloid particles, one ion may 

 attract a number of colloid particles. By this process 

 there must be formed large masses of the colloid, 

 which are no longer able to remain suspended in 

 the liquid, and form flakes which slowly deposit. 



All colloid solutions or sols which do not show 

 any separate particles either by means of the 

 ordinary microscope or by the ultramicroscope, 

 are at present united under the name of Emulsion 

 Colloids. There is no doubt that just such colloids 



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