Abstract
COLLOID chemistry, in its widest sense, deals with chemical processes which occur in the immediate neighbourhood of surfaces—that is, chemical effects which are brought about as a result of capillary and electrocapillary forces. Such effects are necessarily limited to a small range, the thickness of the capillary layer being of the order 10-6 to 10-7 cm. It is obvious that these effects can become of importance only if the surface area itself is very large. Under ordinary conditions, in which two fluid masses in bulk are separated by a definite surface—as in distribution phenomena—the capillary effects are too small to be observed. To magnify the effect it is usually necessary to realise a state of affairs in which one phase is distributed in a state of fine subdivision or “dispersed” through the other phase or medium. In these circumstances the total inter-facial area is enormously great. We find such conditions in the case of fine suspensions (diameter of particle 10-4 cm. approx.), emulsions (diameter of particle 10-5 cm.), and colloid solutions (diameter of particle 10-6 cm. approx.). Colloidal solutions are systems in which the solute individuals or sols, though apparently soluble, have not broken down to the molecular limit, but consist instead of aggregates, composed roughly of several hundred molecules or atoms. Such soluble aggregates or sols will not diffuse through membranes (as Graham showed in his original work on the colloidal state), and thus differ markedly from the behaviour of dissolved crystalloids, e.g. salts.
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LEWIS, W. Colloids and Chemical Industry 1 . Nature 101, 66–67 (1918). https://doi.org/10.1038/101066a0
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DOI: https://doi.org/10.1038/101066a0