The work of Dr. Jacques Loeb, first at the University of Chicago and later at the Rockefeller Institute for Medical Research, has been a constant stimulus to advanced workers in physical and biologic chemistry. Particularly absorbing has been that phase dealing with colloidal chemistry. This volume epitomizes his work on the subject, and includes much heretofore unpublished material; it is written, however, from the point of view of one presenting his case rather than as a textbook. As Loeb points out, colloid chemistry has been developed on the assumption that the ultimate unit in colloidal solutions is not the isolated molecule or ion, but an aggregate of molecules or ions. As it seemed improbable that such aggregates react with acids, alkalis or salt in stoichiometric proportions, the theory advanced, and generally accepted today, was that eletrolytes are adsorbed on the surfaces of colloidal particles according to a purely empiric formula.