The Handbook of Soap Manufacture

Detergent Action of Soap.--The property possessed by soap of removing dirt is one which it is difficult to satisfactorily explain. Many theories, more or less complicated, have been suggested, but even now the question cannot be regarded as solved.

The explanation commonly accepted is that the alkali liberated by hydrolysis attacks any greasy matter on the surface to be cleansed, and, as the fat is dissolved, the particles of dirt are loosened and easily washed off. Berzelius held this view, and considered that the value of a soap depended upon the ease with which it yielded free alkali on solution in water.

This theory is considered by Hillyer (Journ. Amer. Chem. Soc., 1903, 524), however, to be quite illogical, for, as he points out, the liberated alkali would be far more likely to recombine with the acid or acid salt from which it has been separated, than to saponify a neutral glyceride, while, further, unsaponifiable greasy