Abstract
(1) The foam formation of mixed aqueous solution containing saponin in a constant amount and ethyl alcohol in varying concentration was studied. Life of the foam produced in aqueous solutions of saponin (concentrations being 0.009085 g./l. and 0.001820 g./l.) is remarkably increased in length by the addition of alcohol within the region of concentration covering over from 0.0026 mol/l. to 0.77 mol/l. Addition of alcohol in concentration exceeding 0.77 mol/l. again renders the foam unstable. (2) Attempts were made to explain the mechanism of foam formation relating to the above phenomena. (3) Foam and hydrosol were compared with respect to their properties as a disperse system, from which some resemblances as well as differences were pointed out between them.

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