Formation of Periodic Precipitates in the Absence of a Foreign Gel

Abstract

RECENTLY many workers¹ have reported on the formation of periodic precipitates in the absence of another gel. We have obtained periodic precipitates in the slow coagulation of sols of ferric hydroxide, chromic hydroxide, and stannic hydroxide by small quantities of univalent electrolytes like potassium chloride and sodium bromate. Freshly precipitated ferric hydroxide was peptised by the minimum quantity of acetic acid, which was then boiled off ; the sol was further purified by hot dialysis. The concentration of the purified sol was 39.2 gm. per litre. The chromic hydroxide sol was obtained by adding ammonium carbonate solution to hot chromic chloride and then purified by continuous hot dialysis. The concentration of the purified sol was 32.5 gm. per litre.