On the formation of a heat-reversible gel

Abstract

In the course of his study of the cyclic ketonic compounds, Dr. Ruhemann has discovered a substance which is, I think, destined to play an important part in the development of the theory of gelation. The substance is 5 dimethylaminoanilo-3:4 diphenylcyclopentene-1:2 dione,* the formula, being C 6 H 5 C―C:NC 6 H 4 N(CH 3 ) 2 ‖ | C 6 H 5 C CO ⁄ CO It is a solid at ordinary temperature, and occurs either as orange-coloured needles or as small dark red plates; the former separate from dilute solutions, the latter from concentrated solutions in absolute alcohol. “If a little water is added to the hot alcoholic solution, no crystals separate on cooling, but the whole sets to a transparent jelly, which, according to concentration, is yellow or yellowish-red. This gel, when kept at the ordinary temperature, gradually liquefies, and in the course of one or two days completely disappears, with separation from the resulting solution of the azomethine in orange needles.” Dr. Ruhemann has therefore furnished us with a substance which offers special facilities for studying the relations between the crystalline and the colloidal state.