PHASE RULE OF PYRAMIDON-BARBITAL SYSTEM

The phase rule data of pyramidon (aminopyrine)(P)-barbital (veronal) (B) system were measured by a modified thawing-and-melting method(Auftau-Schmelz- methode).The system is an incongruent one having a eutectic point and a peritectic point.The incongruently melting substance is Pfeiffer's compound (PB),as H. Rheinboldt et al13 explained.Each curve segment,which is smooth in the form, of the liquidus as well as the solidus,excepting the eutectic and peritectic lines, can best be expressed empirically in a functional relation,in which the molecular percentage (x%) of a binary mixture is taken as either a linear function or a quadratic function of temperature expressed in degrees centigrade (t℃).Observed data as to those parts of solidus in which the thawing point varies with the composition are probably new to the system.The method of least squares was generally adopted in those calculations.The coordinate values (x,t) of the eutectic point E and the peri- tectic point C are (19.01,91.47) and (32.31,111.25) instead of the data calculated by the present anther from Rheinboldt's results:(17.43,92.9)and(32.23,109.6)respec- tively.It is highly probable that Rheinboldt's samples in which the values of x lie between 33.4 and 34.0 really showed metastable melting points,as indicated by the mathematical analysis of the liquidus curve.Our results of physico-chemical analysis (Kurnakov) prove that both Veramon (Schering-Kahlbaum A.-G.,Berlin)and Sedalon (Sankyo Pharmaceutical Co.,Tokyo) are approximately equimolecular mix- tures of Pfeiffer's compound (PB) and pyramidon (P),while the new Veramon (Schering Co.,London) nearly consists of one molecule of Pfeiffer's compound (PB) and two molecules of pyramidon (P).Ambiguous conclusions appearing in the recent scientific literature,assuming that P₂B is a eutectic mixture or that Veramon is no- thing but the Pfeiffer's compound etc.,were discussed in the light of the present experimental results.We are,however,unable to explain numerical discrepancy between completely melting points over the peritectic point measured by the present author and those of Rheinboldt et al.Non-additive pharmacological effect as a result of physico-chemical change in pharmaceutical preparations is of pharmaco-chemical importance.