The assay of Rochelle salt
MacLeod, Malcolm Joun
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The author has reported in a previous paper, the results of an investigation of the United States Pharmacopoeia XI method for the assay of Rochelle salt. In this investigation, it was found that all samples of Rochelle salt bought on the market, were below standard requirement by the official method, were below standard requirement when assayed by the official method. The United States Pharmacopocia XI requires that Rochelle salt contain no less that 99 percent of KNaC4H6O6.4H2O. The results obtained indicated that the samples assayed were close to 90 percent. To account for this discrepancy the following possibilites were considered as probable explanations; (1) the official method gives erroneous results, (2) the samples were not of standard quality, and (3) the requirements were too high. Since the samples assayed were from large chemical companies, and all of them gave the same result, it was assumed that these samples were very likely representative of the Rochelle salt available, and would be of standard quality. References were fiven to the literature where it is reported that it is difficult to obtain pure crystals of potassium and sodium tartrate. When the salt is crystallized by the usual method, it was found the product obtained was a mixture of potassium and sodium tartrate, potassium tartrate and sodium tartrate.
Thesis (M.A.)--Boston University, 1940