The application of thiosalts in analysis : A new scheme of qualitative analysis - part a

Abstract

1. A new scheme of qualitative analysis for mixtures containing the common as well as the so-called “rare” elements has been discussed. 2. The new scheme is based upon the immediate formation of thiosalts by metals of the arsenic group (and vanadium) on adding concentrated ammonium sulphide solution and the subsequent decomposition of the thiosalts with excess of hydrochloric acid. 3. This scheme has the following advantages over the classical scheme now in use: a. The slow precipitation of the copper and arsenic groups by hydrogen sulphide in hydrochloric acid solution has been replaced by a more simple and rapid method of precipitating the sulphides completely. A considerable saving of time taken in analysis is thus effected. b. The use of the hydrogen sulphide gas which is extremely inconvenient especially in large classes of students, has been eliminated and its place has been taken by concentrated ammonium sulphide—a reagent which can be easily prepared and used as a shelf reagent. c. The use of yellow ammonium sulphide which does not give a satisfactory separation of the copper group from the arsenic group has been eliminated. d. As the main features of the new scheme are similar to those of the classical scheme the student who has been trained in the old technique can take to the new scheme without much difficulty.