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Abstract Molybdenum forms a green precipitate with dithiol (4‐methyl‐1: 2‐dimercaptobenzene) in acid solutions and this precipitate is soluble in amyl acetate, giving an intensely coloured solution. This reaction is the basis for an extractive method for the determination of small amounts of molybdenum, of the order of 0.2 to 25 μg., occurring in plant materials. The sample is digested with nitric, sulphuric and perchloric acids, and copper extracted with dithizone and determined as usual, if so desired. The digest is then acidified and molybdenum, along with certain other metals, extracted by means of cupferron and chloroform. After the destruction of cupferron the molybdenum‐dithiol complex is precipitated, extracted into amyl acetate and its absorption determined in a photoelectric colorimeter. The method is accurate and extremely sensitive. Since it enables the determination of both copper and molybdenum in the same digest, it represents an economy of time and reagents when both determinations are required.
Piper et al. (Fri,) studied this question.