A colorimetric method for the determination of molybdenum in soils

The dithiol (4‐methyl‐1 : 2‐dimercaptobenzene) reagent is more sensitive for the determination of molybdenum than is the more commonly used thiocyanate. A method is described for the determination of molybdenum in soils, in which dithiol is used for the final colorimetric estimation. The soil extract is evaporated to dryness, dissolved in hydrochloric acid and copper extracted with dithizone. Molybdenum is then separated from iron by extraction as the thiocyanate, which is then decomposed by digestion with sulphuric acid. The molybdenum is finally precipitated as the dithiol complex and extracted by amyl acetate for colorimetric estimation. The whole determination can be carried out in a Quickfit test‐tube and is both rapid and accurate. The results indicate that none of the elements commonly found in soils, tested in the quantities in which they normally occur, is likely to interfere with the determination.