Field method for the determination of zinc in soils

A method is described for the field estimation of total zinc in soils. A small sample of soil is fused with potassium bisulfate, the fused mass dissolved in water, buffered at pH 4 to 5.5 with acetate buffer, and sodium thiosulfate added to form complex ions with metals that might cause interference. Measured increments of the sample solution are added to a carbon-tetrachloride-dithizone solution, with vigorous shaking after each addition, until a standard color is obtained in the organic phase. Under favorable conditions up to 60 determinations per day can be made by one man. Comparisons of data obtained by the field method with accurate laboratory analyses of the same samples indicate that the method is sufficiently reliable for reconnaissance surveys.