Field tests for the colorimetric determination of the molluscicide Bayer 73.

A simple and accurate field test for the estimation of the active principle in biologically active substances, such as molluscicides, that are used in high dilution is necessary for the proper control of the application of such substances. Colorimetric methods have proved very successful in this connexion, and the present paper describes two such methods for the quantitative determination of 5,2'-dichloro-4'-nitrosalicylicanilide-the active ingredient of the molluscicide Bayer 73-in very low concentrations. In the first method, the molluscicide is extracted from the water sample with amyl acetate, a methanolic solution of sodium hydroxide is added to the extract, and the resulting yellow colour is measured at 385 mmu in an electrophotometer. In the second method, the dye safranin is added to the sample, the colour complex then formed with the molluscicide is extracted with a mixture of organic solvents, and the colour intensity of the extract is determined by means of a wedge colorimeter, which does not need electric current for its operation. The first method, though more exact, is less suitable for use in the field than the second method, which is simpler and gives results of acceptable accuracy.