Colour in relation to chemical constitution of the organic salts and metallic derivatives of isonitrosodiphenyl-thiohydantoin

1. Isonitroso-1:3-diphenylthio-hydantoin has been obtained for the first time by the action of nitrous acid on 1:3-diphenylthio-hydantoin. 2. Isonitroso-diphenylthio-hydantoin has a bright yellow colour in the solid state or in solution in organic solvents, but on treatment with alkalies or organic bases, intense crimson coloured salts are formed the transition of colour from yellow to crimson being sufficiently strong and sharp for the compound to act as an excellent indicator. 3. The change of colour of the above compound from yellow to crimson has been shown from theoretical considerations to be due to a fundamental change in the constitution of the molecules from an oximinoketonic to a nitroso-enolic form. 4. The above change is quite in accordance with a "Theory of colour on the basis of molecular strain," advanced by Dutt