1. Stahl, E., Angew. Chem., 73, 646 (1961).
2. Wollenweber, P., J. Chromat., 181, 303 (1961).
3. Separation and Identification of Food Colours Permitted by the Colouring Matter in Food Regulations, 1957 (Association of Public Analysts, 1960).
4. Data Sheets on Food Colours. (W.H.O., 1957).