1. Association of Official Agricultural Chemists (1960). Official Methods of Analysis, edited by W. Horwitz, 9th ed. Washington D.C.
2. Borick, P. M., Dondershine, F. H., and Chandler, V. L. (1964). J. pharm. Sci., 53, 1283.
3. Kelsey, J. C., Beeby, M. M. and Whitehouse, C. W. (1965). Mth. Bull. Minist. Hlth Lab. Serv., 24, 152.
4. Pepper, R. E., and Chandler, V. L. (1963). J. appl. Micro. biol., 11, 385.
5. Rideal, S., and Walker, J. T. A. (1903). J. roy. sanit. Inst., 24, 424.