1. R. J. Lishka, Water Metals No. 3. U. S. Department of Health, Education and Welfare, Public Health Service, Cincinnati, Ohio (1965).
2. P. G. Brewer and D. W. Spencer, Trace Element Intercalibration Study Reference No. 70–62, Woods Hole Oceanographic Institution, Woods Hole, Mass. Dec. 1970 (Unpublished Manuscript).
3. H. Gysel, Mikrochim. Acta 1953 266; 1956 577.
4. D. E. Robertson, Anal. Chem. 40 1067 (1968).
5. J. I. Hoffman and G. E. F. Lundell, J. Research National Bureau of Standards 22 465 (1939).