1. Deutschman, A.J., Jr., and I.S. Klaus, Anal. Chem. 32: 1809 (1960).
2. Official Methods of Analysis, 12th edn., Assoc. Off. Anal. Chem., Washington, DC, 1975, Method 3.107.
3. Ibid., Tentative Method Cd 8-5.
4. Smouse, T.H., B.D. Mookherjee and S.S. Chang, Chem. Ind. July: 1301 (1965).
5. Halphen, G., Analyst 22:326 (1897).