Horwitz, W., Fisher, H. J., Robertson, A. H., Epps, J. E. A., & Quackenbush, F. W. (1960). Official methods of analysis of the association of official agricultural chemists (9. ed.). Washington, D.C.: Association of Official Agricultural Chemists.

Horwitz, William, H. J. Fisher, A. H. Robertson, Jr. E. A. Epps, and F. W. Quackenbush. Official Methods of Analysis of the Association of Official Agricultural Chemists. 9. ed. Washington, D.C.: Association of Official Agricultural Chemists, 1960.

Horwitz, William, et al. Official Methods of Analysis of the Association of Official Agricultural Chemists. 9. ed. Washington, D.C.: Association of Official Agricultural Chemists, 1960.