1. US Patent 3,526,172 (1970).
2. Black, Sivalls and Bryson. Inc, Water Poll. Cont. Res. Repts., Envir. Prot. Agency (1971).
3. US Patent 3,607,327 (1971).
4. Meyers, S. L., Rock Products, 96 (1949).
5. Verbeck, G. J., ASTM Special Tech. Publ., 205, 17 (1958).