1. T. Clark, British Patent (1841).
2. (a) J. Porter, British Patent (1876).
3. Dry feed of ground quicklime without a slaker;Hirsch;J. Am. Water Works Assoc.,1962
4. Cold lime soda softening;Applebaum;Ind. Eng. Chem.,1940
5. Cochrane Hot Process Softeners, Bull. 2.01, 1963.