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Chlorination is an invaluable adjunct to other forms of water purification and it is not improbable that, in the future, filter plants will be designed to remove aesthetic objections at the lowest possible cost and that chlorination will be relied upon for bacterial reduction.
Chlorination is the simplest, most economical, and efficient process by which the removal of bacteria can be accomplished and there is no valid reason why it should not be used for that purpose.
The popularity of this process has suffered through the efforts of over zealous enthusiasts who have been unable either to recognize its limitations or to appreciate the fact that a domestic water supply should be something more than a palatable liquid that does not contain pathogenic organisms. Every system of water purification has its limited sphere of utility and chlorination is no exception to the rule.
BIBLIOGRAPHY
[1] Weldon and Powell. Eng. Rec., 1910, =61=, 621.
[2] Clark and De Gage, 41st Annual Rpt. Ma.s.s. State B. of H. 1910.
[3] Houston. 12th Research Rpt. Metropolitan Water Board, London.
[4] Ellms. Eng. Rec., 1911, =63=, 388.
[5] Johnson. Eng. Rec., 1911, =64=, No. 16.
[6] Jennings. 8th Inter. Congr. Appl. Chem., =26=, 215.
[7] Longley. J. Amer. Waterworks a.s.soc., 1915, =2=, 679.
[8] Young. J. Amer. Public Health a.s.soc., 1914, =4=, 310.
APPENDIX
ESTIMATION OF CHLORINE IN CHLORINATED WATERS
REAGENTS. 1. Tolidine solution. One gram of _o_-tolidine, purified by recrystallization from alcohol, is dissolved in 1 litre of 10 per cent hydrochloric acid.
2. Copper sulphate solution. Dissolve 1.5 grams of copper sulphate and 1 c.cm. of concentrated sulphuric acid in distilled water and dilute the solution to 100 c.cms.
3. Pota.s.sium b.i.+.c.hromate solution. Dissolve 0.025 gram of pota.s.sium b.i.+.c.hromate and 0.1 c.cm. of concentrated sulphuric acid in distilled water and dilute the solution to 100 c.cms.
PROCEDURE. Mix 1 c.cm. of the tolidine reagent with 100 c.cms. of the sample in a Nessler tube and allow the solution to stand at least five minutes. Small amounts of free chlorine give a yellow and larger amounts an orange colour.
For quant.i.tative determination compare the colour with that of standards in similar tubes prepared from the solutions of copper sulphate and pota.s.sium b.i.+.c.hromate. The amounts of solution for various standards are indicated in the following table:
