[1] Weldon and Powell. Eng. Rec., 1910, =61=, 621. [2] Clark and De Gage, 41st Annual Rpt. Mass. 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 Assoc., 1915, =2=, 679. [8] Young. J. Amer. Public Health Assoc., 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. Potassium bichromate solution. Dissolve 0.025 gram of potassium bichromate 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 quantitative determination compare the colour with that of standards in similar tubes prepared from the solutions of copper sulphate and potassium bichromate. The amounts of solution for various standards are indicated in the following table: PREPARATION OF PERMANENT STANDARDS FOR CONTENT OF CHLORINE --------------------+-------------------+----------------------- Chlorine. | Solution of | Solution of | Copper Sulphate. | Potassium Bichromate. Parts per million. | c.cms. | c.cms. --------------------+-------------------+----------------------- 0.01 | 0.0 | 0.8 .02 | 0.0 | 2.1 .03 | 0.0 | 3.2 .04 | 0.0 | 4.3 .05 | 0.4 | 5.5 .06 | 0.8 | 6.6 .07 | 1.2 | 7.5 .08 | 1.5 | 8.7 .09 | 1.7 | 9.0 .10 | 1.8 | 10.0 .20 | 1.9 | 20.0 .30 | 1.9 | 30.0 .40 | 2.0 | 38.0 .50 | 2.0 | 45.0 --------------------+-------------------+----------------------- [Illustration: DIAGRAM XV] [Illustration: DIAGRAM XVI] NAME INDEX A Adams, 66, 82 B Bassenge, 9 Baxter, 4 Berge, 9 Berthollet, 1 Bevan, 29 Bonjean, 36 Bray, 24 Breteau, 26 Bucholtz, 5