The purity of the compound can be ascertained by dissolving in glacial acetic acid, adding potassium iodide, and titrating with thiosulphate; 0.1 gram should require 14.8 to 14.9 c.cms. of N/10 sodium thiosulphate. Each chlorine atom in halazone is equivalent to 1 molecule of hypochlorous acid and the “available” chlorine content is consequently 52.5 per cent or double the actual chlorine content.
>SO2·NCl2 + 4HI = >SO2·NH2 + 2HCl + 2I2.
From the bacteriological results given by Dakin and Dunham it would appear that 3 parts per million of halazone (1.5 p.p.m. available chlorine) are sufficient to sterilise heavily polluted waters in thirty minutes and that this concentration can be relied upon to remove pathogenic organisms.
The formula recommended for the preparation of tablets is halazone 4 per cent, sodium carbonate, 4 per cent (or dried borax 8 per cent), and sodium chloride (pure) 92 per cent.
Halazone and halazone tablets, when tested in the author’s laboratory on the coloured Ottawa River water seeded with B. coli, have given rather inferior results. With 1 tablet per quart, over six hours were required to reduce a B. coli content of 100 per 10 c.cms. to less than 1 per 10 c.cms. Clear well waters gave excellent results and large numbers of B. coli were reduced to less than 1 per 10 c.cms. in less than thirty minutes. McCrady[B] has also obtained excellent results with various strains of B. coli seeded into the colourless St. Lawrence water.
[B] Private communication.
BIBLIOGRAPHY
[1] Raschig. Chem. Zeit., 1907, 31, 926.
[2] Rideal. S. J. Roy. San. Inst., 1910, 31, 33-45.