Some of the characters of coagulated and mechanically-filtered water / by Sheridan Delépine.

  • Delépine, Sheridan, 1855-1921.
Date:
1914
Catalogue details

Licence: In copyright

Credit: Some of the characters of coagulated and mechanically-filtered water / by Sheridan Delépine. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

    18/52 (page 16)
    exceptional and accidental circumstances. The amount of oxygen absorbed by permanganate of potash indicates the amount of oxidisable matter which is chiefly organic matter. The removal of this oxidisable matter is of import- ance, and this was very thoroughly effected by the filters. Condition 11.—The permanent hardness of the water to he increased not less than 10 per cent, above that of the raw water. When dealing with hard water it might be convenient to indicate in percentage terms how much the hardness should be reduced, but in the case of a soft water, when the increase of the hardness has for object the removal of the action which the water has on lead, it is useless to demand a percentage increase. What is wanted is that the water should not act on lead and this can be tested directly. It is also obvious that, when a water is exceedingly soft, a 10 per cent, increase may be quite insufficient to render the water inactive as regards lead. This is actually what happened in one instance. The hardness had been increased by treatment to the extent of 30 per cent, and yet the water had still a marked action on lead. The reaction of the water is a better indicator of its probable action on dead, but even the reaction cannot always be depended upon, and it appears to the author safer to rely on a direct estimation of the actual action of water upon pure lead than to trust to the indications given by hardness or reaction. The reaction is, however, a valuable indicator in the practical working of filters. When one knows the average composition of the water to be tested and the extent of its action on lead, the reaction may be generally used with advantage for the purpose of determining the quantity of chemicals to be used. 1 he tests for reaction given in the second set of conditions quoted at the beginning of this paper, do not, however, seem to the author so suitable in current work as the com-