A manual of practical hygiene / by Edmund A. Parkes ; edited by F.S.B. Francois de Chaumont.

Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene / by Edmund A. Parkes ; edited by F.S.B. Francois de Chaumont. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    127/820 (page 85)
    any faulty action in the filtering beds of the municipal water-works was at once detected. 5. Oxidisable Matter in Water. The oxidisable matter in water consists of oxidisable organic matter, nitrites, ferrous salts, and sulphuretted hydrogen. The last can be easily recognised by the smell, and got rid of by gently warming the water. Ferrous salts are rare,_but, if present, they impart a distinct chalybeate taste to the water if their amount reaches the fifth of a grain of iron per gallon (about 3 milligrammes per litre). Generally their presence may be disregarded. There remain, therefore, the oxidisable organic matter, and nitrous acid as nitrites. For determining these the potassium permanganate is very con- venient. (a) Total Oxidisable Matter in terms of Oxygen required for its Oxidation.— A solution of potassium permanganate is made by dissolving 0-395 grammes of the crystallised salt in one litre of water. In presence of an acid each C.C. of this solution is capable of yielding 0-1 milligramme of oxygen. To test its accuracy a standard solution of oxalic acid is made by dissolving 0-7875 grammes of crystallised oxalic acid in one litre of water : 100 C.C. acidulated with dilute sulphuric acid, and warmed, should exactly decolorise 100 C.C. of permanganate solution. Process.*—Take a convenient quantity of the water to be examined, say 250 C.C.; add 5 C.C, of dilute sulphuric acid (1 to 10); drop in the permanganate solution from a burette until a pink colour is established ; warm the water up to 140° Fahr. (60° C), dropping in more permanganate if the colour disappears; when the temperature reaches 140° Fahr. remove the lamp ; continue to drop in permanganate until the colour is permanent for about ten minutes. Then read off the number of C.C. used, multiply by 0-1 to get the milligrammes of oxygen, and by 4 to get the amount per litre. Exc^t~2^ GG of water> with 5 C.C. of dilute sulphuric acid, re- quired 6 -5 C. C. of permanganate to give a permanent colour ;3-5x0-1x4 = 1-4 milligrammes of oxygen per litre required for total oxidisable matter, f It must be remembered that this includes both organic matter and nitrous acid. We must now differentiate these. ti2] %Z%nXrnaMfe M?ltt? ™ terms °f Oxygen required for its Oxida- l?he examined; add 5 C.C. of dilute sulphuric down to U0°;A ^n\e\inSklj f°P 20 then allow it to cool ,W, r 1 i f !' ( G) J fcten aM the Pennanganate until a pink colour s established for ten minutes. Calculate out the oxygen as above statm he result as nulhgramines per litre required for oxidisable organic matte for shortly, as organic oxygen. ° ui, withsuTSVid^r0688 iS.the ^rMnS off of the nitl™s acid ^ WBng position! 18 aScertamed that ^ can be done without decom- thi dirTrenrP W™^? T n°W he detennined easily by calculating from «^Z^teT?7?e PreC6ding PTOCeSSeS- Each milligramme of