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

Date:
1887
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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.

    742/838 (page 690)
    4. Determination of the Organic Matters and their Products in Water. As already stated, the determination of organic matter in water is difficult, and many processes have been proposed. Some are obviously out of the question for medical officers, save in exceptional circumstances. Those, therefore, are described here which are not only likely to give sufficient information for hygienic purposes, but also to be within the range, for the most part, of the medical officer's apialiances. constitution of the magnesia and soap compound is variable. The result must be considered as quite appro.-timative, but may sometimes be rendered more accurate by diluting with dis- tilled water. Take 200 c.c. of water; add to it the number of drops of solution of ammonium oxalate known to be sufficient by the lime experiment; allow to stand for twenty-four hours; filter, boil for half an hour, replace loss by distilled water ; allow to cool in the vessel, which should be well corked, and determine hardness in 50 c.c. As the lime has been thrown down and the carbonic acid driven off, the hardness is owing to magnesian salts of some kind. Calculate as magnesia, the coefficient of which, for each measure of soap solution, is O'l, or, as magnesium, the coefficient of which is 0 06. Example.—Hardness, after driving off carbonic acid by boiling and precipitating lime = 7 (7-2) X 0-l-(-2=l-0 part of magnesia per 100,000; 1-0 x 0-7=07 grain per gallon. Or multiply the number of measures corrected for lather by 0'2, the result is parts per 100,000: or by 0'14 ; the result is grains per gallon. Although this result is approximative, it is really nearer the truth than the determination by weighing in the hands of a beginner. Free Carbonic Acid by the Soap Test.—In order to get rid of the fallacy from free carbonic acid acting on the soap, Clark recommended that the water should be well shaken in a bottle, so as to disengage some of the COj, and then that the air should be sucked out. But this does not entirely remove the carbonic acid. By the soap test the free carbonic acid can be determined in the following way :—Throw down all the lime carefully by ammonium oxalate, without adding an excess, and determine the hardness in 50 c.c. as usual. The hardness will be owing to magnesian salts and carbonic acid. If now the water, freed from lime, be boiled, and the loss of water replaced by dis- tilled water, the carbonic acid will be driven off. The hardness should be then again determined. The difference between the first and second trials will give the amount of soap solution which had been previously acted on by the carbonic acid. Example.—1. Total magnesian and carbonic-acid hardness, = 12 measures. 2. Magnesian hardness, . . . • — 7 ,, Carbonic-acid hardness, . . . = 5 „ 1 measure of soap sol. corresponds to 0 22 milligrammes carbonic acid. Therefore, 0'22 X 5 X 2=2'2=;centigrammes per litre, or parts, by weight, in 100,000, and 2'2 x 0'7 = 1 54 grains per gallon. But gases are usually stated in volume, either c.c. per litre or cubic inches per g.al]on. Now 1 centigramme = 506 c.c, therefore 2'2x5'06 = 11]32 c.c. per litre; or multijily the 7ict measures of soap by 2 23; 5 x 2'23=11 '15, which is sufficiently near. To bring to cubic inches per gallon multiply the grains by 2, thus : l54x2=3'08 cubic inches, since 2 cubic inches weigh 1 grain at 32° F. and 30 in. barometer, or multiply the net measures of soap by 0-616 ; thus: 5x0'616=3'08 cubic inches. To convert c.c. per litre into cubic inches i^er gallon, divide by 3-61; thus; ir 132-^3-61=3-08. Determination of Lime and Magnesia by Weight. It may be desired to determine the lime and magnesia by weight, and the following pro- cesses can then be used :— Lime by Weight.—Take a known quantity of water ; add ammonium oxalate, and then ammonia enough to give an ammoniacal smell. Allow precipitate thoroughly to subside, and then wash by decantation, or by throwing the precipitate on a small filter of Swedish paper, the weight of the ash of which is known. Decantation is recommended. If a filter is used, wash precipitate on filter ; dry ; scrape precipitate from filter, and place in a plati- num crucible ; bum filter to an ash, by holding it in a strong gas flame, and place it also in the crucible. Heat the crucible to gentle redness for fifteen minutes, moisten with a little water, and test with tui-meric paper. If no reaction is given, the process is done. If the paper is browned (showing presence of caustic lime), reoarbonate with ammonium carbonate, drive off excess of ammonia, dry, and weigh. Tlie substance weighed is calcium carbonate; multiply by 056, and the result is lime ; or by 0 'iO for calcium alone.