The chemical examination of water, sewage, foods, and other substances : by J. E. Purvis and T. R. Hodgson.

  • Purvis, John Edward.
Date:
1914
Catalogue details

Licence: In copyright

Credit: The chemical examination of water, sewage, foods, and other substances : by J. E. Purvis and T. R. Hodgson. 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.

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    hydrogen, a dark colour will be produced of ferrous sulphide. Place in another Nessler glass a measured quantity of the stand- ard iron solution and repeat the process in the same way, and match the colours as before. The amount of iron can then be calculated. Mineral analysis. Determination of alkalinity. Measure out 500 c.c, of the water into a large flask ; add a few drops of methyl orange as an indicator ; and run in from a burette N/io hydrochloric acid until the yellow colour of the methyl orange just turns to pink; the number of c.c. of N/io acid used multiplied by 0-005 gives the alkalinity in terms of calcium carbonate. Estimation of silica. One litre of the water is placed in a large porcelain dish with about 5 c.c. of concentrated hydro- chloric acid ; the whole is evaporated to small bulk on a water bath ; the contents of the dish are then washed out into a platinum dish and evaporated to dryness ; the residue is dried in the air oven. The dry residue is moistened with a few drops of concentrated hydrochloric acid ; the acid is then evaporated on the water bath and the residue placed in an air oven at 150° C. for 30 minutes. After being in the air oven for 30 minutes, the residue is treated with water, filtered, and the filter well washed with hot water and dried in a water oven. The dried filter paper and residue are placed in a platinum dish and ignited over a Bunsen flame; as soon as a white or nearly white ash is obtained, the dish is placed in a desiccator, allowed to cool and weighed ; the increase in weight of the dish less the weight of the filter paper ash represents silica. Estimation of iron. To the filtrate from the silica deter- mination, add a few drops of bromine and a small quantity of solid ammonium chloride, make alkahne with ammonia, boil and filter, well wash the filter with hot water, dry the filter paper with the iron oxide precipitate in the water oven, and when dry ignite it in a platinum dish and weigh the residue. The weight of the residue less the weight of the filter paper ash represents iron as FcaO;,. Estimation of lime. If the filtrate from the iron determin- ation is large, it must first be concentrated to about 250 c.c. ;