Hygiene and public health / by B. Arthur Whitelegge.

  • Arthur Whitelegge
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Hygiene and public health / by B. Arthur Whitelegge. Source: Wellcome Collection.

    89/610 (page 77)
    Tests.—I. Qualitative.—A solution of baric chlor- ide with a few drops of hydrochloric acid will give a white precipitate with 40 parts (per million) of sul- phates, but none with 20 parts until after standing. IT. Quantitative.—200 c.c. of sample water are boiled, treated with slight excess of baric cliloride solution and a little hydrochloric acid, and then boiled again and filtered. The precipitate collected on the filter is washed, ignited, and weighed as barytic sulphate, BaSO^. Given the weight of BaSO^ from 200 c.c, the corresponding proportion of HgSO^ per litre will be readily calculated. Carbonates. — Soluble calcic bicarbonate, CaH3(CO.^)2, is found in almost all well and spring- waters. It occurs in excess in chalk, limestone, and dolomite water, but it is wanting in rain and peaty water. . It is precipitated by boiling, in the form of normal calcic carbonate, CaCO.^. Magnesic bicarbon- ate, MgH2(C03)2, found in dolomite water, behaves similarly, but partially redissolves on cooling. Sodic carbonate is occasionally found in natural waters, and may give them an alkaline reaction. Free carbonic acid exists in all waters, and if in excess renders them sparkling and palatable. Apart from this, the importance of the carbonates in water depends entirely upon the bases they contain. Tests.—It is scarcely necessary to enumerate here the ordinary chemical tests for carbonates, since they are not required for hygienic purposes. The deter- mination of temporary hardness will show the amount of calcic and magnesic carbonates. Silicates of soda or alumina are occasionally found in water. Tests.—Half a litre of sample water is evaporated to dryness ; the residue is acted upon by strong hydro- chloric acid, and washed with boiling distilled water ; then it is once more dried, ignited, treated ^^ ith acid,