Water analysis for sanitary purposes, with hints for the interpretation of results / by E Frankland.
- Date:
- 1890
Licence: Public Domain Mark
Credit: Water analysis for sanitary purposes, with hints for the interpretation of results / by E Frankland. 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.
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![DETERMINATION OF HAKDNESS, 2] Towards the close of the operation, the yellow liquid is rendered so opalescent by the precipitated argentic chloride, that it is somewhat difficult to detect exactly the completion of the reaction. In cases requiring great accuracy, therefore, it is advisable, after the amount of chlorides has been roughly determined in one flask, to pour iuto it a little of the water or of a solution of any chloride, so as to destroy the red tint, and to permit the flask to remain beside the one in which a second volume of 50 c.c. of the water is being tested. By comparing the tint of the liquid in the second flask with that in the first (known to be underdone), the first tinge of red is easily distinguished. Before throwing away the contents of the second flask, the experimenter may make sure that the reaction was really finished by adding another drop of the silver solution, when a much more marked red tint will be produced if all the chlorine has already been precipitated. Hardness. The method of procedure for this estimation is simple, and there will be no difficulty in obtaining concordant and accurate results if the following directions are adhered to; but uniformity of working is essential. Take a bottle of say 8 ounces capacity, with an accurately fitting stopper, pour in 50 c.c. of the water, agitate thoroughly, and then suck out the air from the bottle through a glass tube, so that any carbonic anhydride given off by the water may be thereby removed. Next add 1 c.c. of a standard solu- tion of soap (instructions for making this are given in Appendix I, E), shake the bottle vigorously, and repeat the process after each addition, decreasing the quantity of soap test added from time to time untd, as the reaction is ap- proaching completion, the soap solution must be added drop by drop. When a good froth has been obtained by shaking, the bottle is laid down on its side; and, if the lather remains permanent for the space of Ave minutes, the operation is](https://iiif.wellcomecollection.org/image/b21995916_0033.jp2/full/800%2C/0/default.jpg)
