Water analysis for sanitary purposes : with hints for the interpretation of results / by E. Frankland.

  • Edward Frankland
Date:
1890
Catalogue details

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 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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    TKMPORARY HARDNESS. 28 ari-lioiir after a lather has been obtained. If it will no longer lather at the end of this time more soap solution must be added, and this process repeated until a permanent lather is obtained. The soap-destroying measnre thus obtained is called the “ total hardness”; but many waters become softer on boiling. The decrease produced by boiling is called “ temporary^ hard- ness,” whilst the remaining hardness is termed “ permanent.” The permanent hardness is ascertained by first boiling some of the water gently, allowing the steam to escape freely, and then, after it has cooled and the loss by evaporation has been made up with recently boiled distilled water, applying to it the soap test as before. On no accoiint must the steam from the flask be condensed and allowed to flow back into the boiling liquid, because the condensed water dissolves the escaping carbonic anhydride, ■which is thus continually returned to the contents of the flask in sufficient quantity to prevent the complete precipi- tation of carbonate of lime. ]\tany serious errors have arisen from the neglect of this precaution. The making up to the original volume, as mentioned above, is often accomplished by adding distilled water until the mixture reaches a mark on the glass indicativ^e of the previous level of the liquid; but it is more convenient to take flasks of about the same weight, and make them all up to the same weight with water (say 200 grms.) before stai-ting, and then to fill them up with the neces.sary weight of dis- tilled water at the close of the boiling. The alleged effect of soft and hard waters upon the public health has been carefully investigated; but the evidence hitherto produced, when thoroughly sifted, has only gone to show that no material difference in the death-rate of towns can be attributed to either kind of water. This subject is treated of fully in the Sixth Report of the Rivers Pollution Commissioners, pp. 184 to 201. The Commissioners, who contrasted the death-rates of towns which were as nearly as
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