On food : Being lectures delivered at the South Kensington Museum / by E. Lankester.

  • Lankester, E. Ray (Edwin Ray), Sir, 1847-1929.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: On food : Being lectures delivered at the South Kensington Museum / by E. Lankester. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    34/408 (page 24)
    Another substance of some impoi'tance in water is tlie chloride of sodiunij or common salt, which can only be accounted for in our surface-well waters by the fact of the salt being constantly used by man in cooking, &c., and thus passing into the drains and sewers, is washed into the wells. When we find this substance in waters, we should be careful of using them dietetically. The best test for chloride of sodium is nitrate of silver. It throws down the chloride in the form of a- chloride of sUver. It is a creamy-looking precipitate, at first white, and gradually becomes bluish-black by the agency of light. It is, in fact, one of the salts used by the photographer to produce his pictures on paper. I might continue these illustrations, but I hope I have shown you sufficient to indicate that a very little chemistry will enable an intelligent person to detect whether water contains large quantities of the more common impurities of water. There is another method of extracting approxima- tively the quantity of saline impurities in water. If we take a quantity of water and boil it in an evaporat- ing basin, the water will at last entirely disappear, and the inorganic matters will be left at the bottom of the vessel. By taking two or three waters, and thus treat- ing them, we can judge, within a little, of theii* relative amount of impurity. We may judge also to some extent, by this test, of the quantitj'^ of organic matters present in water; for, according as these are present, will the precipitate be of a dark and dirty colour. You must not suppose, however, that the saline im- purities I have mentioned are all that are to be found