Marsh Water. This is analogous to lake water, except that it is altogether stagnant and is more loaded with putrescent matter. The sulphates in sea and other waters are decomposed by putrefying vegetable matter, with the evolution of sulphuretted hydrogen; hence the intolerable stench from marshy and swampy grounds liable to occasional inundations from the sea. Marsh water cannot be drunk with safety either by man or beast.
Tests of the usual impurities in Common Water.
The following are the tests by which the presence of the ordinary constituents or impurities of common waters may be ascertained.
1. Ebullition.—By boiling, air and carbonic acid gas are expelled, while carbonate of lime, (which has been held in solution by the carbonic acid) is deposited. The latter constitutes the crust which lines tea-kettles and boilers.
2. Protosulphate of Iron. If a crystal of this salt be introduced into a phial filled with the water to be examined, and the phial be well corked, a yellowish-brown precipitate (sesquioxide of iron) will be deposited in a few days, if oxygen gas be contained in the water.
3. Litmus. Infusion of litmus or syrup of violets is reddened by a free acid.
4. Lime Water. This is a test for carbonic acid, with which it causes a white precipitate (carbonate of lime) if employed before the water is boiled.
5. Chloride of Barium. A solution of this salt usually yields, with well water, a white precipitate insoluble in nitric acid. This indicates the presence of sulphuric acid (which, in common water, is combined with lime).
6. Oxalate of Ammonia. If this salt yield a white precipitate, it indicates the presence of lime, (carbonate and sulphate.)
7. Nitrate of Silver. If this occasion a precipitate insoluble in nitric acid, the presence of chlorine may be inferred.