Ammonia may be obtained from most waters by distillation after the addition of a little sodium carbonate; when the whole of this am monia has been driven off it not unfrequently happens that the addition of an alkaline solu tion of permanganate of potassium and heating results in the production of a further quantity of The ammonia obtained by the first distillation is usually spoken of as ((free am monia,' while to that obtained by the second distillation the name of *albumenoid ammonia* is given. The presence of even small quanti ties of albumenoid ammonia points unmistak ably to organic contamination. Such ammonia is derived from the decomposition, by the agency of the alkaline permanganate liquid, of nitrogenous matter of animal or vegetable ori gin. Pure water should not contain more than 0.10 parts of *free" ammonia per million, nor more than 0.08 parts of *albumenoid" per mil lion.
If nitrogenous matter has become thoroughly oxidized it gives rise to the formation of nitric and nitrous acids. The presence of these acids or of their salts, therefore, generally points to previous contamination of some organic nature. As, however, these things are the harmless that is, in the quantities in which they occur in waters—products of the decomposition, and, therefore, of the removal, of hurtful substances, their presence, even when in comparatively large quantities ought not of itself condeaut a water. The poisonous metals which are most likely to occur in drinking waters are lead, And copper, These may be easily detected and esti mated even when present in exceedingly minute quantities. For details of the analytical methods of water analysis reference must be made to manuals of applied chemistry. It is evident that
in a water analysis we look for symptoms of a disease; not for substances which are in them selves hurtful, but for substances whose pres ence is associated more or less invariably with others, the action of which upon the system cannot but be pernicious.
In storing water for domestic purposes the water may undergo contamination from the essels containing it or from proximity to drains or other places emitting noxious gases. It is certain that water exercises a solvent, action upon lead; but our ordinary leaden water pipes and tanks become coated with a comparatively insoluble compound of lead, so that the danger of contamination from this source is net great. Hot water should never be stored in leaden tanks; it very quickly corrodes and dissolves the metal. Aerated waters act rapidly on lead; for this reason they should never be prepared or stored in leaden vessels. The solvent action of water on copper is very small. The system of storing Water for drinking or cooking in cisterns close to, or even communicating with, the house drainage system, is a very bad one.
(See SANITARY SCIENCE; PUBLIC HEALTH).
In sotne circumstances, as in the case of swim ming-baths, large quantities of water have to be heated to a certain temperature and kept at the same for a considerable time while the water has to be maintained in a due condition of purity. For industrial purposes also most waters require purification of a kind, depending upon the processes of manufacture in which they are employed. The most common treat ment is that known as °softening," for the re moval of lime and mapesia carbonates, chlorine and other lesser impurities. See WA it Sorrell nyc: WATER( SUPPLY.