The solvent power of water is very large. As a rule hot water dissolves larger quantities of solid matter than cold. Water is found in nature in many forms — vapor, dew, boar-frost„ rain, hail, snow; besides the several distinct variations of spring water, well water, river water, surface water, sea water, etc. As has been mentioned it is never found in a state of purity. Analyses of dew and hoar frost show from 264 to 8.00 parts of solid impurities in 100,000 parts of water. These are organic car bon, organic nitrogen, ammonia, nitrates and nitrites, chlorine, lime and magnesia. These substances have been held in solution in the vapor of water in the air. Snow will gain in ammonia content the longer it lies on the ground.
Rain water, when collected before it touches the earth, contains only such impurities as may be derived from the atmosphere, chiefly con sisting of oxygen, nitrogen and carbon dioxide, with more or less nitric acid and ammonia in the case of thunder showers. The rain water of towns contains comparatively large quantities of sulphurous and sulphuric acids and of soluble salts. The amount of these substances may be taken as an estimate of the comparative purities of the atmospheres of different towns. Rain water collected near the sea is rich in chlorides. Samples of rain water taken in a farming country near the sea have shown 42.8 parts of solid impurities per 100.000.
River water varies greatly in so far as the nature and quantity of the substances held in solution by it are concerned. The soluble con stituents of river water are chiefly such as may be derived from the rocks through which the water of the springs which have fed the river has percolated and the amount of surface water it has received owing to storms. The dilution of the original spring water by the continual influx of tributaries reduces the relative quan tity of solid matter held in solution. while the escape of carbon dioxide during the ex posure of the surface water to the air causes the precipitation of those salts which were held in solution by the aid of the carbonic acid. River water is often largely contaminated by the drainage of towns or of manufactories situated on the river banks.
Spring Waters.— The soluble constituents of sprang waters are various. In some springs the quantity of dissolved solid matter ts but trifling, while in others it amounts to 2.000 grains per gallon. Spring waters are usually di vided into classes in accordance as one or other dissolved constituent predominates. See M 1 N MAL WATERS.
Sea water is essentially an alkaline chlori nated water. The quantity of solid matter held in solution varies in the waters of different seas. Inland seas, as a rule, contain less solid matter than the ocean; thus the solid content of the water of the Black Sea amounts to about 1.760 parts per million, while that of the Baltic averages 17.700. and that of the Atlantic Ocean 36,000 parts per million. The -ubstances held in solution in sea water are chiefly chlorides and sulphates of sodium, magnesium and potassium, together with iodides, bromides and carbonates, chiefly of potassium and calcium Use of Water.— In considering the suitable ness of a water for domestic use attention should be principal'y paid to (I) the source of the supply, (2) the total solid matter held in solution by the water, (.3) the organic mat ter held in solution and (4) the action which is likely to be exercised on the water by the means of supply. In examining the source of a water supply attention should be paid espe cially to the proximity of drains or sewers of any description, and to the likelihood of con tamination from these sources. The nature of the soil through which the water percolates should also be inquired into. The solid sub stances held in solution by a sample of water may be estimated by evaporating a measured quantity of the water to dryness in a platinum basin heated by steam and weighing the resi due. From a knowledge of the total solids in a water, unaccompanied by any further infor mation, no reliable conclusion as to the suit ability of such a water for potable purposes can be deduced. In seeking to determine whether a sample of water has undergone contamina tion with hurtful organic matter the following points are to be more particularly attended to: (1) Estimation of the amount of chlorine, whether existing as hydrochloric acid or as a chloride; (2) estimation of ammonia; (3) es timation of nitrates, and (4) detection and estimation, if necessary, of poisonous metals, The presence of an undue amount of chlorine generally points to contamination with animal matter. Pure waters do not as a rule contain more than three to four grains of chlorine per gallon. It must, however, be borne in mind that such waters as flow through a soil rich in Cilorides— such, for instance, as the waters found in the neighborhood of salt-beds— al ways contain large quantities of chlorine. The sudden appearance of chlorides in a water previously free or nearly free from these sub, stances points to animal contamination.