In works on hygiene which are exclusively intended for professional readers it is usual to describe the processes, both chemical and physical, for the analysis of water for the purpose of ascertaining what constituents are present which may exercise any injurious action on the animal which drinks it.

Stonewort (Chara fragilis).

Fig. 483. - Stonewort (Chara fragilis).

1, Plant. 2, Sporangium and anther-idiutn. 3, Valve of antheridium. 4, Enlarged branch. 5, Section of sporangium. 6, End of a filament.

By the mere physical examination the general character of the water is determined by the unaided eyesight, but it must be understood that this kind of examination does not justify any conclusion as to the qualities of the water which may render it fit or unfit for use. It has been proved that some of the brightest water may be charged with deadly material. In one of the outbreaks of cholera which occurred in London, a certain pump, to the water of which several serious outbreaks of cholera were traced, was so noted for its bright, and sparkling, and palatable character that all the people within a reasonable distance round it came regularly to obtain, at any rate, sufficient water for drinking purposes, and as a consequence the disease was widely spread. As a matter of course, as soon as the character of the water was discovered, the pump was closed, and the spreading of cholera from that source was arrested. An illustration in the opposite direction was afforded by an examination of the porter-coloured water which is so commonly noticed in ponds near straw-yards, such ponds being the ordinary drinking-places for horses and cattle. The brown-coloured water is commonly said to suggest the presence of sewage, but the water referred to in the farm ponds was repeatedly examined by Dr. Augustus Voelcker, and found by him to be singularly free from organic contamination, the brown colour being due to the formation of humic and ulmic acids which did not appear to exercise any deleterious influence on the animals which drank of it. There can be no doubt that the water of these farmyard ponds, into which the drainage from the straw-yards is constantly running, must have received large quantities of organic matter; but, being at the same time perfectly open to the constantly moving atmosphere, the organic matter must have been oxidized into comparatively innocuous compounds.

It is not suggested, of course, that porter-coloured water is a desirable fluid for horses or cattle, nevertheless it is an undoubted fact that it was in former times the habitual drink of those animals year by year; and in one case in the writer's knowledge it continued for a dozen years on a large farm, where the stock remained during the whole of that time in a remarkably healthy condition. It was during this period that the two circumstances, i.e. the remarkably healthy condition of the stock on the farm and the habitual use of porter-coloured water for the horses and cattle - in the case of the latter the invariable use of it for the reason that there was no other water within the animals' reach, - attracted Dr. Voelcker's attention and led to the analyses referred to. The story itself suggests that a chemical examination of discoloured water is necessary in order to determine on what the discoloration depends. But, in any case, it must be clearly understood that the colour in itself is not a satisfactory indication of the quality of the fluid.

The brightest and most sparkling water may be absolutely deadly, while dark-coloured and dirty water may be comparatively harmless.

A rough test, which the unprofessional observer can easily employ, is to allow the specimen of water to stand in a glass for some hours, for the purpose of ascertaining if there is any sediment. Taste and smell are means of ascertaining something of the qualities of water, as in a wholesome state the fluid does not possess any decided taste, either acid or alkaline; and an odour, either pungent or offensive, may be at once accepted as proof that the water is not fit for drinking purposes. Then there are also certain simple tests which may be readily employed even by a person who has not more than a very elementary knowledge of chemistry. For example, the presence of lime may be detected at once by adding a solution of oxy-late of ammonium, which causes at once a white precipitate, and some idea may be formed of the amount by the quantity of precipitate which falls. A mere turbid condition, rendering the water somewhat opalescent in appearance, does not indicate that the water contains more than an ordinary quantity of lime, while a large quantity of precipitate indicates a hard water.

Colonel Fred. Smith gives a very simple process, which he has found effectual in estimating in a rough way the amount of hardness of water in which the oxylate of ammonium has caused the characteristic white precipitate. He proposes to use the ordinary soap liniment as a test, and he finds that 1 drop of this preparation added to oz. of water will indicate about 1 grain of lime per gallon, if on shaking the mixture a lather is produced.

If, however, 4 drops are required to produce a lather there will be about 6 grains of lime per gallon. If 6 drops are required there will be 9 grains, if 12 drops, 18 grains. Calculating that the amount of lime per gallon in good water should not exceed 6 grains, it is easy to form some idea of the degree of hardness which exists in the water under examination. The process may be further extended in order to ascertain which of the lime salts is the cause of the hardness; which may depend upon carbonate of lime, and indeed generally does, but may also result from the presence of a sulphate, chloride, or nitrate. The presence of the carbonate is determined accurately by boiling a portion of the water which has been tested by the soap liniment. Supposing that it takes 12 drops of soap liniment to produce a lather before boiling, and only 3 drops to produce the same effect after the water has been boiled, it would show that the hardness was due to chalk (calcium carbonate). The advantage of acquiring this knowledge will be obvious when it is remembered that the hardness caused by the carbonate of lime may be got rid of by a comparatively simple process (the addition of a small quantity of lime, and precipitation of the carbonate. See page 123), while that caused by the presence of sulphate, chloride, and nitrate of lime cannot be removed. The test, however, for chlorine, sulphuric acid, and nitric acid would be rather beyond the powers of the amateur.

The presence of organic bodies is generally considered to render water unfit for use, but a great deal must depend upon the nature of the organic matter, whether animal or vegetable, and also on the state of decomposition which has been reached. Samples of water which have been found to contain an enormous quantity of vegetable matter have been taken by animals with perfect impunity, doubtless on account of the matter being of vegetable origin, and not having undergone decomposition. Microscopic examination of water, especially water which deposits various impurities after rest, is the only satisfactory method of discovering the character of the impurities. A further step in the same direction is inoculation of nutritive media, such as pure gelatine and other similar subtances used by the bacteriologist, but this, as well as the use of the microscope, must necessarily be left in the hands of the expert.