Chlorine.—Tests: Nitrate of silver (twenty-five cents a drachm), twenty-four grains to one ounce of distilled water, and dilute nitric acid (ten cents an ounce). Pour a few drops of each into the suspected water. If chlorine is present, there will be a cloudy-white precipitate of chloride of silver, which will gradually turn darker. One grain of chlorine to a gallon of water gives a haze; four grains a marked turbidity, and ten grains a considerable precipitate. In case chlorine is found, and any particular source is suspected, a pailful of salt (chloride of sodium) and water may be thrown into the place from which the leakage is supposed to come, and the water again examined, after a few hours, to see whether the amount of chlorine has increased.
Nitrates.—Tests: Pure sulphuric acid and a saturated solution of sulphate of iron (copperas). Add an equal bulk of the acid to any quantity of the water in a test-tube. The mixture will become very hot. Wait until it is cool, and then pour in the iron solution gently, so that it will float above the mixed acid and water. If nitrates are present, there will be an olive-colored layer where the fluids meet.
Nitrites.—Test-mixture: Iodide of potassium (fifty cents per ounce), one part; starch, twenty parts; water, five hundred parts. Make the starch-solution first, and filter when cold; then add the iodide of potash. Add to the suspected water this mixture, and then a little dilute sulphuric acid. If nitrites are present, there will be an immediate blue color.
Organic Matters in general.—Test: Eight grains of chemically pure permanganate of potash in one ounce of distilled water. In half a pint of the suspected water in a tumbler, put one drop of the solution. If the red color disappears in one half hour, add more. For every drop that loses color in the half-pint there will be found one and a half to two grains of putrid organic matter in a gallon of the water. If the action is rapid, the matter is probably animal; if slow, vegetable.
To purify such water, if it must be used, drop in the solution until a slight red tinge remains. The organic matter is then all oxidized and rendered harmless. It is better, however to boil such water before using it for drinking.
Precautions with regard to Drinking-Water.
Do not drink water that has been standing long in lead pipes, or lead cisterns or tanks.
Filter it before drinking.
See that the current of ground-water in the well from which you get your drinking-water is from the well toward any possible source of contamination (privy-vault, cesspool, etc.), and not vice versa.
If the use of a suspected water is unavoidable, boil it first. It can be rendered palatable by an infusion of tea or coffee.