1. A few drops of tincture or infusion of nut galls turns water containing iron, black; when this takes place, both before and after the water has been boiled, the metal is present under the form of sulphate of iron.

2. A few drops of a solution of ferrocyanide of potassium (solution of prussiate of potash) gives a blue precipitate in water containing sesqui salts of iron; and a white precipitate turning blue by exposure to the air, in water containing a proto salt of iron. From the intensity of the color the quantity present may be inferred. Water is readily impregnated with iron by throwing into it a few rusty nails, hoops, or other similar objects, or if it comes in contact with such substances by connection through iron pipes. The amount of iron dissolved by water in passing through iron pipes is exceedingly small. It has been shown that water containing organic matter is purified to a large extent of the contamination by a passage through iron pipes, but even the presence of a substance such as iron, known to produce beneficial effects when administered medicinally, is much to be deprecated in water for every-day use, and is undesirable in water used for the manufacture of mineral waters, as it has a deleterious action upon flavors used in the preparation of the beverage and in some cases entirely destroys it.

It is not often that a water is found which contains enough iron to be prejudicial to health. Some authorities say that there ought not to be more than two-tenths grain per gallon, and others think that water containing one-half grain per gallon is not injurious. Iron is detected by means of sulphide of soda and hydrochloric acid. If no lead is present, the color produced by the sulphide must dissolve completely on the addition of two or three drops of acid.

If it be desirable to learn whether there is more than half a grain of iron in a gallon of any water, dissolve one ounce avoirdupois of sulphate of iron (copperas) in eleven ounces of water. Each drop of this solution contains about one sixty-fourth grain of iron. Add one drop of the solution to four ounces of pure water, which will then contain iron at the rate of about one-half grain per gallon. Add to this a drop of sulphide of soda, and compare the color with that of the water in question.