Minerals derived from the soil. Impure waters predispose to disease.

with soluble salts, these will be found abundantly in the water of the wells. If the soil contains carbonate of lime, that salt will be found in solution in the water, combined with an excess of carbonic acid. If pyrites of iron occur in the soil, then sulphate of iron will be found in the springs; and if carbonate or any other salt of lime also occurs, we shall have also sulphate of lime dissolved. Vegetable matter is generally found in the water in the state of an extract, consisting of ulmine or geine. Animal matters are found in a putrescent state, with many animal acids and ammoniacal salts. It is notorious that the dreadful scourge called the Asiatic cholera, a disease which has travelled over the world, selected for its favorite abodes those cities which were founded on the tertiary limestone, where the water is known to be charged with an abundance of carbonate of lime-a salt that is known to derange the functions of the alimentary canal when it is drank. Most strangers who visit the Western States have experienced inconveniences arising from this cause. The water of Paris and of Vienna is also known to be charged with the same impurities, and produces the same effects.

Now the countries I have mentioned are the very places where the cholera produced the greatest havoc, and where it remained for the longest time. Cholera is considered an epidemic disease; and those causes which I have mentioned were peculiarly calculated to act as predisposing and exciting causes of the disease.

When an epidemic disease prevails, we should endeavor to ascertain and avoid the remote causes which may induce it, and thus diminish the danger to which we are exposed. A knowledge of the geology of a country, and the nature and distribution of water, may often serve as guides. Every physician certainly ought to be acquainted

Importance to physicans.

Tests for the impurities in water.

with this subject, for he may otherwise send his patient into the midst of danger, when he intends to remove him far from it.

In order to detect the impurities existing in water, the following tests may be used, which will give an approximate idea of the relative impurity of the water in question. If the substances are to be separated from each other and quantitatively estimated, it can only be done by an experienced chemist. The tests indicating the nature of the foreign matters and the estimation of their gross amount, are, however, easily applied.

In order to form an estimate of the quantity of foreign matter in the water, its specific gravity may be taken as before described. Then, according to Kirwan, “subtract from this number the specific gravity of pure water, and multiply the remainder by 1.4. The product is equal to the saline conten s in a quantity of the water, denoted by the number employed to indicate the specific gravity of distilled water."

To ascertain the correctness of this operation, evaporate 10,000 grains of the water to dryness, and weigh the residue.

The test for muriates, or chlorides in solution, is a solution of nitrate of silver in distilled water. If any muriate or chloride is present, a white precipitate will be formed by this test, consisting of chloride of silver.

If no immediate precipitate takes place, expose the solution to the action of sunlight. If it becomes bright red, and a bistre brown precipitate takes place, ulmine is present. If it turns black, animal matter is present.

To detect the presence of any free acid, use a slip of blue litmus paper, which will be turned red if any free acid is present. Boil the water, and if, after boiling, it ceases to redden litmus paper, the acid was the carbonic

Tests for sulphates and nitrates.

Hard and soft water.

acid. If it still reddens the blue paper, the acid is of a fixed nature, and is to be examined by the tests for sulphuric, muriatic and nitric acids.

To detect sulphuric acid or any sulphate, use a solution of muriate, or acetate of barytes; if these substances are present, a white precipitate will form. Muriatic acid will be indicated by the test of solution of nitrate of silver. Nitric acid may be discovered by evaporing the water to small bulk, then adding a particle of gold leaf and a drop of muriatic acid; the gold will be dissolved if nitric acid is present. If nitrates exist in the water, they will be discovered by evaporating the water to dryness and throwing the solid mass obtained on burning charcoal. If deflagration take place, it indicates the presence of ni

trates.

In order to discover if lime exist in the water, test a portion of it by means of oxalate of ammonia. A white precipitate indicates lime.

To discover iron, drop into the water a little of the solution of ferrocyanate of potash. If iron is present, a blue precipitate will form. A decoction of nutgalls may be used in its stead, and then a black precipitate will ensue.

Salts of soda may be detected by evaporating some of the water to dryness, and heating some of it in a piece of platina foil in the flame of the blow-pipe. If it color the flame yellow, soda is present. Salts of potash are detected by evaporating a portion of the water to small bulk, and then dropping into it muriate of platina. A yellow precipitate indicates potash.

In order to decide the question whether the water is "hard" or "soft," we have only to make a solution of castile soap in alcohol, turning off the clear portion for use, then to add some of this tincture of soap to the water. If no turbidness ensue, and no flocculent precipitate take

Mineral springs.

Chalybeate waters.

place, the water is soft and fit for washing; but if the water gives a copious flocculent precipitate, it is hard and not suitable for this purpose.

By means of these tests all the usual questions respecting the purity or impurity of water may be solved, in a manner sufficiently accurate for ordinary purposes.

Mineral springs, or saline waters, would constitute an interesting subject for discussion, but we have not at present either time or room for their full consideration, and shall therefore take a hasty view of them.

Mineral waters are sufficiently abundant in our country, and are found to be extremely valuable in the cure of certain derangements of the digestive organs, and in scrofulous diseases of the system. The most remarka⚫ ble springs of this character contain sensible proportions of iodine and bromine, in the state of hydriodates and hydrobromates of soda and magnesia, to which substances perhaps they owe chiefly their anti-scrofulous action, while the free carbonic acid, and the carbonates of soda and magnesia, give them a mild and salutary action on the digestive organs. Mineral waters will not, however, serve for ordinary use as drink, but are to be considered as medicines; and their use should be regulated by the advice of skilful physicians; otherwise they are liable to do injury, as not unfrequently happens, where they are drank injudiciously, and in great quantity. This must evidently be the case, if the waters possess any marked action on the system.

Chalybeate waters are those which are charged with carbonate and sulphate of iron. They are powerfully tonic, and are, under favorable circumstances, and where there is no inflammation of the mucous membrane of the stomach, of great use in the cure of dyspepsia, and other derangements of the system arising from debility.

Sulphur springs.

Salt springs.

Sulphur springs are generally charged with sulphuretted hydrogen gas and carbonic acid, and contain hydrosulphates of soda, potash, lime, &c., besides carbonates of the same bases, and carbonate and sulphate of iron. Although they have a very unpleasant odor, (like that of rotten eggs,) persons who have become habituated to them like their flavor, and become strongly attached to their use. Such waters are highly active on the system, and are efficient when used externally and internally, in the cure of chronic rheumatism, some cutaneous diseases, and certain scrofulous tumors. Their use, like that of all other mineral waters, should be regulated by the advice of physicians, who should be well acquainted with the composition of the waters in question, and their action on the system.

Salines, or salt springs, are sources of water charged with large quantities of chloride of sodium in solution. They are found abundantly in the western parts of our country, as in New York, Ohio, Pennsylvania, and along the whole range of the Allegany mountains, in various. places. They are especially valuable in the western country, as sources from whence an abundance of salt may be obtained. They are frequently found in the immediate vicinity of coal mines, which supply fuel for the evaporation of the water, by which means the salt is obtained.

The full consideration of this subject should form a separate essay. What I have now presented may serve as an outline of a more elaborate report on some future occasion.

Pure water is a fluid of such great importance to mankind, that I deem it expedient to devote the few remaining pages of this Tract to its consideration. It is very difficult to obtain water absolutely pure; but nature presents it to us