The Condition of Water in Nature.

Rainwater contains all the substances present in the air in dissolved form, such as oxygen, nitrogen, carbonic acid, and sometimes traces of nitric acid, ammonium carbonate, or ammonium nitrate. These latter salts are found mainly in rainwater from thunderstorms. The first rainwater also contains foreign matter: dust suspended in the atmosphere. However, carefully collected rainwater is often very pure and can replace distilled water in most chemical operations.

Water from rivers, streams, springs, and wells is less pure than rainwater. It contains chlorides, sulfates, and carbonates of lime and magnesia, and sometimes of soda, potash, and alumina. The composition of these waters varies with the nature of the ground through which they have passed. They are usually acceptable for drinking and cooking vegetables and have no noticeable taste. In this case, they are called soft water or drinking water.

Sometimes, however, water is unsuitable for cooking vegetables and washing with soap; it is then described as hard or raw.

Soft water leaves only a very small residue upon evaporation, retains its transparency when boiled, and is clear and tasteless; it dissolves soap, or at least forms only a very small precipitate in soap solutions.

The poor quality of hard water must be attributed to the presence of calcium salts. It forms clumps with soapy water and cannot be used for all household purposes.

Hard water is divided into two different types:

Water described as “selenitic”; most of the lime is in the form of sulfate. This is the case with water from wells in Paris, which is sometimes saturated with calcium sulfate (gypsum). It does not become cloudy when boiled and forms abundant precipitates with ammonium oxalate and barium chloride.

The second type of hard water contains calcium carbonate dissolved through an excess of carbonic acid. It turns a logwood solution blue and becomes cloudy when boiled, exposed to air, or treated with limewater. It is made suitable for drinking and household use:

1. By boiling it briefly and then letting it stand (the excess carbonic acid, which dissolves the calcium carbonate, is released, and the calcium carbonate precipitates)
2. By agitating it in contact with air, which also causes the excess carbonic acid to be released and the calcium carbonate to settle
3. By treating it with limewater until it no longer forms a precipitate with this reagent. In this case, calcium bicarbonate is converted into insoluble neutral calcium carbonate: CaO2CO² + CaO = 2 (CaOCO²).

Selenitic water can be made, if not suitable for drinking, at least suitable for cooking vegetables and washing with soap, by adding a sodium carbonate solution: CaOSO³ + NaOCO² = NaOSO³ + CaOCO².

This reaction produces insoluble calcium carbonate and sodium sulfate; the latter salt, although soluble in water, poses no problem in most industrial operations.

Soap can be used to make selenitic water suitable for washing with soap. A small quantity of soap is enough to precipitate all the lime as insoluble calcium margarate, stearate, and oleate; once these precipitates have formed, the soap dissolves without decomposing.

The waters considered the purest are those of torrents flowing down from granite mountains.

To detect the presence of calcium bicarbonate dissolved in water, Dupasquier proposed using an alcoholic tincture of campeche wood. The yellow coloring matter of this wood turns violet when the water contains even the slightest trace of calcium bicarbonate. This characteristic is generally sufficient for testing drinking water, in which potassium or sodium bicarbonate is never or almost never found. However, since these latter salts also turn the campeche wood solution violet and could occur incidentally in water, a few drops of calcium chloride are added to the water, forming a precipitate only if the water contains potassium or sodium bicarbonate.

The presence of silica and alkaline silicates has been reported in some drinking water. Derville found that silica is one of the consistently present constituents of water used for drinking: he reported substantial amounts of it in water drawn from the Loire during flooding.

Nitrates are sometimes found in ordinary water, especially in water from wells in large cities.

Upon evaporation, drinking water leaves a residue whose weight generally does not exceed 1 to 3 decigrams per liter. This residue consists mainly of calcium carbonate, calcium sulfate, and calcium chloride.

Seawater contains approximately 42 grams of salts per liter, of which sea salt accounts for 26 or 27 grams.