8. Phosphate of Soda. If the lime contained in common water be removed by ebullition and oxalic acid, and to the strained and transparent water, ammonia and phosphate of soda be added, any magnesia present will, in the course of a few hours, be precipitated in the form of the white ammoniacal phosphate of magnesia.
9. Tincture of Galls. This is used as a test for Iron, with solutions of which it forms an inky liquor, (tannate and gallate of iron). If the test produce this effect on the water before, but not after boiling, the iron is in the state of carbonate; if after, as well as before, in that of sulphate. Tea may be substituted for galls, to which its effects and indications are similar. Ferro cyanide of potassium yields, with solutions of the sesqui-salts of iron, a blue precipitate, and with the proto-salts a white precipitate, which becomes blue by exposure to the air.
10. Hydrosulphuric Acid. (Sulphuretted Hydrogen.) This yields a dark (brown or black) precipitate, (a metallic sulphuret) with water containing iron or lead in solution.
11. Evaporation and Ignition. If the water be evaporated to dryness, and ignited in a glass tube, the presence of organic matter may be inferred by the odor and smoke evolved, as well as by the charring. Another mode of detecting organic matter is by adding nitrate (or acetate) of lead to the inspected water, and collecting and igniting the precipitate; when globules of metallic lead are obtained if organic matter be present. The putrefaction of water is another proof of the presence of this matter. Nitrate of silver is the best test for the presence of chloride of soda or common salt. By adding a small quantity of this to the common well water of New-York, a copious, white, flocculent precipitate is immediately formed, which is the chloride of soda. The same test, however, applied to the Croton water, produces no discoloration whatever.
Purification of Common water. By filtration, water may be deprived of living beings and of all suspended impurities; but substances held in solution, cannot thus be separated. Ebullition destroys the vitality of both animals and vegetables; expels air, or carbonic acid, and causes the precipitation of carbonate of lime, but the water should be afterwards subjected to the process of filtration. Distillation, when properly conducted is the most effectual method of purifying water. But distilled water is in general contaminated by traces of organic matter. The addition of chemical agents is another mode which has been proposed and practised, for freeing water from some of its impurities. Alum is often used by the common people to cleanse muddy water, and ashes and pearl-ash to destroy its hardness. When alum is used, two or three grains are sufficient for a quart of water. The alum decomposes the carbonate of lime; sulphate of lime is formed in solution, and the alumina precipitates in flocks, carrying with it mechanical impurities. This agent, however, adds nothing to the chemical purity of the water, but by converting the carbonate into sulphate of lime augments its hardness. Caustic alkalies added to lime saturate the excess of carbonic acid, and throw down the carbonate of lime, having an alkaline carbonate in solution. Professor Clark of Aberdeen,[12] (Scotland) has recently patented a plan for the purification of water, by the addition of lime. The lime unites with the excess of carbonic acid in the water, and forms carbonate of lime (chalk) which precipitates, along with the carbonate of lime held previously in solution in the water. The effect of this process is similar to that of ebullition,—as the hardness of water is, however, owing to the sulphate and not the carbonate of lime,[13] this plan can have little or no influence in rendering hard water soft. Alkaline carbonates soften water, decompose all the earthy salts (calcareous and magnesian carbonates, sulphates, and chlorides) and precipitate the earthy matters. They leave, however, in solution, an alkaline salt, but which does not communicate to water the property of hardness.
Sea-water includes the waters of the ocean and of those lakes, called island seas, which possess a similar composition. The Dead Sea, however, varies so much from ordinary sea-water, as to rank amongst mineral waters.
The quantity of solid matter varies considerably in the waters of different seas, as the following statement proves—
| 10,000 parts of water of | Solid constituents. | |
| the Mediterranean Sea, contain | 410 grs. | |
| English Channel, | 380 „ | |
| German Ocean | { At the Island of Fohe, | 345 „ |
| { At the Island of Norderney, | 342 „ | |
| { In the Frith of Forth, | 312 „ | |
| { At Ritzebuttle, | 312 „ | |
| At Apemalle, in Sleswick, | 216 „ | |
| At Kiel, in Holstein, | 200 „ | |
| Baltic Sea | At Doberan, in Mecklenbergh, | 168 „ |
| At Travemunæ, | 167 „ | |
| At Zoppot, in Mecklenbergh, | 76 „ | |
| At Carshamm, | 66 „ | |
The average quantity of saline matter in sea-water is 3½ per cent., and its specific gravity about 1.0274. The composition of sea-water differs also in different localities. Iodine has been found in the Mediterranean sea.
Action of Water on Lead. When lead is exposed to atmospheric air, the oxygen of the air combining with it, forms an oxide, while, at the same time the carbonic acid of the air, unites with it forming a thin white crust, which is the carbonate of lead. This formation is accelerated by moisture, and by the presence of an unusual quantity of carbonic acid in the atmosphere. The same process goes on with still greater rapidity in pure running water. But if water be deprived of all its gases by ebullition, and excluded from contact with the air, the lead will not be acted upon If water, however, be exposed to the air, although all the gases have been expelled, a white powder will soon form around the lead, till, in the course of a few days, there is formed a large quantity of white, pearly scales, which partly float in the water, but are chiefly deposited on the bottom of the vessel. In 12 ounces of distilled water, contained in a shallow glass basin, loosely covered to exclude the dust, twelve brightly polished lead rods weighing 340 grains, will lose 2½ grains in 8 days, and the lead will show evident marks of corrosion; and this action will go on as long as the water is exposed to the air. While these changes are going on, a small quantity of lead will be dissolved, as may be shown by carefully filtering the water acidulating with a drop or two of nitric acid, and evaporating to dryness. Sulphuretted hydrogen is also a good test, occasioning, where lead is present, first a brown color, and subsequently a black precipitate. Christison has proved that the lead which is dissolved, is in the form of the carbonate, and hydrate of the oxide, or, oxide of lead, carbonic acid and water.