B, B, which contain such a quantity of water as will make the acid of the specific gravity 1.35 to 1.42. The product in this case contains chlorine and iodic acid, and is purified by distilling from glass retorts. The chlorine passes over first, then the receivers are changed, when the pure acid comes over until only a small residue is left in the retort; this residue contains iodic acid, sulphuric acid, and sodium sulphate. Half the quantity of sulphuric acid may be used in the above processes, when neutral sodium sulphate will remain in the retort:

While this is more economical of original material, the higher heat necessary causes a greater decomposition of nitric acid and a more destructive action on the retort. The resulting sodium or potassium sulphate is more difficult to remove, as it remains as a hard, solid mass, while the acid sulphate is in a liquid condition at a moderate temperature and may be poured out.

Properties.-Nitric acid is a colorless, fuming, very corrosive liquid. When absolute, it has a specific gravity of 1.530, and commences to boil at 86°, but on account of partial decomposition into water, nitrogen tetroxide, and oxygen, the temperature rises, until at 120.5° a liquid containing 68 per cent. of the acid distils over unchanged, and has a specific gravity of 1.414 at 15°. When a weaker acid is heated, water is first given off until the acid attains the strength of the above, when it distils unchanged. Acidum Nitricum, U. S. P., has a specific gravity of 1.42, and contains 69.4 per cent. of absolute nitric acid, and closely corresponds to the commercial nitric acid.

Nitric acid is a powerful oxidizing agent. It first oxidizes most of the metals and then dissolves them, forming nitrates. Sulphur, phosphorus, and carbon are oxidized by it to oxides or acids. Many organic bodies, like turpentine, are inflamed at once on coming in contact with it, while other organic compounds are merely turned yellow. A number of substances, like cotton and benzene, undergo a process of nitration when brought in contact with the concentrated acid. In this operation the group NO, replaces hydrogen in the compound. With cotton or cellulose, gun cotton (cellulose nitrate) is formed, with glycerin, nitroglycerin (glyceryl nitrate), and with benzene, nitrobenzene.

The red fuming nitric acid differs from the ordinary variety by containing the oxides of nitrogen in solution. It is usually pre

pared by the method mentioned above, in which a quantity of sulphuric acid is used sufficient to decompose the nitre with formation of neutral sodium sulphate. The high heat necessary to carry out this process decomposes a part of the nitric acid with the formation of red fumes.

Detection.-Nitric acid is easily detected by its action on copper, which it dissolves with a blue color, giving off abundant brown-red fumes at the same time. When wool and silk are brought in contact with strong nitric acid they are colored yellow, and the color is not discharged by ammonia. The acid destroys the blue color of indigo solution, forms a dark ring when brought in contact with a crystal of ferrous sulphate and sulphuric acid, is colored red by brucine, and gives off ammonia when made strongly alkaline with potassium hydrate and heated with zinc.

Impurities and Tests.-Mineral impurities are detected by evaporating to dryness, when no residue should remain. The absence of hydrochloric acid is determined by silver nitrate, and the freedom from sulphuric acid by barium chloride. On diluting with water and adding a small quantity of solution of starch, no blue color should be produced, thus showing the absence of iodine. Iodic acid may be detected with this test by first adding some hydrogen sulphide.

Nitrates. Nitric acid is monobasic and forms with bases, by replacement of its one hydrogen atom, a series of salts known as nitrates. The most of them are prepared by dissolving the metal in the acid. In the case of the alkalies and alkaline earths, the carbonate, oxide, or hydrate is used to neutralize the acid.

The nitrates are nearly all soluble in water, the exceptions being a few of the basic salts which this acid forms. On the application of heat they evolve, first oxygen and then nitrogen tetroxide, or a mixture of nitrogen and oxygen, leaving an oxide of the metal.

PRACTICAL EXERCISES.

Place a small quantity of potassium nitrate in a test-tube, and apply gentle heat; brown, strongly acid fumes will be given off. Dilute with water and add indigo solution; the latter loses its blue color, becoming yellow or brown. This is a characteristic test for nitric acid.

Acidum Nitrohydrochloricum, U. S. P.-This substance, which is also known by the names aqua regia and nitromuriatic acid, was first prepared by Geber, who dissolved ammonium chloride in nitric acid. Basil Valentine appears to have given it the name aqua regia, and suggested the method for preparing

it, used at the present time, by mixing nitric and hydrochloric acids.

Preparation. The U. S. P. recommends the preparation of it by mixing 18 parts of nitric with 82 parts of hydrochloric acid, all by volume. They should be mixed in an open vessel, allowed to stand until effervescence has ceased, and preserved in partly filled bottles in a cool place. The compounds formed by the combination of the two acids are chlorine and nitrosyl chloride : HNO3HCl = NOCI + Cl2+ 2H2O.

Properties. Nitrohydrochloric acid is a "golden-yellow, fuming, very corrosive liquid, having a strong odor of chlorine" and a strongly acid reaction. It is wholly volatilized on the application of heat, and readily dissolves gold and platinum. This solvent action depends largely on the chlorine which is present.

Nitroxyl chloride, NOCI, is formed when a mixture of nitrogen tetroxide and chlorine is passed through a heated glass tube, and, as has already been shown, it is produced in the action of chlorine on silver nitrate. It is usually prepared, however, by heating lead nitrate with phosphorus oxychloride:

and

Nitroxyl chloride is a heavy, oily, yellow liquid which boils at 5°, is readily decomposed by water into nitric and hydrochloric acids. Nitrosyl chloride, NOCI, is formed by the union of nitrogen dioxide and chlorine :

It is also produced by the action of phosphorus pentachloride on potassium nitrite :

PCI KNO2

=

NOCI + KCl + POCIg. Being one of the products obtained on mixing nitric and hydrochloric acids, it exists in "aqua regia."

It is an orange-yellow gas, and in a freezing mixture condenses to a liquid, which fumes strongly and possesses the odor of “aqua regia." It combines with mercury, forming mercurous chloride, and liberating nitrogen dioxide; neither gold nor platinum is dissolved by it.

Nitrosyl bromide, NOBr, is prepared by leading nitrogen dioxide into bromine at a temperature of —10° to -15° as long as it is absorbed. A blackish-brown liquid results, which decomposes at -2°, giving off nitrogen dioxide, and leaving nitrosyl tribromide, NOBг, a dark, brownishred liquid.

Nitrogen sulphide, NS, is obtained in an impure condition by the action of dry ammonia on sulphur chloride or thionyl chloride. It is a

yellow crystalline powder, soluble in carbon disulphide. When heated to 135°, it sublimes, depositing yellowish-red crystals. It melts at 158° with decomposition.

There exists a similar compound of nitrogen and selenium, NgSeg.

PHOSPHORUS.

Atomic Weight, 30.96.

Valence, III.

Symbol, P. History.-Phosphorus was discovered by the alchemist Brandt, in 1669, at Hamburg. He prepared it by distilling a mixture of evaporated urine and sand. A hundred years later it was shown by Gahn to be a constituent of bones, and in 1771 Scheele published a method for preparing it from this source.

Occurrence.-Phosphorus is never found native in the free state, but chiefly as calcium phosphate, the principal constituent of bones, as well as of the minerals apatite and phosphorite. Very extensive deposits of calcium phosphate are found near Charleston, South Carolina, in Florida, and in several other of the Southern States. This "phosphate rock," as it is called, contains also some iron, alumina, carbonic acid, and fluorine. It is collected and shipped in enormous quantities to many parts of the world to be used for fertilizing purposes.

Phosphorus is, further, very widely distributed in comparatively small quantities. It is always found in plant and animal tissues, in the soil, and in sea water. The source of the element is largely bones, although a portion of that made in England is prepared from sombrerite, a mineral from the island of Sombrero in the West Indies, consisting of impure calcium phosphate.

Preparation. The bones are freed from fat by carbon disulphide or petroleum benzin, and from gelatin by superheated steam. They are then burned to whiteness. The resulting white boneash is composed of 86 per cent. calcium phosphate, Ca,(PO4), and small quantities of magnesium phosphate and calcium carbonate and fluoride.

4/2

This boneash or its equivalent, the calcined spent boneblack from the sugar refiners, or sombrerite, is treated with an equal weight of 50 per cent. sulphuric acid :

The solution of acid phosphate is decanted from the calcium sulphate, evaporated to dryness, and heated to redness, by which it loses water and is converted into calcium metaphosphate:

The calcium metaphosphate is very intimately mixed with charcoal, and gradually heated in earthenware retorts to a white heat, when the following reaction takes place :

P4 Cag(PO4)2 + IOCO.
Charcoal. Phosphorus.

3Ca(PO3)2 + 10С

=

Calcium

Metaphosphate.

Calcium
Phosphate.

Carbon Monoxide.

The yield amounts to two-thirds of the phosphorus which is The whole of the phosphorus may be recovered by

present.