SECTION II.-The nitrites, nitrates, hypophosphites, phosphites, phosphates, arsenites, arseniates, antimoniates; sulpharsenites, sulpharseniates, sulphantimoniates.

SALTS OF THE ACID-RADICALS WHICH CONTAIN NITROGEN, PHOSPHORUS, ARSENIC, AND ANTIMONY COMBINED WITH OXYGEN OR SULPHUR.

Of acid-radicals containing nitrogen combined with oxygen, two only are of sufficient importance to demand attention; these are the nitrous and the nitric radicals (NO, and NO,): several other compounds of nitrogen and oxygen exist, but are of trivial importance in an analytical point of view.

SALTS OF THE NITROUS RADICAL, OR NITRITES.

This radical is usually obtained in combination with potassium by heating the nitrate of potassium (KNO,) in a crucible, by which means the nitrite (KNO,) and oxygen are produced. Nitrites detonate when heated with combustible bodies; they are either colourless or yellow, and generally crystallizable: the nitrite of silver is almost the only insoluble salt. This radical appears to have the property of assuming oxygen and transforming itself into monobasic, bibasic, and tribasic radicals, after the manner of the phosphoric acid-radical.

THE HYDROGEN SALT (HNO,), or nitrous acid, is known only in solution in water, forming a blue liquid; its anhydride (NO) is obtained as a gas when 1 part of starch is heated with 8 parts of nitric acid of specific gravity 1.25: if the vapour is first dried by chloride of calcium, and then passed through a tube cooled to -20° C., a very volatile liquid is obtained, green at the ordinary temperature, but colourless when exposed to extreme cold; the vapour of this body is yellowish red.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, MAGNESIUM, IRON, and COPPER SALTS of this radical are soluble.

The Silver Salt is obtained by adding nitrate of silver to a soluble nitrite (as the potassium salt); it is a yellowish white crystalline precipitate, the formula of which is probably AgNO.

It requires 300 parts of cold water for its solution, but is more soluble in hot water; and from its hot solution it crystallizes on cooling. It is insoluble in alcohol.

THE MERCURIC SALTS are of doubtful existence; and the LEAD SALT is soluble.

This radical is also detected by the following experiments:-

a. By its liberation, even by weak acids (as acetic acid), in the form of the hydrogen compound, and the instantaneous decomposition of the latter, with formation of nitric oxide gas, which reddens on contact with air.

B. By the addition of a solution of ferrous sulphate and sulphuric acid to the solution of a nitrite, a deep red liquid is obtained.

y. Nitrites, when added to solutions of auric chloride or mercurous nitrate, cause the precipitation of gold or mercury; from solutions of manganous or ferrous salts, they precipitate manganic or ferric hydrate.

d. When to a solution containing pure sulphuric acid, iodide of potassium, and starch, a minute portion of a nitrite is added, the characteristic blue iodide of starch is at once produced.

SALTS OF THE NITRIC RADICAL, OR NITRATES.

The abundant forms in which this radical occurs are its potassium, sodium, and calcium salts; they are produced whenever nitrogenized organic matter is allowed to decompose in the presence of the hydrates of those basic radicals. Nitrates in general have a peculiar cooling taste; they are all decomposed at a red heat: some, as the alkaline nitrates, yield nitrites in the first place; but ultimately all are converted into oxides, with evolution of nitrogen and oxygen. Nitrate of ammonium (NH,NO,) undergoes a peculiar decomposition under these circumstances, water and the gas called nitrous oxide (NO) or laughing-gas being formed:

NH, NO1=2H20+N ̧0.

Nitrates when fused on charcoal deflagrate, their oxygen uniting with the carbon to form carbonic acid gas, which then

takes oxygen, and converts the metal into a carbonate, if that salt is capable of withstanding the temperature to which it is exposed. When heated before the blowpipe with carbon and sulphur, with carbon and phosphorus, or with cyanide of potassium, a very violent and dangerous detonation ensues.

THE HYDROGEN COMPOUND (HNO1), or nitric acid, is an exceedingly corrosive liquid, and forms a most powerful solvent for metals, by reason of its ready decomposability. When acting as a solvent, however, it differs from most acids hitherto considered, which simply part with their hydrogen and receive the replacing molecule of metal: nitric acid undergoes a more radical change; for so comparatively feeble is the affinity which the nitrogen has for its 3 equivalents of oxygen, that the hydrogen of the acid in escaping decomposes a part of the acid-radical with the formation of water and the evolution of one of the gaseous lower oxides of nitrogen. Thus, when it acts upon copper

8HNO,+6Cu=6CuNO,+N,O,+4H,O.

nitric oxide.

This property it is which imparts such a peculiar energy to the mixture of nitric and hydrochloric acids known by the names nitrohydrochloric acid and aqua regia: the oxygen of the nitric radical unites with the hydrogen of the hydrochloric acid; and among other products of decomposition, chlorine is set free, and, like all other nascent elements, exerts upon the body submitted to its action the most powerful effect:

2HNO,+2HCl=2H ̧0+N,0,+201.

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In this way it is that this mixture of acids will dissolve the precious metals gold and platinum, which are attacked by chlorine, although not affected by either hydrochloric or nitric acids separately. The same reaction of course takes place when either hydrochloric acid is added in excess to a nitrate, or nitric acid in excess to a chloride; for

2MNO,+4HC1 =2MC1 +2H ̧0+N ̧0 ̧+2C1

or 2MC1 +4HNO,=2MNO,+2H ̧0+N20,+2C1; and it should be remembered that we always have it in our power to convert one of these salts into the other by adding

excess of the acid which we wish to retain, since the other, becoming decomposed into gaseous constituents, may be entirely removed by warming the solution.

The nitric acid usually called "fuming" is generally red from the presence of N2O,, one of the products of its decomposition: its specific gravity is 1·536; and it solidifies at -49° C. to a very dark red mass.

All nitrates are soluble in water; and therefore this radical cannot be recognized by the formation of any insoluble salts.

It may, however, be identified by other processes :—

a. By setting free the hydrogen compound (nitric acid) by the addition of concentrated sulphuric acid to a nitrate, and subjecting it to the immediate action of copper turnings, which must be added simultaneously with the sulphuric acid, decomposition of the nitric acid ensues, with disengagement of nitric oxide gas (N,O,). The latter is recognized by being itself colourless but capable of acquiring a peculiar brownish red colour by mixture with air; it absorbs the atmospheric oxygen, and is converted into nitrous and hyponitric anhydrides (NO, and N ̧0).

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B. When nitric acid is produced from a nitrate by the action of concentrated sulphuric acid, the mixture cooled by immersion of the test-tube containing it in cold water, a crystal of ferrous sulphate added, and the whole allowed to rest, a dark halo is observed to form around the crystal, which, upon the application of heat, disappears with a kind of effervescence. This is due to the formation of a very singular combination of ferrous sulphate and nitric oxide having the formula 4Fe, SO, N2O2: heat decomposes this combination. The cause of its production is the decomposition of a portion of the nitric acid consequent upon the passage of the ferrous into the ferric salt, thus—

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10Fe, SO1+4H, SO ̧+2KNO ̧=3(Fe),(SO ̧),+K, SO
+4Fe2 SO1, N2O2+4H ̧0.

2 2

brown compound.

7. The nitrates do not reduce gold or mercurous salts; but when mixed with hydrochloric acid, they acquire the power of dissolving gold leaf.

d. Upon adding to a nitrate sulphuric acid and sulphindigotic acid, the colour of the latter is destroyed.

Of the acid-radicals containing phosphorus combined with oxygen, those existing in the phosphites and phosphates are of great analytical importance. The hypophosphites are rare.

means.

SALTS OF THE HYPOPHOSPHOROUS RADICAL, OR HYPOPHOSPHITES.

This acid-radical is of rare occurrence, being only produced by artificial It is obtained in the decomposition of phosphide of barium by water, or by boiling phosphorus with an alcoholic solution of hydrate of potassium, or with the aqueous solutions of hydrate of barium or calcium, until it disappears, and the vapour has no longer the odour of phosphuretted hydrogen. The phosphuretted hydrogen evolved during the process frequently causes dangerous explosions, which may be moderated by employing only a gentle heat. The barium or calcium salts thus obtained (BaH, PO2 or CaH, PO2) are very crystallizable.

THE HYDROGEN SALT (H, PO2), or hypophosphorous acid, is a viscid, uncrystallizable, very acid liquid, which when heated decomposes into phosphuretted hydrogen and phosphoric acid, thus-2H, PO=Н ̧P+H ̧PO̟. Although hypophosphorous acid is thus tribasic, one series of salts only is known, namely, the series of acid salts represented by the general formula MH, PO; they generally occur with water of crystallization, and are all soluble in water, and many of them also in alcohol.

This radical may nevertheless be recognized by several processes of decomposition:

a. When any dry hypophosphite is rather gently heated in a test-tube, decomposition of its radical occurs; phosphuretted hydrogen is evolved, which may be recognized by its odour and ready inflammability; and a pyrophosphate of the metal remains behind. The lead salt exhibits this decomposition best:

B. When mixed with an acid, hypophosphites reduce silver and gold salts, precipitating silver and gold; they also reduce mercuric and cupric salts. The same reactions take place more slowly with concentrated solutions of hypophosphites.

y. When boiled with excess of hydrate of potassium, alkaline hypophosphites evolve pure hydrogen gas:

KH, PO2+2KHO=K, PO1+4H.