=

On the supposition that nitrous oxide is constituted of ong atom of nitrogen and one of oxygen, this would make the weight of the atom of nitrogen 13.4; for as 33.8 to 59, so is 7.5 to 13.4. (ƒ) Iron wire burns in this gas with much the same appearance as in oxygen gas, but for a shorter period.

(g) Nitrous oxide is rapidly absorbed by water that has been previously boiled, about one thirtieth the original bulk of the gas remaining uncondensed. A quantity of gas, equal to considerably more than nine-tenths the bulk of the water, may be thus made to disappear. This property furnishes a good test of the purity of nitrous oxide; for the pure gas is almost entirely absorbed by boiled water, which has cooled without the access of air. The gas employed should exceed the water three or four times in bulk, in order to obtain a saturated solution.

(h) Water, that has been saturated with this gas, gives it out again, unchanged, when heated.

(i) The impregnated water does not change blue vegetable

colours.

(k) It has a distinctly sweet taste, and a faint but agreeable odour. () Nitrous oxide is not diminished by admixture with either oxygen or nitrous gas.

(m) A mixture of this gas with hydrogen gas detonates loudly, on applying a lighted taper, or passing an electric spark.

When the proportion of hydrogen is nearly equal to that of nitrous oxide, or as 39 to 40, nitrogen gas only remains after the explosion; but when the proportion of hydrogen is smaller, nitric acid is also generated. In general terms, it may be stated that one measure requires one measure of hydrogen gas, and leaves after combustion one measure of nitrogen. Nitrous oxide forms, also (as I have shown, Philosophical Transactions, 1809, page 444,) a combustible mixture with ammoniacal gas, 100 measures of the latter requiring for saturation 130 measures of nitrous oxide.

(n) Nitrous oxide is not absorbed by alkalies; but if it be brought into contact with them, when in a nascent state, or before it has assumed the form of gas, it then enters into combination with alkaline bases. Thus, when a mixture of sulphite of potash and pure potash is exposed to nitrous gas, the gas is disoxygenized by the sulphite, and changed into nitrous oxide, which unites with the alkali. We obtain, therefore, a mixture of sulphate of potash with a compound of nitrous oxide and alkali, the former of which may be separated by priority of crystallization. The latter is composed of about three parts of alkali, and one of nitrous oxide. It is soluble in water, has a caustic taste, of peculiar pungency; and converts vegetable blues to green. Powdered charcoal, mingled with

it, and inflamed, burns with bright scintillations. The nitrous oxide is expelled from fixed alkalies by all acids, even by the carbonic.

(0) Animals, when wholly confined in this gas, die speedily.

() One of the most extraordinary properties of this gas is exhibited by its action on the human body, when received into the lungs. When thus employed, it does not prove fatal, because, when received into the lungs, it is mixed and diluted with the atmospherical air present in that organ. To administer the gas, it may be introduced into an oiled silk bag or clean bladder, furnished with a stop-cock, and may be breathed repeatedly from the bag and back again, as long as it will last. The sensations that are produced vary greatly in persons of different constitutions; but, in general, they are highly pleasurable, and resemble those attendant on the pleasant period of intoxication. Great exhilaration, an irresistible propensity to laughter, a rapid flow of vivid ideas, and an unusual fitness for muscular exertion, are the ordinary feelings it produces. These pleasant sensations, it must be added, are not succeeded, like those accompanying the grosser elevation from fermented liquors, by any subsequent depression of nervous energy.

SECTION IV.

Nitrous Acid.

Ir has been a subject of controversy whether an acid, entitled to this denomination, and holding the same relation to the nitric, which the sulphurous bears to the sulphuric, has really existence. That the acid, obtained from nitre, has different states of oxygenation, and contains a less quantity of oxygen in proportion to the depth of its colour, is generally admitted. But it has been contended that we are to consider all these varieties as nitric acid, holding in combination variable proportions of nitrous gas; and the principal argument in favour of this theory is that the substance, occasioning the colour, may be separated by the mere application of heat. Sir H. Davy, in the year 1800, gave the following table, showing the proportion of nitrous gas in nitrous acid of different colours.

Mere dilution with water is sufficient to vary these colours. Thus the dark orange-coloured acid, by dilution, passes through the shades of blue, olive, and bright green. Nitric acid, also, by absorbing nitrous gas, has its specific gravity diminished. Colourless acid, for example, when rendered of pale yellow, becomes lighter in the proportion of 1.51 to 1.502.

It is now, however, generally admitted that the nitrous acid is as much a distinct and peculiar compound as any other of the compounds of nitrogen.

The proportions of its elements have been investigated by Sir H. Davy,* who finds that two measures of nitrous gas and one of oxygen, (= 1 volume of nitrogen and 2 of oxygen), both freed from moisture, and mixed together in a vessel previously exhausted of air, are condensed into half their volume,† and form a deep orange-coloured elastic fluid, which may be called nitrous acid gas. It has the following properties:

A taper burns in it with considerable brilliancy. Sulphur inflamed does not burn in it; but phosphorus burns vividly. Charcoal continues to burn in it with a dull red light. Water absorbs it and gains a tint of green. It reddens litmus paper, has a sour taste, a strong smell, and turns animal substances yellow. One hundred cubic inches, calculating from the condensation of its elements assumed by Davy, must weigh 65.3 grains, at mean temperature and pressure, and it must contain in 100 grains,

stp.

To form liquid nitrous acid, nothing more is necessary than to saturate water with this vapour. The water becomes first green, then blue, and finally an orange colour more or less deep. The latter may be brought to the state of green or blue by adding more or less water. Hence the colour depends merely on the circumstance of density.

With

The properties of liquid nitrous acid, Berzelius remarks, differ from those of nitric acid; for while the latter boils at 236°, nitrous acid of the same density boils at 160°. The purely acid part he considers to be composed of 36.9 nitrogen + 63.1 oxygen. bases, it forms a class of salts, which, he asserts, differ entirely from those containing nitric acid. On the other hand, we have the testimony of Gay Lussac that the nitrous acid is decomposed with so much facility by contact with alkaline solutions, as to be inca

* Elements of Chem. Philosophy.

bot Gay Lussac states the condensation at two thirds of the volume of the nixture. Ann. de Chim. et Phys. i. 403.

in

13 Ann. de Chim. 10.

pable of forming a distinct class of salts. With solution of potash, for example, he found that it affords pernitrate and nitrate, but nothing that can properly be called a nitrate of potash.*

SECTION V.

Of Per-nitrous Acid.

WHEN 400 measures of nitrous gas and 100 measures of oxygen (in which the nitrogen and oxygen are to each other by measure as 100 to 150) are mixed together over a solution of potash confined by mercury, we obtain 100 measures of a compound, called by Gay Lussac per-nitrous acid. Mr. Dalton, who obtained it several years ago, and then considered it as nitrous acid, has lately proposed to call it sub-nitrous acid; but the name suggested by Gay Lussac seems to me more conformable to analogy, since the new acid differs from nitrous acid in containing an additional proportion of nitrogen. This new compound is so far hypothetical, that it has never yet been exhibited in a separate form; for when a stronger acid is added, to expel it from the potash, it is resolved into nitrous gas and nitrous acid.

Per-nitrous acid is, also, frequently generated, when nitrous and oxygen gases, or nitrous gas and common air, are mingled together in eudiometrical processes. At the same time nitrous and nitric acids are produced in proportions to the per-nitrous and to each other, which are modified by the circumstances of the experiment.§

Calculating from the proportions of its elements and their state of condensation, 100 cubic inches of per-nitrous acid gas must weigh 80.2 grains; and it must consist in 100 grains of

Per-nitrous acid unites with sulphuric acid, either concentrated or a little diluted, and, at a moderate temperature, the compound forms elongated four-sided prisms. These crystals, and even the liquid in which they are formed, give nitrous gas when brought into contact with water. A similar solid is obtained by passing nitrous acid vapour into sulphuric acid; and it appears, also, to be identical with the crystalline solid formed by Clément and Desormes by the mixture of oxygen gas, sulphurous acid, nitrous gas,

* Ann. de Chim. et Phys. i. 409. Thomson's Annals, vol. ix.

† Ibid. i. 400.

Dalton, Thomson's Annals, x. 83.

and the vapour of water.

The last-mentioned compound had been supposed to consist of nitrous gas and sulphuric acid; but sufficient reasons have been given by Gay Lussac for the new view of it, which has just been stated.

SECTION VI.

Nitrates.

ART. 1.—Nitrate of Potash.

I. A DIRECT Synthetic proof of the composition of this salt may be obtained by saturating nitric acid with potash, either pure or in a carbonated state. The solution, on evaporation, yields crystals of nitrate of potash, or nitre.

For the purposes of experiment, however, the nitrate of potash, which may be met with in the shops, and which is an abundant product of nature, may be employed on account of its greater cheapness. The nitre, which is met with as an article of com. merce, is brought to this country, chiefly from the East Indies. When it arrives it is a very impure salt, containing, besides other substances, a considerable proportion of muriate of soda. In this state it is called rough nitre. For the purposes of chemistry, it requires to be purified by solution in water and re-crystallization; and it then obtains the name of refined nitre, or refined saltpetre. II. This salt has the following properties:

(a) It crystallizes in prismatic octahedrons, generally constituting six-sided prisms, terminated by two-sided summits. It contains, according to Berzelius, no water of crystallization. Thenard has determined that it consists of

49.5 potash

50.5 nitric acid.

But as potash itself, in the driest form under which we can procure it, still contains water, Berthollet has given the following proportions as those of nitrate of potash:

50.1 potash
49.9 acid

100.*

These proportions are nearly reversed by Berard, who makes it consist of 48.64 base and 51.36 acid.† The proportions, deduced by Dr. Wollaston, are 46.67 base to 53.33 acid: and those by Dr. Ure 47 base and 53 acid.

* Mem. d'Arcueil, iii. 170.

† 71 Ann. de Chim. 69.