260

CARBURET OF NITROGEN OR CYANOGEN.

CHAP. XI.

SECTION VII.

Carburet of Nitrogen, or Cyanogen.

To obtain cyanogen, it is necessary first to prepare a pure prussiate of mercury, by boiling fine powdered red oxide of mercury with twice its weight of prussian blue and a sufficient quantity of water. The compound is perfectly neutral, and crystalizes in long four-sided prisms truncated obliquely. It still, however, contains a little iron, which may be separated by digesting the liquor, before evaporation, with a little more of the oxide of mercury, and saturating the excess of this oxide with a little prussic acid (see vol. ii.), or even with a little muriatic acid. The prussiate of mercury, thus obtained, must be completely dried at a temperature below that of boiling water, and then exposed to heat in a small retort, or in a tube closed at one extremity. It first blackens, then liquifies, and the cyanogen comes over in the form of a gas, which may be collected over mercury. In the retort there remains a charry matter of the colour of soot, and as light as lamp black*.

1. Cyanogen is a true gas, or permanently elastic fluid. Its smell is strong and penetrating. It burns with a bluish flame mixed with purple. Its specific gravity is to that of common air as 1.8064 to 1. Hence 100 cubic inches at 60° Fahr. weigh 55 grains.

2. Water at the temperature of 60° Fahr. absorbs almost 41⁄2 times its volume, and pure alcohol 23 times its volume.

3. When 100 measures of cyanogen are detonated, in a Volta's eudiometer, with 250 measures of oxygen gas, 200 measures of carbonic acid result; and 100 measures of nitrogen. There remain, also, 59 measures of oxygen gas uncondensed. From these data, it is calculated by Gay Lussac, that cyanogen is composed of two volumes of the vapour of charcoal and one volume of nitrogen, condensed into a single volume. Its density ought, therefore, to be 1.8011, a number not very remote from that obtained by experiment.

4. Analysis by more complicated methods afforded the same result, evincing that cyanogen yields by a decomposition effected by means of oxygen, twice its volume of carbonic acid and an equal volume of nitrogen. No water whatsoever is formed during its combustion, if the gas be perfectly free from prussic acid vapour, a sufficient proof of the absence of hydrogen from its composition.

5. The solutions of pure alkalies and alkaline earths absorb cyanogen; and the liquid obtained, when poured into a solution of black oxide of iron, affords prussian blue, but not without the addition of an acid. At the same time, carbonic acid gas escapes in volume equivalent to the cyanogen absorbed, and there is a perceptible smell of prussic acid. These changes will be more evident from the following recapitulation:

* Gay Lussac, Ann. de Chim. vol. xcv.; or Thomson's Annals, viii. 37.

One volume of charcoal, uniting with one volume of oxygen, forms one volume of carbonic acid; the remaining volume of charcoal, uniting with half a volume of nitrogen and half a volume of hydrogen, composes prussic acid; and the residuary half volume of nitrogen and 1 volume of hydrogen compose together one volume of ammonia. 6. It will afterwards be shown, that when to two volumes of charcoal and one volume of nitrogen, together constituting cyanogen, one volume of hydrogen is joined, and the whole condensed into two volumes, we obtain prussic acid. Cyanogen agrees then with chlorine and iodine, in being acidifiable by union with hydrogen. Hence its compounds with metallic bases have been called by Gay Lussac cyanures, as those of chlorine are called chlorures; but having elsewhere expressed a preference for the name of chlorides, I shall, from analogy, give to the compounds of cyanogen the name of cyanides.

CHAPTER XII.

SULPHUR.-SULPHURIC ACID. SULPHATES.-BINARY COMPOUNDS OF

SULPHUR.

In describing sulphur and its compounds, I shall take them in the following order:

I. SULPHUR in its uncombined state.

II. Sulphur united with its full proportion of oxygen, constituting SULPHURIC ACID; and the compounds of this acid with alkalies and earths, termed SULPHATES.

III. Sulphur united with a less proportion of oxygen, composing SULPHUROUS ACID; and the compounds of this acid, called SULPHITES. It appears, also, from recent experiments, that there is a third acid, constituted of sulphur with a still less proportion of oxygen. This acid is at present known only in combination. It is called HYPO

SULPHUROUS or PER-SULPHUROUS ACID.

IV. The compounds of sulphur with alkalies and earths, termed

SUPLHURETS.

V. The combination of sulphur and hydrogen, named SULPHURETED HYDROGEN; and the compounds, which it forms with alkaline and earthy bases, called HYDRO-SULPHURETS.

VI. The compound of sulphureted hydrogen with a still farther quantity of sulphur, composing SUPER-SULPHURETED HYDROGEN; and its compounds with different bases called HYDROGURETED SULPHURETS, or sometimes SULPHURETED-HYDRO-SULPHURETS.

SECTION I.

SULPHUR.

I. THE sulphur, which occurs as an article of commerce, is a mineral production, and is brought to this country chiefly from Sicily.

That which is procured in our own island, is generally of very inferior quality, and contains a portion of the metal, from combination with which it has been separated. It is met with under two different forms; of a compact solid, which has generally the shape of long rolls or sticks; and of a light powder called flowers of sulphur. In general, the latter may be considered as most pure; but the two varieties, it will presently appear, are readily convertible into each other by the modified application of heat. Its specific gravity is 1.98

or 1.99.

II. Sulphur is readily fused and volatilized. When heated to 170° of Fahrenheit, it begins to evaporate, and to produce a very disagreeable smell; at 185° or 190° it begins to melt; and at 220° is completely fluid. If the heat be rapidly increased, it loses at 350° its fluidity, and becomes firm, and of a deeper colour. It regains its fluidity, if we reduce the temperature; and this may be repeated at pleasure, in close glass vessels, if the changes of heat be not slow; otherwise it is volatilized. It sublimes at 600o,

III. If, after being melted, it be suffered to cool, it congeals' in a crystalline form, but so confusedly, that we cannot define the shape of the crystals, farther than that they are slender interlaced fibres. If a large mass be kept fluid below, while it congeals at the surface, the crystallization there is much more distinct. When sulphur in complete fusion, viz. at 300°, is poured into water, it becomes tenacious like wax, and may be applied (as is done by Mr. Tassie) to take impressions from engraved stones, &c. These impressions are quite hard, when the sulphur has become cold. It is then of a red colour, and of the specific gravity 2.325.

IV. At the temperature of about 290° Fahrenheit, sulphur is converted into vapour; and if this operation be conducted in close vessels, the volatilized sulphur is again collected in a solid form. What remains has been called sulphur vivum. This affords an example of the process of sublimation, which differs from distillation, in affording a solid product, while the latter yields a condensed liquid. In this mode, sulphur may, in part, be purified; and its purification is completed, by boiling it repeatedly in distilled water; then in twice or thrice its weight of nitro-muriatic acid, diluted with one part of distilled water; and, finally, by washing it with distilled water, till this comes off tasteless, and incapable of changing the blue colours of vegetables.

be

V. When flowers of sulphur are digested in alcohol, no union takes place; but if the two bodies be brought into contact, when both are in a state of vapour, they enter into chemical union. This may shown by an ingenious experiment of La Grange, the apparatus for performing which is represented in the first plate of his "Manual." Into a glass alembic (see the plates to this work, fig. 2) put a little sulphur; over this suspend a small bot le filled with alcohol; and apply a receiver to the pipe of the alembic, the head being put into its place. Lute the junctures, and apply a gentle heat to the alembic. The sulphur will now be raised in vapour; and the vapour surrounding the bottle of alcohol, the latter will be volatilized, and will meet in this state the fumes of sulphur. A combination will take place

between the two bodies, and sulphurized alcohol will pass into the receiver. On pouring this preparation into water, the sulphur will be precipitated.

VI. Though it had already been suspected (chiefly from the experiments of M. Berthollet, jun. described in sect. 6, art. 4, of this chapter) that sulphur contains hydrogen, yet the first unequivocal evidence of the fact was furnished by Sir H. Davy. A bent glass tube, having a platinum wire hermetically sealed into its upper extremity, was filled with sulphur. The sulphur was melted by heat; and a proper connection being made with the Voltaic apparatus of 500 double plates, each six inches square and highly charged, a most intense action took place. A very brilliant light was emitted; the sulphur soon entered into ebullition; elastic matter was evolved in great quantities; and the sulphur, from being of a pure yellow, became of a dark reddish brown tint. The gas was found to be sulphureted hydrogen, or hydrogen gas holding sulphur in solution; and its quantity, in about two hours, was more than five times the volume of the sulphur employed.

Another proof of the presence of hydrogen in sulphur is derived from the action of potassium; for these two bodies combine with great energy, and evolve sulphureted hydrogen, with intense heat and light.

Lastly, when dry sulphur is burned in dry oxygen gas, Sir H. Davy is of opinion that, besides sulphuric acid, a portion of water is also formed; but he is still doubtful whether the hydrogen in sulphur can be considered as any thing more than an accidental ingredient. This view of the subject is embraced, also, by Berzelius*, who found, by heating sulphur with oxide of lead, that the quantity of water produced is much too minute to indicate any definite proportion of hydrogen in sulphur.

Another ingredient of sulphur, it appeared probable from the experiments of Sir H. Davy, is oxygen. For potassium, after being made to act on sulphureted hydrogen gas, evolved less hydrogen from water, than it ought to have done. It has since, however, been proved by Gay Lussact, that when all sources of fallacy are avoided, a given weight of potassium, which has been exposed to sulphureted hydrogen, separates exactly the same volume of hydrogen gas fi om water, as an equal weight of recent metal. Potassium, therefore, acquires no oxygen from the sulphur, which is contained in sulphureted hydrogen.

VII. Sulphur is inflammable, and appears susceptible of two distinct combustions, which take place at different temperaturest. At 140° or 150° Fahrenheit, it begins sensibly to attract oxygen; and if the temperature be raised to 180° or 190°, the combination becomes pretty rapid, accompanied by a faint blue light. But the heat evolved is scarcely sensible; at least it is so weak, that the sulphur may

*79 Ann. de Chim. 119.

† Ann. de Chim. vol. lxxiii. For an account of the oxides of sulphur, see Dr. Thomson's paper in Ni cholson's Journal, vi. 101.

thus be burned out of gunpowder, and the powder be rendered useless without inflaming it. At a temperature of 300°, its combustion, though still feeble compared with that of some other bodies, is much more active, and accompanied with a redder light. When set on fire in oxygen gas, it burns with a very beautiful and brilliant light; but of a given quantity of oxygen gas, it is not possible to condense the whole by this combustion, for reasons which hereafter will be stated. The product of these combustions, when examined, will be found to be sulphurous and sulphuric acid, but chiefly the former, and if water be carefully excluded, sulphurous acid only is formed. It is necessary, therefore, in order to produce sulphuric acid to make the experiment over water.

SECTION II.

Sulphuric Acid.

The properties of this acid must be exhibited by a portion of that usually found in the shops. They are as follows:

(a) Sulphuric acid has a thick and oily consistence; as may be seen by pouring it from one vessel into another.

(b) In a pure state, it is perfectly limpid and colourless.

83

When mixed suddenly with water, considerable heat is produced. Four parts, by weight, of concentrated sulphuric acid, and one of water, when mixed together, each at the temperature of 50° Fahrenheit, have their temperature raised to 300°.

When an ounce of water has been suddenly mixed with three of sulphuric acid, and the mixture been suffered to cool to the temperature of the atmosphere, an additional half oz. of water raises it to 86°, a second to 96°, and a third to 104°*. The greatest elevation of temperature, Dr. Ure finds to be occasioned by the sudden mixture of 73 parts by weight of strong sulphuric acid with 27 of water. This rise of temperature takes place, because the affinity or capacity of the compound of sulphuric acid and water for caloric, is less than that of the acid and water separately. A diminution of bulk also ensues; that is, one measure of acid and one of water do not occupy the space of two measures, but about th less; and the greatest condensation results, when those proportions are used, which give the greatest increase of temperature. Owing to the heat produced by its admixture with water, the dilution for ordinary pur poses, should be conducted very gradually; and the acid should be added to the water by small portions at once, allowing each portion to cool before a fresh addition is made. On the principle of its attraction for water is to be explained, also, the rapid increase of weight which the acid requires when exposed to air. In one day, three parts of sulphuric acid, exposed to the atmosphere, are increas

* 1 Philips on the London Pharmac. p. 24.