It is the well-known pungent gas evolved when a sulphur match is burned, and is employed in many purposes of arts and manufacture, especially for the purpose of bleaching or removing colour. But the chief interest of this gas is in connection with its employment in the manufacture of sulphuric acid, or oil of vitriol as it is termed, when brought into commerce in union with water as a hydrate.

[The sulphuric acid of English commerce is a compound of one equivalent real or anhydrous sulphuric acid, and one of water; in other words, it is a protohydrate of sulphuric acid. It is formed by bringing sulphurous acid and aqueous vapour in contact with the

red fumes generated by the admixture of binoxide of nitrogen with atmospheric air.

The process of sulphuric acid manufacture varies in certain respects of detail, but its outline is as follows:— A mixture of sulphur and nitre is burned in such a manner that the results of combustion (sulphurous acid, and binoxide of nitrogen) may be conveyed into a leaden chamber, the floor of which is covered with water. Into the same chamber also enters a steam-jet. After the operation of combustion has been a certain time prolonged, and the water in the chamber has taken up as much sulphuric acid as it will absorb, it is drained off, and a portion of the water evaporated in leaden vessels. The total amount of evaporation necessary, however, can only be effected by means of retorts of glass or platinum, the latter being at this time almost universally employed. The final result is oil of vitriol of

* These red fumes, as was shown in the lecture on Nitrogen, are a mixture in variable proportions of hyponitrous, nitrous, and nitric acids. Sulphurous acid, being a powerfully deoxidising agent, removes oxygen from these, and becoming sulphuric acid falls upon a surface of water provided on purpose, and is dissolved. Occasionally a white crystalline body results in the course of this operation-a compound of nitrous acid, sulphurous acid, and a definite quantity of water-which compound, on falling into a reservoir of water below, becomes decomposed into sulphuric acid, which remains behind, and binoxide of nitrogen, which ascends. This white crystalline compound is, however, by no means an universal concomitant of the production of oil of vitriol, only occurring when the quantity of aqueous vapours employed in the operation has been too small.

English commerce. In some parts of Germany another process of manufacture is followed. Protosulphate of iron being distilled in large retorts, oxide of iron remains, and sulphuric acid, combined with water in the ratio of two equivalents of the former to one equivalent of the latter, comes over. Of this composition is the Nordhausen sulphuric acid; and it may be known from ordinary English oil of vitriol by its property of fuming in the air. These fumes are pure, dry, or anhydrous sulphuric acid, which may be obtained and collected by submitting the Nordhausen acid to careful distillation. It is not a little curious that pure sulphuric acid is a remarkably volatile body, whereas the combination of one of acid to one of water (common oil of vitriol), is so comparatively fixed, that any additional increment of water may be readily distilled away from it, as indeed is done in the ordinary commercial method of preparing oil of vitriol.]

When carefully formed and free from water, sulphuric acid has the appearance of a snow-white fuming mass, and is only capable of preservation in this state by carefully excluding the access of air and moisture. When dissolved in water, this snow-like sulphuric acid becomes the liquid sulphuric acid, or well-known oil of vitriol of commerce, a substance of powerful and very remarkable qualities. So powerful is oil of vitriol, so numerous its relations, so extensive its range of combinations, that we must consider it to be the very foundation on which chemical manufactures are built up.

Next in importance and interest after the oxygen compounds of sulphur, comes sulphuretted hydrogen, or hydrosulphuric acid, a compound, as its name indicates, made up of sulphur and hydrogen: nor is it the only compound resulting from a union of the two elements, although the only one which I think necessary to advert to on the present occasion. Sulphuretted hydrogen is naturally formed during the process of organic putrefaction—a circumstance which is demonstrative of a fact I shall have to insist on hereafter, namely, the presence of sulphur as a constituent of animals and vegetables. Sulphuretted hydrogen may also be generated by the direct process of pouring hydrogen over sulphur at an elevated temperature. This is not, however, the most usual process adopted for its preparation, which consists in developing it from a mixture of water, oil of vitriol, and sulphuret of iron, as I shall do here.

DIAGRAMMATIC REFRESENTATION OF THIS DECOMPOSITION.

Sulphuretted hydrogen gas, although exceedingly unpleasant as to odour, is a valuable re-agent to the chemist, who uses it for the purpose of separating metals from their solutions. These applications of the substance are, however, collateral to the purpose of my lecture, which is to indicate the leading peculiarities of sulphur, I have caused a portion of sulphuretted hydrogen to be prepared with a view to subsequent operations. One more experiment demonstrative of a leading quality of sulphur. Sulphur combines with hydrogen, as we have seen, forming a gas of very remarkable odour and striking chemical characteristics. If I burn this gas with the free accession of atmospheric air, you will observe that no deposition takes place; the result in this case being sulphurous acid, the gas just now produced by burning sulphur in oxygen and water. If, however, I partly close the bottle containing the hydrogen compound of sulphur, just after combustion has set in, then you will observe a powder becomes deposited.

Now, this powder is sulphur; and the experiment demonstrates that, violent though be the combustion of sulphur in oxygen, yet the balance of combining power for oxygen, as between sulphur and hydrogen, is slightly in favour of the latter. Such, then, are a few of the more powerful manifestations of sulphur; and before discussing the curious conditions under which it is found in organic life, I purpose bringing before your notice the leading qualities of the substance phosphorus; which being done, we