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IX. SULPHUR.

Sulphur is a solid, brittle substance, of a greenish yellow colour, having little taste, and emitting a peculiar odour when rubbed. It is found abundantly in the mineral kingdom, and is the produce, in an especial degree, of volcanic countries. It is found massive or in crystals, forming a part of many mineral species. It is found especially combined with various metals, as iron, lead, copper, zinc it exists in all the great series of rock formations, and extends throughout the vegetable and animal kingdoms.

Sulphur is a slow conductor of heat, and a non-conductor of electricity, and, when rubbed, the negative or resinous electricity is excited. Its density is 1.98, being nearly twice that of water. Its combining weight is usually reckoned 16.12.

It melts at the temperature of 216° F.; it becomes, by further heat, as fluid as water, and of an amber colour, and, being then cast into moulds, it forms the roll sulphur of commerce; by a further increase of heat, it becomes so viscid, that the vessel in which it is contained may be inverted without its falling out; by a yet further increase of heat, it becomes again liquid, and if, in this state, it be poured into water, it forms a soft, ductile, transparent mass.

It is a very volatile body, rising in vapour before it is wholly fused. It continues to be driven off according to the heat applied, until at 550° or 600° it is rapidly volatilized. This action, termed sublimation, is usually employed to purify sulphur, which is obtained in the form of crystalline grains known in the arts as flowers of sulphur. When heated in the open air to about 300° F., it takes fire and burns with a faint blue flame, emitting suffocating fumes of sulphurous acid.

It is itself insoluble in water, though, when precipitated from solutions in which it is contained, it unites with a definite quantity of water, forming a white powder, familiarly termed milk of sulphur.

It combines with hydrogen, carbon, oxygen, and nitrogen ; with chlorine, and the bodies allied to it; with phosphorus, arsenic, and the bodies of the same class; with silicium, and all the metals; and it may be said with every substance with which oxygen combines. It may in general be substituted for oxygen in the compounds into which the latter enters, and, like oxygen, it forms a class of salts in which it holds the place of oxygen, as well in the acid as the base.

Of its compounds with oxygen, one is sulphurous acid. This substance, S O2, is the product of the combustion of sulphur in dry air, or oxygen. It is a gas at ordinary temperatures, but is readily rendered liquid by being passed through a tube, surrounded by a freezing mixture. It is not decomposed at a high temperature, but various bodies, as carbon, hydrogen, and the alkaligenous metals, which have a strong affinity for oxygen, decompose it at a red heat. It has feeble acid properties, and produces a class of salts, which considerably resemble the corresponding sulphates, but which are readily decomposed by acids. It acts on many vegetable colours, for which reason the fumes of sulphur are employed to blanch certain substances, as silk and straw.

It may be supposed to be derived from a root SO, which has not been insulated, and may itself be regarded as a secondary root of a series of compounds, thus:

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Hydrosulphuric acid (HS) exists at ordinary temperatures in the gaseous state, but under a pressure of 17 atmospheres, and at a temperature of 50° F., it is condensed into a very clear liquid, which re-assumes the gaseous form on the pressure being removed. It has a strong offensive odour. It is very injurious to animal life. The presence of only part in air was found by the experiments of Messrs Thenard and Dupuytren, to be instantly fatal to a little bird; 1000 part killed a middle-sized dog; and a horse died in an atmosphere which contained only part of its volume

of it.

It extinguishes the flame of burning bodies, but is itself inflammable, burning with a faint blue flame, the products being water, sulphurous acid, and sulphur. It is rapidly absorbed by water.

This substance manifests slight acid properties. It resembles water or protoxide of hydrogen in this, that it combines with another equivalent of sulphur, and forms a persulphuret HS2, which resembles in a striking manner the corresponding peroxide of hydrogen. M. Thenard, the discoverer of the latter substance, treats at length of these points of analogy. Both have blanching properties, and whiten the skin; both are acted upon in a similar manner by the same bodies. Thus, charcoal-powder, platinum, gold, peroxide of manganese, and the oxides of gold and silver, which effect the reduction of peroxide of hydrogen into water and oxygen, effect the reduction of persulphuret of hydrogen into sulphuretted hydrogen and sulphur.

We need not pursue further the analogies between sulphur and oxygen. They are so great that chemists very generally, in their arrangement of the simple bodies, associate them together as forming a class, but they have omitted to refer this similarity of properties to that which we may fairly

assume to be the cause-similarity of constitution. In the table I have supposed sulphur to be resolved into H2 CO= H* C2. Oxygen is assumed to be represented by H2 C, so that sulphur contains twice the elements of oxygen in precisely the same ratio. This similarity of constitution is in perfect harmony with the similarity of characters, and I cannot accordingly entertain a doubt that the formulæ represent truly the composition of both bodies.

Sir Humphry Davy, in some of his earlier experiments, was led to the conclusion that sulphur contained hydrogen. He found sulphuretted hydrogen to be disengaged, when he exposed sulphur to the action of platinum-points ignited by voltaic action. He found likewise, that, when an alloy of tellurium and potassium was acted upon by melted sulphur, telluretted and sulphuretted hydrogen were disengaged equal to at least 80 times the volume of the sulphur employed. He states, that he made many experiments of this kind with similar results, the sulphur having been sublimed in azote, and moisture excluded with the greatest care; and he remarks, that while, in the experiments with voltaic electricity, it might be supposed that the hydrogen which was evolved, being only in small quantity, was the consequence of accidental mixture, in the other experiment with the alloy, the quantity of hydrogen evolved was too great to allow of such an inference.

These important experiments seem to have remained unheeded by Davy himself, and all subsequent chemists have agreed to regard the result as a consequence of the impurity of the sulphur. It is more probable that a portion of the sulphur itself was decomposed.

If we admit the conclusion to which all analogy conducts us, that sulphur is a compound body, we are necessarily led to the conclusion, that oxygen is likewise compound.

X. SELENIUM.

Selenium is one of the rarer bodies which chemical research has added to the substances termed simple. It has been chiefly derived from iron-pyrites; but it has been found likewise directly combined with sulphur in certain volcanic products, and sparingly, in combination with some metals, as copper, lead, silver, cobalt, mercury. It was first procured by Berzelius, from a manufactory of sulphuric acid, in which impure sulphur was employed. It was found that, in the leaden chamber in which the sulphur was received after combustion, there remained a reddish-coloured matter, which, when heated by the blow-pipe, emitted a peculiar odour, similar to that of horse-radish. This led to an investigation of the deposite, in order to separate the substance to which this odour was owing, from the matters with which it was associated, and the result was the discovery of this new body.

Selenium, when exposed to a heat somewhat higher than that of boiling water, melts, and, on cooling, becomes solid. It is then, like sulphur, a brittle opaque substance, without taste or odour. It has a metallic lustre, and when broken, its fracture has the aspect of lead.

At the temperature of 212°, it is semi-fluid, and at a few degrees higher it is completely liquid. When in its semiliquid state and cooling, it is so ductile that it may be drawn into fine elastic threads, which exhibit the gray lustre of a metal by reflected light; but which are transparent, and of a red ruby colour by transmitted light. It boils at about 650° F, giving off yellow vapours. When sublimed in close vessels, it condenses into dark drops of a metallic lustre, which unite into larger globules. When sublimed in the open air, it condenses in the manner of sulphur, in a fine

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