atom of sulphur + 1 atom of oxygen, and its representative number will be 16+ 8, 24. Its properties will again come under review in speaking of the several hypo-sulphites.

Hypo-sulphuric Acid.

This acid was discovered by Welter and Gay Lussac.* Their process for forming it consists in passing a current of sulphurous acid through water, in which finely powdered peroxide of manganese is kept mechanically suspended. There is immediately produced a perfectly neutral solution, consisting of hypo-sulphate and common sulphate of manganese. When the solution is sufficiently concentrated, pure barytes is added to the previously heated liquor, and agitated along with it, taking care to employ an excess of the earth. All the oxide of manganese is thus separated; and, sulphate of barytes being insoluble, the filtered liquor contains only the hypo-sulphate of barytes, and also the redundant portion of that earth. The latter is to be separated by a stream of carbonic acid, and subsequent ebullition to expel any excess of carbonic acid. The hypo-sulphate is then to be crystallized, dissolved in water, and decomposed by just the quantity of sulphuric acid, which is required to precipitate the barytes. The filtered liquor is to be concentrated, by exposing it under the exhausted receiver of an air-pump, along with a vessel of sulphuric acid, till it has attained the density of 1.347. If continued to be exposed, it is resolved into sulphurous acid which exhales, and sulphuric acid which remains liquid.

Oxygen gas, atmospheric air, chlorine, concentrated nitric acid, and red sulphate of manganese, are all inert on it at common temperatures. Zinc is dissolved by it, and hydrogen gas is disengaged by the decomposition of water, and there remains in solution hypo-sulphuric acid combined with oxide of zinc. It completely saturates salifiable bases, and affords neutral and soluble compounds with barytes, strontites, lime, and protoxide of lead; whereas sulphuric acid yields insoluble compounds with all those bases. At common temperatures these salts are permanent, but, when heated, sulphurous acid

• Ann. de Chim. et de Phys. x. 312.

escapes, and they pass to the state of sulphates, which are still neutral.

Hypo-sulphuric acid has been inferred to be composed of 100 parts of sulphur + 125 oxygen, setting apart that which is in the water essential to its existence; or we may consider it as a compound of 100 parts of sulphurous acid + 125 of sulphuric. Hence we have the four following acids with base of sulphur:

Sulphur, Oxygen. Sulphur. Oxygen. 1. Hypo-sulphurous acid. 100 + 50 or 1 atom + 1 atom. 2. Sulphurous acid..... 100 + 100 or 1 atom + 2 atoms. 3. Sulphuric acid... ...... 100 + 150 or 1 atom + 3 atoms. 4. Hypo-sulphuric...... 100 + 125 or 2 atoms + 5 atoms,

ART. 2.-Sulphur with Chlorine.

Sulphur, when heated in contact with chlorine gas, or even when exposed to it at common temperatures, absorbs it, and forms a singular compound first described by Dr. Thomson,* and afterwards investigated by Berthollet, jun.† Ten grains absorb nearly 30 cubic inches of gas, which is nearly in the proportion of 16 (the weight of an atom of sulphur) to 36 (the weight of an atom of chlorine). It appears, indeed, to be a true chloride of sulphur.

This fluid is volatile below 200° Fahrenheit. Its colour is red by reflected light, but yellowish green by transmitted light. It emits fumes, which are peculiarly acrid, and which excite a copious flow of tears. Its specific gravity is 1.6. When agitated with about an equal volume of water, an active ebullition and great disengagement of heat take place; sulphur is deposited; and the residuary liquid contains muriatic and sulphurous, and a small quantity of sulphuric, acids. Hence the water is decomposed, and while its hydrogen unites with the chlorine, its oxygen combines with the greater part of the sulphur. Alcohol and ether are decomposed with appearances of still more intense action, and it disunites also the elements of ammonia.

Nicholson's Journal, 8vo. vol. vi.

† Mem. d'Arcueil, tom. i.

Mercury acts strongly upon this liquid; its surface is first tarnished, great heat is evolved, and a grey powder is formed, which is a mixture of sulphur and chloride of mercury.

It reddens vegetable blue colours; but not till, by its action on water or on hydrogen, muriatic acid has been produced. Some chemists have considered it as an acid, and have proposed to call it the chloro-sulphuric acid; but besides being deficient in the other qualities of acids, it does not, like them, unite with salifiable bases.

Sulphur with Iodine.

Sulphur and iodine unite at a gentle heat, and a black radiated compound is formed, resembling sulphuret of antimony. It is easily decomposed at a degree of heat a little above that at which it was produced, and iodine is detached from it in vapour. Its precise composition is unknown.

SECTION VII.

Of Selenium.

In the chambers for manufacturing sulphuric acid, from the sulphur which is procured at Fahlun in Sweden, a reddish mass is deposited, which is principally sulphur. This substance, in burning, gave out an odour, which induced Berzelius to suspect that it contained tellurium, but on a minute examination he discovered, instead of that metal, a body with entirely new properties, to which he has given the name of selenium. The process, by which it was extracted, is described in the 13th vol. of Annals of Philosophy, p. 403; but as the source of it is extremely rare, it will be sufficient to refer to Berzelius's description. For the same reason, I shall give only a short account of this substance, confining myself to such of its properties, as are important from their influence on the general doctrines of chemistry.

The colour of selenium varies a good deal. When rapidly

cooled, its surface has a dark brown hue, and its fracture the colour of lead. Its powder has a deep red colour, but it sticks together when pounded, and then assumes a grey colour and a smooth surface. It softens at 212° Fahr., and completely fuses at a few degrees higher. While cooling, it has a considerable degree of ductility, and may be kneaded between the fingers, and drawn out into fine threads, which have a strong metallic lustre, an imperfect degree of transparency; and are red by transmitted, but grey by reflected light. When slowly cooled, it assumes a granulated fracture, and is extremely like a piece of cobalt. At a temperature nearly equal to that of boiling mercury, selenium enters into ebullition; and condenses, either into opaque metallic drops, or, when a retort with a large neck is used, into flowers of a fine cinnabar colour. Its vapour has a deep yellow colour, more intense than that of chlorine, but not so deep as that of sulphur.

When heated before the blow-pipe, it tinges the flame of a fine azure blue, and exhales so strong a smell of horse-radish, that a fragment, not exceeding of a grain, is sufficient to fill the air of a large apartment.

Selenium and Oxygen.-Oxide of selenium is formed by heating selenium in a close phial with common air, which acquires a very strong smell of horse-radish. Water agitated with this air imbibes the odour of the gas, and reddens litmus feebly, but this appears to be owing to the production of a small quantity of selenic acid. Selenic oxide gas is very sparingly soluble in water, and does not impart any taste to it. It does not combine with liquid alkalis. Its precise composition is unknown; but it appears to belong to the same class of oxides as carbonic oxide.

Selenic Acid.-Selenium dissolves in nitric and nitro-muriatic acids, and when the solution is evaporated in a retort, so as to expel the excess of those acids, there remains a white saline mass, which sublimes on raising the temperature, and forms a vapour, the colour of which closely resembles that of chlorine. In the cold part of the apparatus, selenic acid condenses in very long four-sided needles. These crystals, when first taken out of the retort, have a dry aspect and a

peculiar lustre. Exposed to the air, they adhere to each other, and the lustre becomes dull, but they do not liquefy.

Selenic acid has a sour taste, and leaves a slightly burning sensation on the tongue. It is very soluble in cold water, and dissolves in almost every proportion in boiling water. A saturated solution crystallizes, when rapidly cooled, in small grains, and when slowly cooled in striated prisms. The crystals dissolve in great abundance in alcohol, and the solution, when distilled, yields a fluid having an ethereal smell.

Selenic acid unites with different bases, and forms a class of salts called Selenates or Seleniates, which will be described with their respective bases.

Selenic acid is easily reduced both in the moist and the dry way. When a plate of zinc or polished iron is introduced into a solution of selenic acid mixed with muriatic acid, selenium is precipitated in the form of red, or brown, or blackish flakes. It is revived, also, by sulphureted hydrogen and sulphurous acid gases.

From his investigation of selenic acid, Berzelius has inferred it to consist of

On the supposition that it is constituted of an atom of base + 2 atoms of oxygen, the equivalent number for selenium will be 41, and for selenic acid 57.

Selenium and Chlorine.-Selenium absorbs chlorine gas, and becomes hot and forms a brown liquid, which, by an additional quantity of chlorine, is converted into a white solid mass. This is stated by Berzelius to be a compound of muriatic and selenic acids, but it is probably composed of chloride of selenium and the latter acid. It has not yet been accurately separated into its component parts, for when heat is applied, both substances are sublimed.

The remaining compounds of selenium will be described hereafter in their proper places. At present, it is only necessary to observe farther, that while this body possesses some