cette combinaison se forme autorise à conclure en supposant le charbon contient encore de l'hydrogène que c'est néanmoins le soufre qui en donne la plus grande partie.” *

que

Sulphureous Acid. Fumes of Sulphur.-When sulphur is rubbed, it acquires a peculiar smell, but when heated nearly to the point of inflammation, very suffocating fumes ascend, and when it burns, they are generated in vast quantities. They are developed in volcanic regions, and where coal, containing pyritic matter, is consumed. They are very injurious to the lungs, and to the vegetable organization it has been ascertained, that a mixture in the air, so slight as not even to affect the senses, curls the leaves and injures the health of plants. Hence, one cause of the inferiority of vegetation in smoky districts, where coal is burned.

The same fumes are generated when sulphur is burned in vital air; and there can be no doubt that it is a case of simple combustion, in which every atom of the radiant matter of the vital air is replaced by a particle of sulphur. a particle of sulphur. The atomic weight of a particle (Fig. 47.) is 20, or half that assigned by Thomson or Dalton. It evidently possesses the structure which discharges colours already described, and this property it is found to possess, though, in consequence of its acid nature, it first reddens them. The particles of oxygen in the sulphureous gas may perhaps remain in the same positions as in vital air, with sulphureous, instead of radiant poles. In which case, 100 inches would, in their nascent state, weigh 31 + 30 grains; but sulphur is such a form, that, immediately on coming into the radiant medium, it can only be expected that every particle shall become charged with atoms to fill up and relieve the excessively negative-electrical state of its equator, the limit of which is six atoms to every binate molecule of the sulphureous gas. This would raise its weight from 60 to 70 grains. If, again, we suppose that the sulphur is arranged in quaternate molecules, or molecules of fusion, constituting aërial mole

• Memoires d'Arcueil, t. i. p. 331.

cules, which, like others of similar magnitude, occupy a double volume, the central particle of sulphur in every molecule will be free from atoms, its demand for matter in the hollows of its equator being satisfied by the three surrounding particles of sulphur. This will reduce the weight of 100 inches 2.2 grains, and it will therefore be 67.8 grains; and this will be about that quantity found by the balance, as its atomic refractive power is the same as that of common air. Sir H. Davy, Thomson, and Thenard, found it about 68 grains.

Molecules of this form are extremely impatient of the gaseous state. The fumes of phosphorus, whose structure we shall find in the highest degree analogous, cannot be prevented from aggregating in flocculi, which are precipitated, and those of sulphur can only be sustained in vessels composed of a substance for which they have no affinity, when no water is present, and when the medium is not intensely cold.

This gas may be reduced into a liquid state by being passed through a very cold tube, or by being pressed by two atmospheres. Water absorbs it very readily, and remains for some time a fuming liquor, from which the fumes may, for some time, be recovered in a free state. But when the access of more oxygen, or vital air, has been afforded, the water loses its sulphureous odour, becomes intensely sour, and may be raised to the temperature of 550° Fahr., without giving off any other vapour than pure steam.

Oil of Vitriol.-Sulphuric Acid.-The sulphur, water and oxygen have now arranged themselves in a form of great symmetry and stability. Two particles of sulphureous acid having inserted themselves in the two poles of a particle of water to which they are conformable, the two particles of oxygen, aided by a third derived from the atmosphere, have moved from the poles to the equator, and thus three particles of oxygen, the number demanded by a particle of water, are arranged on the alternate segments of its equator, while the particles of sulphur remain inserted, one in each pole, forming an axis to the molecule, as in Fig. 48.

The atomic weight of a particle of oil of vitriol in those cases where the sulphur still retains the radiant matter, is 68.

In cases where it is free from atoms, its weight is 62. Now, Sir H. Davy assigns the constitution of oil of vitriol to be 30 sulphur, 45 oxygen, and 17 water; and 30, 45, and 18 are in the same ratio as 20, 30, and 12, the proportions just assigned. Oil of vitriol is, at ordinary temperatures, a liquid, having the aspect as to fluidity of oil; but it differs remarkably in being very heavy, in possessing a very low refractive power, in mixing with water in all proportions, in dissolving and corroding the skin, and in charring vegetable substances. It boils between the melting point of tin and lead; and both stronger and weaker acids are reduced by boiling to the same degree. In this there is no water present except that implied in its constitution, and it corresponds to the hydronitric acid formerly described. It is frozen with extreme difficulty. But at that degree of dilution, when one particle of water is supplied to every particle of oil of vitriol, it is evident that it may very readily assume the spicular form, a series of particles being united by the concave poles of the particles of water between each, which serve as a connecting box. In consequence of this insertion of the poles of the sulphur into the poles of the water, condensation ensues during dilution, and there is a loss of the specific heat of these poles of the sulphur, and much heat is given out.

A binate hydrated molecule, consisting of one particle of oil of vitriol with one of water on each pole, is the most symmetrical and dense state in which the acid can exist, and, consequently, at this degree of dilution the condensation ought to be greatest, the ratio of acid to water being 62 or 65 to 24. Now, Dr Ure found the greatest condensation when the ratio

of oil of vitriol to water was 73 to 27, which are in the ratio of 65 to 24, or 62 to 23.

The conformable character of the particle of oil of vitriol to water, and its deficiency in quiescence of electrical state, are indicated by the avidity with which it unites to water, desiccating, in a remarkable manner, the atmosphere around it, and becoming weaker by absorbing the vapour. It decomposes vegetable substances, seeming, in many instances, to resolve them into water and charcoal; hence when straws, or other vege table bodies, fall into oil of vitriol, the liquid becomes brown and discoloured by the mechanical suspension of the disengaged charcoal. In some cases, it appears also that oil of vitriol is discoloured by the generation of a little selenium, as has been suggested by Dr Thomson, and since ascertained.

This powerful acid is a production of volcanic regions, existing both in a liquid state and that of vapour : it also occurs united to metallic oxides, constituting salts. For the purposes of chemistry and the arts, it is usually prepared by burning sulphur with nitre over water, or by expelling it from green vitriol, a salt of iron in which oil of vitriol exists abundantly. When this salt is distilled at a strong heat, a liquid of a dark colour and oily consistence comes over, which, unlike oil of vitriol, boils at a very low temperature, and gives off fumes at all temperatures. It consists of oil of vitriol and anhydrous sulphuric acid. The latter is a form in which the oxygen and sulphur are in the same proportion as in oil of vitriol, but in such a state of impatience to become oil of vitriol, that, when a little of it is dropt in water, it hisses like a red-hot iron. When this fuming liquor is distilled, the anhydrous acid comes over, and, by cooling successfully, it may be condensed into a solid white silky asbestiform body. It often happens, that oil of vitriol, when offered union with certain bodies, parts with its water, which is replaced by the base, and then its atomic weight is that of the anhydrous acid, 50 or 53, or, perhaps in some cases, even 56.*

The atomic weight of anhydrous sulphuric acid is generally stated at 30, and that of oil of vitriol at 61.25, and, disregarding the accidental

Hyposulphuric Acid.-Sulphureous acid and oil of vitriol are the substances which naturally result from the union of oxygen and sulphur. By the ingenuity of Welter and GayLussac, these two substances have also been made to unite with each other, so that the two naked poles of the oil of vitriol are covered by two particles of sulphureous acid. The beautiful form which results has obtained the name of Hyposulphuric Acid. It has a sour taste, reddens vegetable colours, and unites with bases forming soluble salts. The application of heat drives off the sulphureous acid and leaves oil of vitriol. Its atomic weight is 102, (sulphur 40, oxygen 50, water 12). The same ratio of sulphur and oxygen would, however, result, if a quaternate molecule of the former had a particle of oxygen on all its poles. This would be an anhydrous hyposulphuric acid, whose atomic weight would be 90, as commonly assigned.

The Hyposulphuric Acids.—Besides these there are probably three other acids of sulphur that have been prepared in the laboratory. Two of these possess very simple structures, and have both been described under the name of hyposulphureous acids.

There are two forms in

1. Hyposulphureous Acid of M. Gay-Lussac and Mr Herschel. By deoxidizing every other particle in a quantity of sulphureous acid, or by supplying every one with an additional particle of sulphur, an acid results in which the ratio of sulphur and oxygen is 2 to 1. which this ratio is compatible with a symmetrical existence. The particle of oxygen may have one of sulphur in each pole, or a quaternate molecule of sulphur may have one of oxygen on each pole of the central axis. In the former case its atomic weight is 30, in the latter 60. The progress of development appears to be, that the former changes into the latter,

atoms to which both are incident, 50 and 62 are the true weights; but it will only be by subsequent experiments that we shall learn how far we can count upon an uniform atomic weight.