V. FLUORINE.

It is doubted whether this substance has yet been obtained separately from other matter, although many attempts have been made to insulate it. M. Baudrimont, however, by transmitting fluoride of boron over binoxide of lead, obtained a gas which he conceived to be fluorine, and, by employing another process, he procured it mixed, as he supposed, with hydrofluoric and fluosilicic acids, and he describes it as a gas of a yellowish brown colour, kaving an odour resembling chlorine, capable of bleaching, and as not acting on glass; and two gentlemen, Messrs Knox, obtained similar results. Other chemists have not been able to verify the experiments: nevertheless, it is extremely probable that the characters given are really those of fluorine, which, in this case, would greatly resemble chlorine.

The combining weight of this substance has been estimated by Berzelius at 18.75, by others at 18.08. It combines with other bodies in a manner so similar to chlorine, that it is impossible to doubt the intimate relation of the two substances.

It combines with hydrogen, forming an acid similar to that which chlorine forms with the same element. Hydrofluoric acid is a colourless liquid at the temperature of 32° F., and retains the liquid state at the temperature of 59° or 60°, provided the external air is excluded, but in open vessels it is dissipated violently in dense fumes. When a drop of it falls in water, a hissing noise takes place, like that produced by immersing red hot iron in the same liquid. It possesses the characters of an acid in a high degree.

Of all substances it is the most corrosive of organic matter. When the minutest portion of it touches the skin, im

mediate disorganization takes place; and hence the extreme danger of experiments upon it in the uncombined state.

It dissolves silica, its fluorine combining with silicium, and its hydrogen with oxygen; so that there are here two affinities called into play, namely, that of fluorine for silicium, and fluo-silicic acid for the water to be generated. in like manner acts upon boracic acid, whose composition is similar to silicic acid, and on titanic, molybdic, and tungstic acids, whose composition, it is believed, also approaches to that of silica. It acts powerfully upon glass, the fluorine entering into combination with silicium.

Fluorine probably combines with all the true metals, its affinity being greatest for potassium and the other alkaligenous metals, and gradually lessening for the less oxidable ones. With calcium it is found combined in the natural state, forming the beautiful mineral fluor-spar.

The combination of fluorine with silicium forms a colourless transparent gas, having an odour similar to that of hydrochloric acid, which extinguishes flame and irritates painfully the respiratory organs. It has the characters of an acid in a high degree. It is absorbed by water, which it decomposes at the instant of contact, so that when mixed with the air of the atmosphere, it forms a white cloud.

Fluoboric acid, like the last, is a colourless gas, having a penetrating odour, similar to that of hydrochloric acid. It has the acid characters in a high degree. It acts upon water in the same manner as fluosilicic acid, and indicates the minutest quantity of moisture in the air by the white cloud which it forms. It does not act upon glass. These two compounds, then, are extremely similar, indicating a similarity in the nature of the bases, silicium and boron.

VI. CHLORINE.

Chlorine exists at common temperatures in the gaseous state. It is of a greenish-yellow colour, and has a suffocating odour. It is wholly irrespirable, producing, when received into the lungs, even in small quantity, painful spasms, and a dangerous irritation. It may be reduced to the liquid form by a pressure equal to about 4 atmospheres, or 60 lb. on the square inch. It then becomes a limpid fluid of a bright yellow colour, which has not been solidified.

Chlorine gas is absorbed by water, and, at a low temperature, combines with it in a definite proportion. Under certain conditions, it is acted upon by the solar light. If water be present, chlorine gas decomposes the water under the influence of this agent, combining with the hydrogen of the water, and forming hydrochloric acid. The change takes place quickly in sunshine, more slowly in diffused daylight, and not at all in the dark. Chlorine, in combining with certain bodies, produces an evolution of heat and light. All the metals combine with it, and most of them inflame in it, when exposed to heat, and several of them, when reduced to a minute state of division, take fire in it at ordinary temperatures, the chlorine combining with the metal. It has a very powerful attraction for hydrogen, and many of the phenomena to which its action gives rise are due to this affinity. It has the property of destroying the colour of animal and vegetable substances. The presence of water seems to be necessary to this action; the chlorine decomposing the water, and uniting with its hydrogen. Sulphur possesses in some degree this property, and some of its compounds strongly. Chlorine possesses the property of acting

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upon the putrid effluvia arising from animal and vegetable substances, and destroying their odour.

The combining weight of chlorine has been calculated at 35.47, though chemists are not agreed on the precise number. It combines with other bodies in the manner of oxygen and sulphur, forming chlorides, just as they form oxides and sulphurets. It exhibits many points of analogy with sulphur, both in its own actions and those of its compounds. The assumed composition of sulphur, as shewn in the table, is H2 CO, or CO+H2; the composition of chlorine is H7 C2 02, or 2 CO+H', so that both bodies may be supposed to be derived from the same secondary root CO = N.

Chlorine, like sulphur, combines with oxygen in various proportions. These compounds constitute a group in which the oxygen is connected with the chlorine by slight affinities, and from which it is readily separated. On this account they form substances of great explosive powers. The combination Cl + 0, instantly destroys vegetable colours in the manner of chlorine itself. And the same property is possessed, though in a fainter degree, by the compound of sulphur with oxygen, SO + 0.

Chlorine, it has been said, has a great affinity for hydrogen. Hydrochloric acid is at ordinary temperatures in the state of gas, but it becomes liquid under a pressure of 40 atmospheres, at a temperature of 50°. This gas is without colour, and has an acrid suffocating odour, producing spasms. It has intense affinity for water, and whenever it escapes into the air, it is absorbed by the watery vapour, and a dense white cloud appears. If a jar filled with it be opened under water, the absorption of it is immediate, and the water rushes into the vessel with violence. It is in this state of aqueous solution, that hydrochloric acid is chiefly employed, and has been long known under the name of

spirit of salt, and marine or muriatic acid. This solution emits copious white fumes on exposure to the air, freezes at 60°, and, boiling at 110°, gives off hydrochloric acid. Chlorine, like fluorine, combines with silicium, forming a volatile liquid, which, when exposed to the air, evaporates almost instantaneously in the form of a white vapour.

It likewise combines with boron, forming an acid. The compound is a colourless gas, having a strong peculiar odour. It is rapidly absorbed by water, and is then decomposed.

Chlorine combines with all the other substances with which oxygen and sulphur combine. Its affinity is greatest for the alkaligenous metals, and gradually diminishes for the less oxidisable. Its compounds are of the highest interest in chemical science, in the arts, and in the economy of nature.

The compound body cyanogen presents a close analogy with chlorine in its actions and modes of combination. Now cyanogen is resolvable into nitrogen and carbon C2 N. At common temperatures it exists in the state of gas, but at the temperature of 45°, and under a pressure of 3.6 atmospheres, it becomes a clear liquid, which resumes the gaseous form when the pressure is removed. The gas is colourless, and possesses a strong offensive odour. It extinguishes burning bodies, but is itself inflammable, burning with a purple flame. It supports a powerful heat without being decomposed. It is absorbed by water in large quantity, and then undergoes decomposition. Cyanogen does not, any more than chlorine, exhibit the properties of an acid, but its aqueous solution does, by the production of acids from the mutual decomposition of the cyanogen and water. It combines directly with substances deemed elementary, as oxygen, hydrogen, sulphur, and the metals, in the manner of chlorine. It combines with hydrogen, sulphur, chlorine, and the allied bodies. Hydrocyanic acid H+Cy is a colourless liquid, and is still liquid, when free