Page images
PDF
EPUB

hydrogen, arsenuret of hydrogen, and antimonuret of hydrogen. Phosphoretted hydrogen and ammonia greatly resemble one another, and the compounds of arsenic and antimony are not less alike in themselves and their compounds. Arsenious acid sometimes replaces oxide of antimony in combination, without changing the form of the compound; and arsenic and antimony are found together continually in the native state.

The probable composition of the four bodies enumerated, is represented in the table thus :

[blocks in formation]

XV. BISMUTH.

This metal exists either native, or in combination with other substances, as oxygen, sulphur, tellurium, arsenic, iron. That which is used in the arts is chiefly derived from native bismuth.

It is a substance of a reddish white colour, and of considerable brilliancy. Its structure is highly lamellar, consisting of broad shining plates, adhering together. It is brittle when cold, but when warm may be hammered. Its specific gravity is 9.53, which, by hammering, may be increased to 9.88. It fuses at the temperature of 4970, and expands in cooling. It sublimes in close vessels at a red heat, and when heated to about the same temperature in the open air, it takes fire and burns with a faint blue flame, emitting copious fumes of oxide of bismuth. When heated to whiteness by the blow-pipe, and thrown upon a hard surface, it burns brilliantly, rolling about.

Its combining weight is reckoned 71.07. Its sulphuret, which exists in the natural state, has the same crystalline form as sulphuret of antimony. The characters of this metal plainly connect it with anti

forms one of the sequence of substances from nitrogen and sulphur. But it manifests a progressive approach from the frangible metals to the more perfect and ductile, and in many of its properties resembles copper. It therefore distinctly connects the substances we have been considering with the perfect metals.

We might now exhibit the series of the bodies termed simple, continued from bismuth up to the most beautiful and perfect of the metals. In this case a series would be seen to exist from sulphur up to gold, thus :

mony, so that

[blocks in formation]

And this class of bodies may be termed the sulphur group, the several members of it passing the one into the other. I shall not, however, adopt this order of arrangement, because this

group of bodies is connected with another, touching upon it at all points, and being more or less connected with it in characters. This other division of the simple bodies I shall call the Siliceous Group, whose type is silicium, which body is distinguished, in an eminent degree, by its infusibility and hardness. But intermediate as it were between the sulphur and siliceous groups, are a few bodies, sparingly diffused in nature, which may be said to connect them together, and not to be very distinctly referred to either. These bodies are chromium, molybdenum, uranium, tungsten, tantalum, vanadium.

XVI. CHROMIUM.

This substance, so named from xewna colour, on account of its remarkable tendency to form coloured compounds, was first derived from a beautiful red mineral, dichromate of oxide of lead, obtained in a mine in Siberia, and popularly known as the red lead-ore of Siberia. This ore was used as a paint, but it has now become scarce and costly. The metal has since been found in the chromate of iron, a mineral which is a compound of the oxides of chromium and iron, and which occurs abundantly in Europe and America.

Chromium may be obtained by exposing its oxide, mixed with charcoal, to the heat of a smith's forge, or more readily by forming the chloride of chromium into a paste with oil, and exposing it to a strong heat for an hour, in a covered crucible lined with charcoal. In the one case, the oxygen, and in the other, the chlorine, combines with carbon, leaving the chromium free.

Chromium thus obtained is in grains, and the heat required to fuse it is so great that it has not yet been melted into mass. It has a white colour, intermediate between that of tin and steel, with a shade of yellow. It has a specific gravity of 5.9. It is very brittle, and easily reducible to powder. It undergoes little change by being exposed to the air, or kept under water. It may be likewise obtained by a peculiar process in the form of a finely divided powder of a dark colour, which only acquires the metallic aspect by pressure. In this state it takes fire when heated in the air.

Its combining weight is estimated at 28.19. It unites with the following, amongst other bodies, thus,

1. Sesquioxide,
2. Chromic acid,
3. Sesquichloride,
4. Terchloride,
5. Sulphur,

08
Cr 03
Cr2 CIS
Cr C13
Cr S3

It mixes with iron in indefinite proportions, but forms with it one known compound, apparently definite, of a crystalline texture, of a colour whiter than platinum, frangible, and nearly as hard as the diamond.

It is evident that this substance, while it has certain relations with the sulphur group, is yet more closely connected with iron. Assuming the theory indicated by the table, its composition is H" CO, while that of iron is H1 CO.

« PreviousContinue »