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hydrogen are themselves not derivable from some other form of matter, or that hydrogen should be regarded as forming itself a class distinct from other bodies. In its physical and general chemical characters, it is manifestly in the same class as the other bodies which we term simple, and if they can be shewn to be compound with respect to their molecular constitution, so we must believe hydrogen to be. All that is here contended for is, that, while we can suppose other bodies to be derived from hydrogen, we do not know the form of matter from which hydrogen itself may be derived.

Questions sometimes arise regarding the relations of hydrogen with other bodies. By many it is held to be a metal, and some even seek to find its place amongst particular metals. It is quite possible that hydrogen, if solidified under the necessary conditions, would present the characters of a metal ; but it is equally possible that oxygen, nitrogen, or any other body would do so. It is contended that hydrogen, in certain compounds, takes the place of a metal, and therefore is to be regarded as a metal; but hydrogen likewise takes the place of oxygen, sulphur, and other bodies, which are not held to be metallic ; and therefore we have no reason to class hydrogen with the metals, in preference to other bodies, with which it is equally associated.

II. CARBON.

Carbon, unlike to hydrogen, exists in the solid form, and is the most fixed of known bodies. It is found in nature in the crystalline state, forming the most beautiful and brilliant of the gems. The diamond is usually colourless and transparent, and it is found likewise of various colours, red, yellow, green, blue, and even black, but always preserving the shining lustre proper to itself. Its specific gravity is 3.520, and it is the hardest substance in nature. Its primary crystalline form is the octahedral, or two four-sided pyramids, of which the faces are equilateral triangles, applied base to base. It is a non-conductor of electricity. It strongly refracts light, which gave rise to the memorable conjecture of Newton, that it was inflammable. When exposed to the solar rays, it becomes, as it were, charged with light, which it gives off again in the dark. Acids and alkalies the most powerful, have no action upon it. In close vessels it resists the most intense heat without fusing ; but if it is exposed to a red heat in the open air, or is inflamed in oxygen gas, it is entirely consumed, combining with oxygen.

Carbon is likewise found in the mineral graphite, commonly termed plumbago, or black lead, which contains a quantity of iron ; and in the mineral anthracite, which is essentially carbon, but which contains always a portion of hydrogen in combination.

Charcoal consists likewise essentially of carbon, and the foreign matters mixed with it may be separated. Charcoal, as is well known, is most largely obtained from the smothered combustion of wood, but may be obtained from most animal and vegetable substances when ignited in close vessels. The theory of the action in all these processes is the same. Carbon, hydrogen, and oxygen, form the essential constituents of all organic matter. When, therefore, such matter is exposed to heat, the volatile gaseous elements are thrown off, while the carbon, which is fixed, remains; and the air of the atmosphere is excluded in the process, because its carbon would otherwise combine with oxygen, and escape.

Carbon, as obtained from charcoal and other vegetable products, and purified from foreign matters, is opaque, and insoluble in water. It now conducts electricity, whereas in its crystalline form it was a non-conductor. It is infusible by heat, and, when excluded from the oxygen of the air, resists the most intense temperature which can be produced by art. Nevertheless, when exposed to the action of a powerful voltaic battery, it is partly volatilized, the attractive force of aggregation being partially overcome ; and a piece of charcoal exposed to this action increases in lustre, and becomes almost as hard as the diamond.

Carbon is inflammable, producing great heat during combustion. When strongly heated in the open air, it ignites and burns slowly, but in oxygen gas it burns with surpassing intensity, throwing off brilliant sparks. When heated, and thrown on nitrate of potassa, it deflagrates with violence, and when it is exposed to a red heat, and nitric acid is dropped upon it, the acid is decomposed, and a shower of sparks is thrown off.

Carbon, in the state of charcoal, possesses the property of condensing within its pores, the air of the atmosphere, and other gases, at common temperatures, and of yielding them again when heated, and different gases are absorbed by it in different proportions. Thus, in the space of 24 hours, it has been found to imbibe 90 times its volume of ammoniacal gas, 65 times its volume of sulphurous acid, 40 times its volume of nitrous acid, 35 times its volume of carbonic

ces.

acid, 94 times its volume of oxygen gas, and 14 times its volume of hydrogen. It likewise absorbs moisture from the air. When newly made, and left for a day exposed, it has been found to increase in weight 12 per cent. and more, the greater part of which increase of weight is due to the moisture absorbed.

It has the property of attracting the odoriferous and colouring principles of many animal and vegetable substances. Hence it is employed for depriving solutions of their colour, for destroying the offensive taint and effluvia of dead animal matter, and for purifying many substan

From the strong affinity of carbon for oxygen at high temperatures, charcoal is largely employed for the de-oxidation of metallic oxides.

Carbon, on the high authority of Berzelius, has been computed to combine with other bodies in the proportion of 6.13, hydrogen being 1; but, from more recent analyses, its combining weight has been estimated at 6.04.

Carbon is found largely in the mineral kingdom in the state of carbonate, and otherwise, and it enters into the composition of all the products of organic bodies. Its combination with oxygen forms two well known substances, carbonic oxide and carbonic acid.

Carbonic oxide is, at all known temperatures, and under every degree of pressure, an aëriform fluid, colourless, without odour, and incapable of being respired. When received into the lungs, even largely diluted with air, it is very hurtful, and when breathed, it almost instantly produces insensibility. It does not support combustion, but is itself inflammable. When set on fire it burns gently, with feeble light, and a lambent blue flame, resembling that of sulphur.

Its density is the same as that of nitrogen, which it also resembles in its action upon other bodies. It differs from

nitrogen in being inflammable, and readily reducible to its elements.

There are strong reasons for believing carbonic oxide to be isomeric with nitrogen, with respect to the number and ratio of its elements. And further, it may be regarded as a secondary root of a great number of compounds, thus :

CO+O Carbonic acid.

CO + Cl. Chloro-carbonic acid. 2 CO + O Oxalic acid, &c.

Further, the same combination, CO, whether we regard it as forming nitrogen, or carbonic oxide, or an element not yet insulated, may be assumed to be a secondary root of a great number of bodies, thus :

.

Ammonium,
Sodium,
Calcium,
Iron,
Chromium,
Cobalt,
Zinc,
Arsenic,
Strontium,
Molybdenum,
Uranium,
Copper,
Tin,
Antimony,
Bismuth,
Silver,
Mercury,

Gold,
and so forth, as in the table.

CO + H+
CO+ H9
CO + H6
CO + H13
CO + H14
CO + H15
2 CO + H4
2 CO + Ho
3 CO + H
3 CO + H'
3 CO + H12
4 CO + H?
4 CO + H2
4 CO + H8
4 CO + H15
7 CO + H10
7 CO + H3
7 CO+H

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