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red powder. Like sulphur, it is insoluble in water, a bad conductor of heat, and a non-conductor of electricity, though it is not, like sulphur, rendered electric by friction.
But all the general properties of this substance connect it with sulphur, though it approaches more in its external characters to those substances, which, from their lustre and other characters, are termed metals. It combines with hydrogen, oxygen, chlorine, phosphorus, and doubtless with all the bodies with which sulphur combines, forming analogous compounds. Its combining weight was calculated by its distinguished discoverer at 39.63.
Now, what are the conclusions which we are to draw from the similarity of the characters of sulphur and selenium? Can we believe that a substance like the latter, found in such rarity, and manifestly exercising so slight an influence on the constitution of natural bodies, is a simple body, differing not only from sulphur, but from the great mass of substances which exist in the world, in its molecular constitution? It were hard to believe so, and it were far more reasonable to suppose that selenium is a mere chemical compound, like some of the gems and rarer substances which are found in nature, produced by chemical combinations of other matters existing. We cannot perhaps bring the consideration of final causes into investigations purely chemical ; but when we find any thing disproportioned, and out of harmony in nature, we are at least bound to consider whether the seeming want of fitness may not rest with our inferences. Now, how can we infer from the mere fact that we have been unable, by artificial means, to decompose this substance, that it is to be ranked amongst the primary or simple elements of matter ? But if we cannot believe selenium to be in this class, so neither can we believe that sulphur is, although greatly more extended in nature ; for the two substances are so entirely analogous, that what we believe of the constitution of the one, we must believe of the other.
This substance occurs in the metallic state, chiefly associated with gold, silver, and bismuth. It is of rare occur. rence. It has a silver-white colour, passing into leaden gray, with the lustre of a brilliant metal. It conducts electricity, , although imperfectly, and heat slowly. Its specific gravity is about 6.2. It is very brittle, and may be reduced to powder. It fuses at a temperature a little higher than the melting point of lead, and when cooled slowly, crystallizes, assuming the rhombohedral form, in which respect it is isomorphous with arsenic and antimony. At a red heat, it is volatilized. In the air it takes fire at a high temperature, and burns with a bright blue flame bordered with green, rising in gray-coloured pungent fumes. It combines with hydrogen, carbon, oxygen, chlorine, and other substances, and in its combinations presents a close analogy with sulphur, connecting it with arsenic and antimony. Its combining weight has been calculated at 64.25. Its formula has been assumed to be H8 C4 04, which indicates 4 times the corresponding elements of sulphur. Similar remarks apply to this substance as to selenium. We cannot without violence to analogy assume that a body so rare is a primary element of nature. It is, therefore, a compound body, and so likewise must sulphur be, which resembles tellurium in all its essential chemical characters.
The chain of connexion between sulphur, selenium, and tellurium, may be said to be unbroken. They present the closest relation in their own properties, in their affinities for other bodies, and in the properties of their corresponding compounds. They all form with 1 equivalent of hydrogen a class of bodies resembling one another, all gaseous, and distinguished by a strong odour. Combined with 3 equivalents of oxygen, they form powerful acids, whose salts, the sulphates, seleniates, and telluriates, correspond even to their crystalline form, and the same close relation is exhibited in their other corresponding compounds.
But further, we have seen that these bodies pass into oxygen, between which and sulphur there exists a parallelism of properties, with respect to range of affinities and modes of combination, which strongly indicates a common origin. If we shall believe that tellurium is not a simple body, we are almost compelled to the belief that oxygen is not a simple body.
Nor are the links of the chain broken at tellurium. This body passes by anatural gradation, into others, namely, arsenic and antimony, and the latter, through bismuth, into copper and some of the most perfect of the metals, as will be afterwards shewn. But before proceeding with the description of arsenic and antimony, it will be necessary to advert to a substance, phosphorus, to which they are all related in so far as a common origin produces such a relation, and which itself is directly connected with nitrogen. But we are compelled to break the continuity of the series in this manner, because we are here adopting a linear arrangement, which is rarely that which accords with the natural arrangement of bodies, whether in the mineral or organic kingdom.
Phosphorus, so named from pus light, and pidev to carry, from its property of shining in the dark, exists in the mineral kingdom, in plants, and largely in animals, from the urine and bones of which it may be readily obtained. It is a soft solid body, nearly of the consistency of wax. It is usually of a light amber colour and semi-transparent, but when entirely pure, it is nearly colourless. By fusion and slow cooling, as well as by precipitation from its solution in naphatha, it may be obtained in crystals. Its mean specific gravity is 1.748. It fuses at the temperature of 108° F, becoming, before fusion, perfectly limpid and colourless, and dilating in volume by .0314, and this liquid, like other very inflammable bodies, possesses a high refracting power. At 217° it begins to rise in vapour, and at 550° it boils, and is converted into a colourless vapour. When exposed to the air it undergoes a slow combustion, which is sensible even at the melting point of ice, and is at length consumed. When undergoing oxidation, it emits a white vapour, having a smell like garlick, and which is luminous in the dark. This slow combustion of phosphorus may be retarded or prevented by increased pressure, and by the presence, in minute quantity, of the vapour of oil of turpentine, and some other compounds into which carbon largely enters. In pure oxygen, we are informed by Dr Graham, the oxidation does not take place at so low a temperature by many degrees, as when the oxygen is diluted with nitrogen, hydrogen, or carbonic acid. When kindled in the air, it burns rapidly, emitting a splendid white light, and producing intense heat; and in oxygen gas its combustion is yet more rapid, and the light evolved more beautiful and vivid. Being
so readily inflammable, it is ignited by a slight degree of heat. A temperature a little beyond that of its point of fusion, 108° F., inflames it readily in the air; nay, friction and pressure between the fingers, suffice to set it on fire, on which account it is usually kept in water, and operated upon in the liquid, and when it is fused, the operation is in like manner performed in water. Further, it may be volatilized even in common air, by mixing with the air a portion of the vapour of oil of turpentine.
Phosphorus is not soluble in water, but, when kept in the liquid, it is gradually covered with a white pellicle, which renders it opaque. It is soluble in small quantity in alcohol, ether, and oils. When the solution in alchol or ether is mixed with water, the phosphorus rises to the surface, though heavier than the liquid, and takes fire. When the solution in oil is taken to a dark place at a temperature not under 60°, it shines brightly. Phosphorus, like chlorine, is sensible to light, and acted upon by the violet rays of the spectrum.
It enters into combination with hydrogen, carbon, oxygen, sulphur, and other bodies. Its combining weight is reckoned by most chemists to be 31, although others hold it, and perhaps with better reason, to be one-half.
Of the compounds of phosphorus, remarkable ones are formed by its union with oxygen. It unites with hydrogen, forming a substance which has a great analogy with the combination of sulphur with the same element. Under the name of phosphoretted hydrogen, indeed, it is probable that combinations with slightly different equivalents of hydrogen are formed, but be this as it may, these compounds have a strong resemblance to one another, as well as to sulphuretted hydrogen. Now, sulphur and phosphorus are seen by the table to be derived from a common root CO.
All analogy leads us to the conclusion, that phosphorus is intimately connected with nitrogen, which forms so great a