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of water, on iron filings, or granulated zinc, and the gas so procured possesses the following properties.

(a) It is inflammable in atmospheric air or oxygen gas; that is, it enters into electro-chemical union with a body possessing opposite electric qualities, or in other words hydrogen being, as it is termed. pontive to oxygen, which latter is negative to hydrogen, the two gases tend to form an union either from the attractive influences of their two electricities, or, it may be from their peculiar electrical condition.

(b) It will not burn unless it be in contact with one or other of those substances which are termed supporters of combustion: thus an ignited jet of hydrogen gas will be instantly extinguished if plunged into a vessel containing the same gas, provided it be absolutely pure, and free from the slightest admixture of common air or oxygen gas.

(c) It has an unpleasant smell, at least when it has been procured by the agency of metals in the decomposition of water.

We may collect, from all that has been advanced, that hydrogen gas is considered by chemists, as an elastic fluid, consisting of a peculiar base, in combination with a large portion of caloric, or the matter of heat; but which calorie is latent, (that is, in a state wherein it makes no sensible addition to the heat of the body with which it is combined); that its peculiar levity is owing to its capacity for caloric, which "separates the particles, and gives the whole a gaseous form," causing these particles to repel one another by the power of repulsion, which is known to exist in the particles of caloric among themselves.

99. The base of hydrogen gas has never been detected in a separate state; nor does it appear that chemists have in any instance, been able to determine what its nature really is. Some have supposed, that it may be a metal, and I am inclined to believe that Sir Humphry Davy once expressed an opinion to that effect. Be this as it may, hydrogen gas, as has been seen in Dr. Birkbeck's experiment, 85, separates at the negative pole; and from having observed that alkalies attached themselves to the same pole, Sir Humphry Davy was led to perform those experiments which terminated in the discovery of the metallic nature of potass, soda, and other alkaline substances. To me, hydrogen gas appears to be a peculiar base in electro-chemical union, with a very large proportion of electricity of a specific kind, and which might be distinctively styled the electricity of hydrogen. This gas, as has been observed, can be procured in a pure state, solely from water; and its base has never been detected in a separate state: hence, I would suggest, that it exists, and is ofllytboe found in water; which fluid may then be philosophically considered as the primeval, and sole natural source of hydrogen throughout the creation, be its subsequent combinations as numerous and multiform as they may. If water, then, be the grand and only source of hydrogen, as a base, it may be admitted that, the first sunbeam, by its electrizing influence, developed the first atom of hydrogen gas, both within, and above the surface of the earth,—in a state of simple purity, as well as in all the varieties of those combinations, that may be termed oxides of hydrogen: among which, atmospheric air may probably be considered as by far the most important. I do not assert that hydrogen gas cannot have a metallic base; but I think it much more probable,—taking into consideration, the universal diffusion of water, and the peculiar metallic composition of meteoric stones,—that the metals owe their origin to hydrogen, than that the base of hydrogen is to be sought for in metals. This conjecture will acquire probability from the circumstance that potass, and other alkaline substances are detected in the ashes of several plants; and indeed, we may be led to ask, from what portion of the vegetable substance, can the process of burning form and develope the bases of those metallic oxides that we term alkalies, unless it be from the hydrogen which it contains? The inquiry is one of a peculiar interest, and well worthy of the attention of the philosophic chemist.

100. The decomposition of ammoniacal gas tends to confirm the theory of the electrization of hydrogen. That gas is found by analysis to consist of three definite proportions of hydrogen gas, and one of the gas termed azote, or nitrogen. If a cubic inch of ammoniacal gas be conveyed into the detonating tube, (fig. 2, No. 96,) standing over mercury, and a succession of from 150 to 200 electric shocks be passed through it, the volume of gas will be much enlarged by the disturbance of the chemical union of the two constituents. It will be found also, that the quality, as well as the volume of the gas, has undergone a change, for it is no longer absorbable by water; whereas, ammoniacal gas is so, to a very great extent. Under these circumstances, if about one-third of the bulk of very pure oxygen gas be admitted, and another electric shock be passed through the wires, a loud detonation will ensue, the volume will be reduced, traces of water will be perceived, and the remaining gas will be found to consist chiefly of azote. Electric agency has effected these changes; and thus we have decisive evidence, that the chemical phenomena of decomposition, and the formation of a new compound, have been induced, and effected by that agency. If this be admitted, it must follow as a necessary consequence, that all chemical action depends chiefly, if not altogether, upon electric agency.

101. Of the nature of oxygen.—Oxygen, according to Parkea, "is the basis of vital air, as well as one of the constituent parts of water; it is the chief support of life and heat: and performs an important part in most of the changes which take place in the mineral, vegetable, and animal kingdoms."—(End. 114.)

"We have given," says Lavoisier, "to the base of the respirable portion of atmospheric air, the name of oxygen, from o%vs, acidum, and yeivofiai, gignor, because one of the most general properties of this base is to form acids, by combining with many different substances. The union of this base with caloric, which is the same with what was formerly named pure, or vital, or highly respirable air, we now call oxygen gas.

Mr. Hume, of Long-acre, printed a little pamphlet, from a paper which had been addressed by him to Mr. Tilloch, in July 1808, and which appeared in the Philosophical Magazine, vol. xxx. Its subject was, "The Identity of Silex and Oxygen:" this pamphlet is now before me, and from it I shall extract some passages, which may tend to excite much interest and reflection. I have been obliged somewhat to abbreviate, but the extracts are absolutely faithful; and whenever the phraseology is altered, the meaning remains unchanged. At pages 5, 6, and 7, Mr. Hume says, "All organized bodies either contain silex, or, what I shall consider as a modification, oxygen. In a geological view of this subject, where can we turn our eyes, or employ our thoughts, without meeting this grand and multifarious cement,—this bond of aggregation, that fixes the solidity of all tangible nature? The very outlines of our planet are traced out with it; and all primitive matter, from the most stupendous mountain, or rugged precipice, to the deepest cavern, even to the centre of gravitation, we are warranted to say, is replete with silex.

"Where, then, ought silex to be placed, in the arrangement of simple elements? Were I asked for an answer to such a question, I would say, that seeing nothing to which it has the slightest resemblance in its effects, but oxygen gas, of which I conceive it to be the true base, here I would not only assign its proper rank, but give it also a precedence to all other elementary matters that had resisted decomposition. It is hardly necessary for me now to add, that I do not consider oxygen in the state of gas, to be a simple body; for whatever is susceptible of spontaneous change, should always be deemed a compound of at least two elementary substances." Mr. Hume then alludes to the liability of oxygen gas to undergo this spontaneous change, on the authority of Messrs. Allen and Pepys, who found that it "will happen, though the gas be of the purest kind,—that obtained from oxy-muriate of potash,—and even when secured in glass vessels with glass-stoppers."

Having assumed silex and the base of oxygen gas to be synonymous, and simple bodies, Mr. Hume defines what he means by the word silex,—namely, "the very pure part of rock-crystal, and that which constitutes by far the greatest portion of all sand, flint, gravel, and other well-described rocks, stones, and minerals: a substance common in every spot of the globe, in every zone, and in every climate; and an article so obvious and familiar to the meanest capacity, that any further description would be superfluous. In rockcrystal—in quartz, and in hot springs, silex is nearly in its pure and primitive state of perfection."

In his researches for oxygen, Mr. Hume, (pages 7 and 8,) says, "Let us consider this our sublunary world under its three grand divisions. The first is the atmosphere,—the aeriform division of nature. Here, it is allowed, the principal element is oxygen; but it is now in the gaseous state; that is, it is saturated with caloric. I have said the principal element, because it is the most important of all others: it is the matrix of fire; it is the pabulum of life; in short, such is its consequence and value to the very being of all organized matters, whether in the animal, vegetable, or mineral kingdom, that surely some more appropriate name might have been devised, than that which it now bears." Mr. Hume adds, that by modifying, or in some measure reversing the phlogistic theory, both the theory, "and the word phlogiston*, even in the doctrine of the present day, would more aptly suit our comprehension, than that of oxygen. The second grand division is that of the ocean, sea or water. Here we again recognize our oxygen, not only as the principal ingredient in magnitude, being about four-fifths of the whole; but in all respects, claiming our first attention. In this water, the oxygen is further concentrated, having lost a part of the caloric which it possessed in the gaseous form; and thus, by an abstraction of more of its caloric, it must approach nearer to a state of solidity." As respects the third division—the solid, or real terrestrial portion of this material world, Mr. Hume thinks his theory of the identity of silex and oxygen is supported by a mass of evidence, and that every spot in the globe teems with examples. "There is not a rock, from the most huge and congregated lumps of matter, to the most trifling protuberance; nor is there a morsel of any mineral compound, from the brilliant gem, to the most unfruitful and degraded soil, in which, if there be an earth, a metal, an alkali, or any other salifiable or oxidable element, the saturation is not always due either to the silex alone, or to some acid, and consequently to something containing oxygen." (page 9.) Mr. Hume argues the transmutation of silex into lime; and supports his arguments by analogy, and by reference to authorities: thus, at page 23,—" From the experiments of M. Volta we are informed, that all the waters of Verona contain silex in the state of carbonate of lime, or chalk, and, agreeably to this philosopher's opinion, this substance is held in solution, by means of oxygen:" and at page 33 he refers to the Ann. de Chimie, for a variety of experiments performed by M. Vauquelin, with a view to ascertain the origin of the formation of lime in the body of the common hen, and from which the egg-shell can be derived: he quotes a passage from M. Vauquelin, which concludes thus, "if new efforts, often repeated, should be conformable to these, we must be compelled to acknowledge from them, that, during the digestion of the hen, silex is converted into lime."

* Phlogiston:—fixed fire, or the inflammable principle of Stahl. On this name, when considered as a substitute for oxygen, it may not be amiss to remark, that Mr. Edmund Hart, of Nottingham, in one of his letters on the fallacy of the doctrine of latent heat, proposes to make use of two greek words, "pur, fire, and gen, a generator," to form the word " purggen," whereby, to define that simple elementary fire, which pervades all nature; and which philosophers have mistaken for latent heat.

As the word oxygen cannot be philosophically maintained, might not the term proposed by Mr. Hart, substituting the English letter y for the u, become a tolerably expressive term for the substance now called oxygen? As a prime supporter of combustion, it would be appropriate, and if altered to pyrogen, tho sound would not be offensive to the ear accustomed to that of oxygen: the greek v, (npiilon), being changed to y in both, and in many similar words.

The remarkable similarity in the effects of oxygen and silex on the metals, is noticed at page 19; particularly that process called vitrification, "which is, in every meaning of the word, a complete saturation and oxidizement. By means of these, particularly the silex, all the metals, perhaps, with no exceptions, from being the most opaque bodies in the universe, may be rendered quite pellucid, affording a variety of the most charming tints (page 20); even the precious stones, &C., seem to derive their intrinsic value, beauty, and other excellencies, entirely from the power of silex on the metals." Tho power that it "exercises over potash, soda, and a variety of other substances, which enter into the composition of glass, is a notorious instance of its neutralizing efficacy, for no acid more completely obtunds the acrimony of alkaline bodies, and disarms them of their corrosive character." At page 25, Mr. Hume appears to indulge the idea that silex, and consequently oxygen, may be allied to electricity. "It has been noticed by several authors,

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