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violet colour. We may observe, however, that gas, as used in the title of this paper, has rather a tendency to mislead; for that word is generally employed to denote permanently elastic fluids, vapours incapable of condensation per se by any known means, and only to be obtained in a solid or liquid form by combination with water, or other bodies. The substance here in question is capable of crystallizing per se; and is not found in its aëriform state at the ordinary temperature of the atmosphere.

The discovery was made by a manufacturer of saltpetre at Paris, M. Courtois. In some of his processes for procuring soda from sea-weed ashes, he found his metallic vessels corroded; and, upon inquiring into the reason of it, he found that if sulphuric acid, concentrated, is poured on the ashes after the carbonate of soda is extracted, the heat produced by the combination expels a vapour of a fine violet colour, which condenses in crystals resembling plumbago. To denominate this a gas, may at first seem as inaccurate as it would be to give this name to the smoky vapours or fumes of sulphur, which often assume a blue tinge. But, if we rightly understand this paper, the vapour from the new substance has a different appearance-not rising in opaque streaks, but in one uniform and transparent elastic medium. It is different from gases only in being so easily condensed; and may, perhaps, be termed a gas condensable at a low temperature.

Sir Humphry Davy being at Paris soon after this substance had begun to attract the attention of men of science, undertook a course of experiments, with a view, first, to ascertain whe ther it was in reality a new and simple body, incapable of decomposition; and next, what were its peculiar properties. A suspicion having been entertained, that the acid which it forms by its action upon phosphorous and hydrogen, is muriatic acid, from the resemblance of its properties, our author was naturally led also to the settlement of this question. His experiments have not, perhaps, added much to the knowledge of the subject obtained at its first discussion by the inquiries of Messrs Decarmes and Clement, who read a paper upon it at the Institute, (or as Sir H. Davy, writing in last January, terms it, the Imperial Institute of France), last November; and M. Gay-Lussac, who read another memoir in the succeeding month. But he has fully established the fact of this being a new and simple sub

* If a red-hot iron is held in sulphurous acid gas, or common carbonic acid gas, where the former generally exists, fine bluish va pours rise round it by the decomposition.

VOL. XXIII. No. 46.

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stance; and his experiments are, in many incidental points, very interesting to the lovers of chemistry. We shall therefore proceed to give an account of their results,-although it is announced that a more full investigation may soon be expected from M. Gay-Lussac, who is still occupied with inquiries into the nature of the substance.

The author's first object was to ascertain its relationship with muriatic acid, suggested by the circumstance already mentioned, of its forming, with phosphorus and hydrogen, an acid resembling that hitherto mysterious substance. Having thoroughly purified the solution by distillation from lime, and then mixed it with a solution of nitrate of silver, a yellowish precipitate was thrown down. This being fused, became red; and being decomposed by hydrate of potash, gave an oxide of silver, and a matter solved, or rather suspended in the water, from which, when collected by the filtre, the exhihition of sulphuric acid produced the violet-coloured gas. When the precipitate was in like manner boiled in potash solution, it afforded the substance, if the same acid was applied: nor had it any appearance, in other respects, of muriate of silver; on the contrary, it had all the characters of a compound of silver and the peculiar substance, formed by melting them together; and may therefore be safely allowed to be such a compound.

The suspicion respecting muriatic acid being thus in a great measure removed, our author proceeded analytically, and attempted the decomposition of the substance, by means of substances having a strong attraction for oxygen and chlorine, (the term used by him, as our readers may remember, for oxymuriatic acid), and by substances having a strong attraction for the bases that attract oxygen. If, as was supposed probable, the body contained either oxygen or chlorine, these substances would either attract or precipitate the bases in question. The substances that most strongly attract oxygen and chlorine, are the new alkaline metals; and the chlorine itself is the substance chiefly remarkable for precipitating oxygen from its union with inflammable bases.

The first experiment instituted with a view to precipitate the supposed base to which oxygen might be united in the substance, is one of the most interesting that occurs in the course of the inquiry, at least if we rightly comprehend a material part of it which the narrative leaves rather doubtful. Potassium (the metallic base of Potash) was heated in a glass tube, and the substance was passed over it in vapour. As soon as the vapour came in contact with the metal, there was an inflammation; metal burning slowly with a pale blue light,-and no gas was disengaged. The substance formed was white, fusible, and

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soluble. When sulphuric acid was applied to it, an effervescence took place, and the violet-coloured gas was evolved. Our author infers from this examination, that the white substance was merely a compound of the potassium and the peculiar body which had remained undecomposed. We could have wished that he had more distinctly stated the absence of oxygen gas in the experiment, and that no potash was formed by the process. We should suppose it was so: and what is mentioned afterwards of heating other metals out of the contact of air,' with the substance, confirms the supposition. An expression used further on, gives additional weight to the construction here put on the process: For the author speaks, referring to that process, of the combustion of potassium in the vapour of the substance. Here, then, is a very remarkable phenomenon, not with relation merely to this new body, but throwing no small light upon the general theory of combustion. It is a complete case of combustion without oxygen. We took occasion many years ago, (see Vol. III. p. 24.), to point out the exceptions to the new or antiphlogistic theory, arising from cases of light and heat, produced without the presence of the gas which that theory deems to be their peculiar formation. We could then only refer to experiments, wherein ignition, or light and heat, issuing from bodies in their solid or fluid states, was exhibited. The wellknown experiment of fusing sulphur and iron in vacuo, is the most remarkable instance. Their union evolves much heat and light: The mass is in a red, or even white, heat, though no air whatever, nor any substance containing oxygen is present. The ignition of bodies which attract none of the base of oxygen gas seemed another case of the same kind. But an example was wanting of flame so produced, that is, ignited vapour; of bodies, for example, uniting in the state of gas, without oxygen, and giving out light and heat in that union. Some time afterterwards we noticed an apparent case of a flame thus produced (Vol. VI. p. 100.) in the experiments of some Italian chemists: but it seemed to be of rare and uncertain occurrence in their process; and, having excited little of their attention, it could not with any kind of safety be relied on. We therefore suggested a very practicable form of experiment, by which such an effect might be produced; namely, by means of an apparatus then described, in which zinc, a volatile metal, should be exposed to heat in vacuo, and its fumes or vapour made to meet those of sulphur. Our expectation was, from the former experiment on the union of sulphur with a fixed metal, that this combination would produce a real flame without oxygen gas. Now, the experiment of Sir Humphry Davy has precisely done

so in another manner; or rather, by exhibiting vapour of a different kind to a very combustible metal, still without oxygen. The violet gas and potassium in contact, with heat applied to them, unite, and there is a flame formed during their union. In one respect this is more contradictory to the new French theory, than the process suggested by us: for we intended that the heat should supply volatility to both the solid bodies: whereas, here, one of them only is made aeriform by heat; and its contact with the other in a heated state also, but not volatilized by the heat, increases its disposition to take the state of gaseous fluidity exactly as oxygen gas does; and light and heat are given out during the combination of the two bodies, both in vapour. This is therefore as complete an example as could be desired, of inflammation produced by a vapour or gas different from oxygen gas, and in the very same manner in which that gas produces flame. But we return to the more immediate subject of investigation.

Chlorine united with the substance, and did not at all decompose it: oxygen gas and oxymuriates did not at all affect it. The formation of metallic oxides by its union with metals, mentioned by the French chemists, appears to be entirely the effect of moisture, or other accidental admixture of bodies containing oxygen; for when metals, as iron, zinc, tin, mercury, &c. were heated without any air, and thus exhibited to the new substance, they united without any violent action; and when the compound was examined by reagents which contained no oxygen, as ammonia, there were no traces found of oxides.

This substance unites readily with phosphorus; and their combination evolves an acid gas of a pungent odour, and peculiar properties. Its smell resembles that of muriatic acid; but on examination it is found to contain no such acid, nor any other. It is a compound of the new substance and hydrogen. Hence arises the question, how the hydrogen is furnished? Does it come from the new body, or from the phosphorus, or from some water present in the experiment? By distilling the substance through quicklime, almost all moisture was separated; and in this case the acid gas gave much less hydrogen than before, until moisture was added, when the hydrogen again became abundant. From some other particulars related by the author, it seems improbable that any sensible supply of the hydrogen could come from the phosphorus; although certainly electrical expe riments detect a minute portion of it in that body.

Potassium inflames in muriatic acid gas; but this being, according to the French theory, an acid, and supposed to contain oxygen, would be deemed no exception.

But no part of this inquiry deserves more attention than the experiment repeated after the French chemists, on a solution of the substance in potash, which rapidly unites with it, forming a brown compound. When this is evaporated, and the residue heated to redness, there remains a substance seemingly the same with that formed by uniting potassium with the substance. In this process oxygen is given out, evidently the oxygen of the potash, as the author observes. But it is singular that he does not observe, that his own great discovery of the decomposition of the alkalies might thus have been made in an easy and simple way, had he never succeeded in decompounding those bodies by the electrical process. The accidental circumstance of the saltpetre manufacturer finding the new substance among his pots and kelp, would have led to this, one of the most bril. ian scientific exploits in our times, by one or two simple steps. One of the first experiments which the chemist would have made, must have decomposed the alkalies;-for M. Courtois had accidentally stumbled upon a substance, which happens to have so extraordinary an affinity for inflammable bases, that it unites greedily with them, and precipitates the oxygen with which they were previously combined in apparently indissoluble union. This is perhaps the only instance in which mere chance, without any investigation, was even very near leading to a grand philo sophical discovery: but it is not, by a hundred, the only case in the history of science, in which satisfactory proof is afforded, that if one man, or one accident, or one inquiry, had not led to a discovery at a particular time, the step would have been made soon after by other means. The history of maritime discovery especially, is full of such examples.

The union of the new body with potash, led the author to discover a class of substances, exactly resembling hyperoxymuriates in their qualities, and formed in a similar manner. The oxygen of the potash unites with a portion of the substance and a portion of the metallic base, while the remaining portion of that base unites with the remaining portion of the new substance, without any oxygen. The reader will easily perceive the close analogy between this process, and the decomposition and recomposition by which hyperoxymuriates are formed. The triple compound crystallizes, detonates wherthrown on burning coals, and deflagrates with charcoal; its taste also reren.bles that of hyperoxymuriate of potash. The binary compound does not crystallize or detonate; and is indeed the same body as that formerly described to result from uniting potassium with the new substance. When sulphuric or nitric acids are exhi bited to the triple compound, part of the oxygen unites with the

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