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then dissolved by water; but the dark coloured particles which were diffused through it, acted upon the water of the solution; so that when an attempt was made to collect them upon a filter, they were for the most part converted into silica. Some gas was produced by the action of this substance upon the water, but it does not appear to have been collected and examined.

In another experiment of this kind, the substance was heated with hydrate of potash; there was a copious effervescence, and silica appeared to be reproduced and dissolved by the alcali. In another instance, the product was heated in a strong lixivium of potash, the solution acquired an olive tinge, but there was scarcely any perceptible effervescence, from which it is probable that the basis of silica, like boron, is soluble in alcaline dotations without decomposing them. Indeed, Sir I!. remarks that this substance has in many respects a close alliance to boron. It appears to be neither fusible nor volatile; like boracic acid, its oxide exerts a neutralizing power on the alcalies, and forms like that acid vitreous compounds with the alcaline earths; and like boron, the siliceous basis forms a powerful acid when combined with fluorine. Sir II. thinks it probable that these substances form a distinct class, not allied to the metals, as he formerly supposed, but arranging themselves according to their natural affinities, probably between charcoal and sulphur, and phosphorus.

This paper contains also some additional experiments on chlorine, made with a view to the determination of the still agitated question of its simple or compound nature; but they afford no evidence whatever of its containing oxygen. Sulphuret of lead was kept some time in a state of fusion in chlorine; the results were sulphurane, (Dr. Thomson's liquor,) and plumbane, or muriate of lead, but not an atom of sulphate of lead was formed; which must have been produced if oxygen had been present. Plumbane was heated in sulphuric acid gas, and also in carbonic acid gas, but no change whatever was produced.

The other facts or remarks on this subject tend to prove that no water is formed by the action of muriatic gas on ammonia; and that the small quantity which appears during these experiments, is the minute quantity which is known to exist in these gases, but which is not essential to their existence, nor chemically combined with them.

Some Experiments and Observations on a New Substance which becomes a Violet-coloured Gas by Heat. By Sir Humphry Davy, Knt. LL..D. F.R. S. The singular substance described in this paper, was discovered by M. Courtois, a manufacturer of saltpetre, at Paris. He had remarked that some of his metallic vessels were very rapidly destroyed in the processes requisite to extract soda from the ashes of sea weeds. In searching for the cause, he discovered the substance in question, by which he ascertained that the corrosion of his vessels was produced. This substance is obtained very readily from the kelp ashes, after the soda is obtained from them, merely by the action of sulphuric acid. If the acid is concentrated, the heat produced is sufficient to raise the substance in the state of vapour, which is of a fine violet colour, and which when condensed, forms crystals, having the lustre and the colour of plumbago.

Shortly after its discovery, a short memoir was read to the Institute, by Clement and Desormes, describing its principal properties; and it has since engaged the attention of some of the most eminent experimental chemists. They ascertained that its specific gravity is about four times that of water; that it assumes the gaseous state at a temperature below that of boiling water; that it combines with the metals, with phosphorus, and sulphur; and likewise with the alcalies, and metallic oxides; that it forms a detonating compound with ammonia; that it is soluble in alcohol, and still more so in ether; and that by its action upon phosphorus and hydrogen, a compound having the characters of muriatic acid, is formed. Gay Lussac, in another paper read to the Institute, stated that the acid produced by its combination with hydrogen, was a new and peculiar one; and he regarded the substance as allied to chlorine.

In subjecting this body to experimental investigation, Sir H. began by endeavouring to ascertain if argentane (muriate of silver) would be formed by its action upon nitrate of silver. For this purpose, it was purified by distilling it from lime, and when it was added in solution, to a solution of nitrate of silver, a dense precipitate of a pale lemon colour was formed. This precipitate being collected and examined, was fusible at a low red heat, and then assumed a red colour. It was rapidly decomposed by fused hydrat of potash, and a substance having all the characters of oxide of silver, was formed. When this was separated by a filter, the solution being acted upon by sulphuric acid, aQbrded the peculiar substance. A solution of potash being boiled on the precipitate, afforded the substance when treated in the same manner by sulphuric acid. The precipitate was much more rapidly acted upon by light, than the muriate of silver.

As these facts rendered it probable that the precipitate was a compound of the newly discovered substance with silver, Sir H. endeavoured to form a direct combination of them with each other. For this purpose, some of the substance was introduced into the closed end of a curved glass tube, and a portion of silver foil was placed in the upper part of the same tube. The foil was heated nearly to redness, and the vapour of the new substance being passed over it, an immediate combination took place, and a fusible substance was formed, in all its obvious characters the same as that obtained from the nitrate of silver. Supposing the new substance to be capable of decomposition, Sir H thought it most likely to be effected by the action of the highly inflammable metals upon it, or by the action of chlorine, which in general disengages oxygen from its combination with inflammable matter. Some potassium was therefore heated in a small glass tube, and some of the new body in a state of vapour was passed over it; as soon as they came in contact, there was inflammation, and the potassium burnt slowly with a pale blue light. When the experiment was made in a mercurial apparatus, no gas was disengaged. The substance resulting from its combination with potassium, was white, fusible at a red heat, and soluble in water; its taste was peculiarly acrid; and when acted upon by sulphuric acid, it effervesced, and the new substance was disengaged. In this experiment there was evidently no decomposition effected.

It was next exposed to the action of chlorine in a small glass tube. The chlorine was absorbed, and the resulting compound was a yellow solid matter, volatile by heat, and soluble in water, the solution being of a yellowish green colour, and strongly acid. When the solution was acted upon by a solution of potash not in excess, it effervesced and afforded the peculiar substance. The acid formed by this combination with chlorine, reddened vegetable blues by its immediate contact, and soon after destroyed them entirely. The new substance heated in oxygen gas, or brought into contact with red hot hyperoxymuriate of potash, appeared to suffer no change. Sir H. heated the new substance with iron, mercury, tin, zinc, and lead, out of the contact of air: it combined with them without any violent action, and formed compounds fusible at a moderate heat, and volatile at a higher temperature. All these compounds, except that of zinc, which was white, were of different shades of red, brown, and orange; and that with mercury, when crystallized, was a bright crimson. The combination with iron, when exposed to the action of an alcaline solution, deposited black oxide of iron; but when heated in a retort with ammonia in the gaseous state, it combined with the ammonia, and the compound volatilized without leaving any oxide. The combination with tin was soluble in water, and had the character of an acid, and it formed combinations with the alcalies without depositing any oxide. The crimson coloured combination with mercury, united in the same manner to potash without decomposition; the addition of sulphuric acid to the combination, separated the compound of the substance with mercury, and sulphat of potash was formed.

The new substance combines with phosphorus with great rapidity at the temperature of the atmosphere, producing heat without light. A strongly acid gas arises from the mixture, the quantity of which is increased by the application of heat. When the new substance is in excess, a red coloured compound is formed, which is easily fusible and volatile, but when the phosphorus is in excess, the product is more fixed. The gaseous acid which it forms by combination with phosphorus, produces dense white fumes by combining with the aqueous vapour of the atmosphere; its odour resembles that of the solid compound of chlorine and phosphorus, which is very analogous to that of muriatic acid. It is rapidly absorbed by water. With ammonia it forms a dense white salt, from which sulphuric acid separates the peculiar substance, and the odour of hydrogen is at the same time perceptible. When mercury is heated in this acid gas, the same compound is formed as when that metal is combined directly with the new substance, and hydrogen equal in volume to half that of the gas is disengaged. It affords similar results with potassium ; that metal is converted into the same compound as is produced by the direct combination of potassium with the new body, and a gas having the properties of hydrogen, is disengaged, equal to half the volume of the acid gas.

Of the two compounds which this substance forms with phosphorus, that which is volatile and easily fusible, readily dissolves in water when assisted by heat, and affords a strong acid, which, when evaporated, leaves hydrophosphorous acid; but, if neutralized by potash and acted upon by sulphuric acid, affords the peculiar substance. The other combination, which is with difficulty fusible, is acted upon by a small quantity of water, and heated in a glass tube, a spontaneously inflammable gas is disengaged, and a white sublimate is formed, which becomes hot when it is brought into contact with cold water, and affords a considerable quantity of hydrophosphoric gas. The solution of this crystalline substance in water, neutralized by potash, and decomposed by sulphuric acid, yields the peculiar body; but if the solution is heated strongly before it is neutralized, hydrophosphoric acid alone remains, which, when heated, gives off hydrophosphoric gas, and is converted into phosphoric acid. As this acid is formed by the combination of the peculiar substance with hydrogen, the existence of hydrogen in the phosphorus, or of hydrogen or water in the substance itself, must be inferred. This inference is rendered more probable by the fact, that when the substance is previously distilled through quick lime, so as to separate all its moisture, the gas is produced in very small quantity, but is greatly increased when the substance is moistened. Sir H. therefore thinks the production is principally occasioned by the aqueous moisture which adheres to it, though the small proportion of hydrogen contained in the phosphorus, may influence the result in some degree. The gas which is obtained by the distillation of the fusible compound with water in small quantity, is similar to that obtained during the formation of the compound while it is heated; and when absorbed by water, they both afford, when acted upon by nitrate of silver, the product already noticed as being formed by the action of the substance itself in solution, upon that salt

.Sir II. attempted to form a direct combination of the substance with hydrogen, by heating it to redness in a glass tube filled with that gas. When the gas was moist, or any aqueous vapour was present, a strong acid liquid, of a deep yellow colour, was formed; but when care was taken to exclude the presence of moisture, there was an expansion of volume, and when the tube was broken, the gas-which was set at liberty, precipitated the nitrate of silver in the same manner as that produced during the union of the substance with phosphorus. The acid thus produced by the union of this substance with hydrogen, has a very strong affinity for water; and a large quantity of the gas is absorbed by a very small quantity of water. It is evaporated with the water by heat; and in its liquid state it dissolves the substance rapidly, and becomes of a tawny colour.

The French chemists Desormcs and Clement, had announced the ready solubility of this new body in solution of potash; and Sir H. by carefully investigating the changes which accompany this combination, discovered the singular and curious fact, that by this combination a class of substances, analogous to the hyperoxymuriates, are formed. When the solution is evaporated and the product heated to redness, a substance precisely similar to the compound of the new body with potassium, is produced; but this combination can only take place by displacing the oxygen of the potash, and Sir H. found that the oxygen remained in a state of triple combination with the potassium and the new body. If the substance is dissolved to saturation in a moderately strong solution of potash, a considerable quantity of crystals fall down, and by evaporating the remaining solution, an additional quantity is obtained. The spontaneously formed crystals, are but little soluble in water, have a taste similar to that of the hyperoxy

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