This gas bined with twice as much oxygen as in muriatic acid. explodes in a heat of between 86° and 104°. Fire is produced, and the gas occupies 1 times the volume which it formerly occupied, being resolved into oxygen and oxymuriatic acid gas. I explain these appearances in the following manner :-Muriatic acid combines at a certain low temperature less intimately with two atoms of oxygen, with which it makes its escape as a gas from the liquid. In this compound the electro-chemical polarization of the oxygen is less completely neutralized than in the compound of muriatic acid with half as much oxygen in oxymuriatic acid gas. When the temperature is elevated, the muriatic acid cannot retain the whole of the oxygen; it therefore enters into a more intimate combination with one half of it, and undergoes a combustion into oxymuriatic acid, fire being evolved in consequence of the more complete electro-chemical neutralization. The other half of the oxygen is set at liberty. The separation of this portion has no other effect upon the explosion than that of increasing the volume of the gaseous mass, and consequently the energy of the explosion. This explanation appears at first sight liable to two objections. The first is, that the muriatic acid, which was here in the state of a hydrous acid, should separate from the water to unite itself in an elastic state with two proportions of oxygen less intimately combined. But it is a very common appearance when a gaseous or insoluble body is formed by the play of affinities for the liquid body to remain while the gaseous body disappears, or is precipitated from the liquid, though its formation be owing to a weaker affinity. The muriatic acid here leaves the water, which should have retained it in order to combine with oxygen, and form euchlorine. In the same way concentrated phosphoric or arsenic acid separates the much stronger sulphuric acid from its bases whenever the mixture reaches the temperature at which anhydrous sulphuric acid becomes gaseous. Chemistry can exhibit many such examples. The explanation of them belongs to a department of the doctrine of heat still unexplained, and to its relation to both the electricities. The explanation furnished here by the old doctrine affords no anomaly different from what takes place in other bodies. The second apparent objection is, that the muriatic acid combines less intimately with two portions of oxygen than it does with 'the one portion with which it constitutes oxymuriatic acid. But it is clear that, provided the same difference in the intimacy of combination takes place between other bodies in different states, this explanation will furnish no objection or improbability. I will now show that such a difference in the intimacy of compounds is a very general appearance, which takes place not only between simple bodies, but likewise between compounds, to which hitherto but little attention has been paid. When, in the year 1811, I was occupied with examining the combinations of antimony, I discovered accidentally that several metalline antimoniates, when they begin to grow red-hot, exhibit a sudden appearance of fire, and then the temperature again sinks to that of the surrounding combustibles. I made numerous experiments to elucidate the nature of this appearance, and ascertained that the weight of the salt was not altered, and that the appearance took place without the presence of oxygen. Before the appearance of fire, these salts are very easily decomposed, but afterwards they are neither attacked by acids nor alkaline leys-a proof that their constituents are now held together by a stronger affinity, or that they are more intimately combined. Their opposite electro-chemical polarity must, therefore, be more completely neutralized, by which these bodies are brought to a state of chemical indifference. The cause of the appearance of the fire, therefore, is that in a higher temperature a more intimate chemical combination, or a stronger electro-chemical discharge must take place between the bodies. Hence it follows that between the same bodies different degrees of intimacy in point of combination may subsist. From my dissertation it will be seen that I even at that time foresaw that these facts would furnish a key to explain the explosion of euchlorine. Some time after, during my short stay in London, I mentioned this appearance to Wollaston and Davy. The former observed that, to his great surprise, he had seen something similar in gadolinite.* Davy had observed the same appearance of fire on heating the hydrate of zirconia, which he ascribed to a contraction of the earth. at the instant when the water separated. Since that time I have observed these appearances in many other bodies; as, for example, in green oxide of chromium, oxide of tantalum, and oxide of rhodium. I shall take oxide of chromium as an example. Upon pulverized chromate of lead let a mixture of concentrated muriatic acid and alcohol be poured. Heat is produced, and ether, muriate of lead, and muriate of chromium, formed. Let the solution be mixed with more alcohol, in order to separate all the lead salts. Then distil off the alcohol, dilute the solution again with water, and precipitate all the oxide of chromium with caustic ammonia, adding a slight excess of alkali. Let the greenish-grey precipitate, which is a hydrated oxide of chromium, be separated, dried, and heated, in a crucible or small retort till it be slightly red-hot. Water is given out, and the oxide becomes greyish-black, or almost black. Let it now be taken from the fire, weighed, and placed in a strong heat. As soon as it becomes red-hot we shall perceive it all on a sudden become intensely ignited, and this ignition disappears almost as suddenly. Oxide of chromium, by being thus treated, loses no weight. Its colour is pale green; and instead of its easy solubility in the state of hydrate, it has become, when The appearance of fire which gadolinite displays is very lively. The variety with a glassy fracture answers better than the splintery variety. It is to be heated before the blow-pipe, so that the whole piece becomes equally hot. At a red heat it catches fire. The colour becomes greenish-grey, and the solubility in acids is destroyed. Two small pieces of gadolinite, one of which had been heated to redness, were put in aqua regia; the first was dissolved in a few hours; the second was not attacked in two months. deprived of water, difficultly soluble, and after ignition completely insoluble. In this case a new combustion takes place between the oxygen and chromium already combined; that is to say, a new electro-chemical discharge, by which the elements not only combine more intimately, but the oxygen has lost its former properties, or its former electro-chemical polarization has been exchanged for a complete electro-chemical indifference. It is clear that if the oxide of chromium at this temperature were gaseous, the production of fire would cause it to explode, without the ingredients undergoing any new combination with another body (perhaps even a separation), and without the oxide of chromium ceasing to be the same compound, and in the same proportions as before. If we could obtain chromic acid free from water, and in a separate state, probably when exposed to a higher temperature it would exhibit the same appearance of fire and separation of oxygen as takes place with euchlorine in the same circumstances. Edmund Davy found that when a neutral solution of platinum was precipitated by hydro-sulphuret of potash, and the precipitate dried in air deprived of oxygen, a black compound of sulphur was obtained, which, when heated out of the contact of air, gave out sulphur, and some sulphureted hydrogen gas, while a combustion similar to that in the formation of the metallic sulphurets appeared, and common sulphuret of platinum remained behind. In this case the very same phenomenon is observable as in euchlorine. The platinum combines at a low temperature loosely with a greater proportion of sulphur than it can retain in a higher temperature. When the compound is heated there is produced fire, because the platinum combines more intimately with a portion of the sulphur, and another portion which cannot be retained at that temperature is disengaged. I have found that when we heat the oxide of rhodium obtained from the soda-muriate of rhodium, water first comes over; and on increasing the temperature, combustion takes place, oxygen gas is suddenly disengaged, and a sub-oxide of rhodium remains behind. Here again we have the same appearance as with euchlorine. Rhodium has this in common with the base of muriatic acid that its first and third oxides are salifiable bases, while the second possesses the characters of a super-oxide, giving out oxymuriatic acid when digested with muriatic acid, and forming salts with no acid, but in some measure combining itself with the bases. The peroxide, on the contrary, is a well marked salifiable base; but its oxygen is less intimately combined. It, cannot be obtained from * If we adopt the theory, and place the electro-chemical properties of bodies in the electro-chemical polarity of their smallest parts, the first combination may be produced by the discharge of the two poles, B, C. The compound is still polar by the electricity of A and D, that is, it possesses those properties which it loses by the discharge of A, D, because the body then becomes indifferent. from the inferior oxides, as these have the oxygen more intimately combined; but is procured only at lower temperatures, and under favourable circumstances by the abstraction of the excess of rhodium.* The base of muriatic acid gives, in the same way, first an acid, then two super-oxides, then an acid, which can be procured only under favourable circumstances, and by no means directly. We have now, I conceive, fully shown that different degrees of intimacy subsist between oxygen and the same combustible basis, frequently between the same proportions. The combustible body in a low temperature often unites less intimately with a greater number of atoms of oxygen, and then at a higher temperature enters into a closer combination with a smaller number of atoms, by which fire is produced, and the excess of oxygen is set at liberty. We have seen that this difference in the intimacy of the combination takes place, not only between combustible bodies and oxygen, but likewise between other bodies, both simple and compound, as is evident from the experiments on the production of sulphuret of platinum by the moist way, on the metalline antimoniates and the siliciate of yttria. This more intimate union, then, is a general appearance, and it cannot be alleged that it has been contrived merely for the purpose of accounting for the explosion of euchlorine. It is evident, therefore, that the explanation furnished by the old doctrine agrees fully with every other department of chemical science. (To be continued.) ARTICLE V. Trigonometrical Survey of the Wide Mouth Shoal, or Royal Sovereign's Shoal, near Beachy Head, in the English Channel. By Col. M. Beaufoy. [For the Diagram see Plate L. Fig. b, c.] OBSERVATIONS made with a Hadley's sextant for determining the situation of the Wide Mouth Shoal, or the place on which some years past the Royal Sovereign man of war grounded, and was nearly lost, and which shoal is in a book of pilotage denied to exist. * See my treatise On the Cause of Chemical Proportions, Annals of Philosophy, vol. iii. p. 255. VOL. VII. N° VI. 2 F Feet. Nautic Miles. Q, H, shoal from Bexhill Church Q, B, shoal from Brightling Mill.. Q, I, shoal from Willington Mill.. .38,903 or 6'34 ..80,167.. 13.10 .....46,842.. 765 Q, S, shoal from Beachy Head Flag Staff ...40,466.. 6-61 Let M, N, be the meridian of Brightling Mill; 26 48 24 S.W. .19 21 46 S.W. Bexhill Church bears from the shoal 17° 24′ 41′′ N. E., distant 38,903 feet, or 6.34 nautic miles. Willington Mill 71° 11′ 14′′ N. W., distant 46,482 feet, or 7.65 nautic miles. Beachy Head Flag Staff 92° 37′ 35′′ W. of the N., distant 40,466 feet, or 6.61 nautic miles. Brightling Mill 8° 32′ 39′′ N.W. distant 80,167 feet, or 13.10 nautic miles. 60,851 fathoms is a degree of latitude. Q, H, 6,400 Q, B, 13,179 Nautical miles and fathoms. 7,709 Q, S, 6,660 The bearings are the true points. The shoal is of a circular form, about 500 feet in diameter, and has 13 feet water at low spring tides. It is also the outermost shoal, the Horse of Willington being much within it. Marks for finding the Shoal.-Murray's Tent on with the East |