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figure, analogous to some which have been before noticed; there being on some of the crystals only one of the planes b replacing each of the solid angles on which two are placed in the drawing, and these being the alternate planes. Many of the crystals present, however, the pairs of planes b, as shown in the figure.

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Carbonate of Magnesia.

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The crystals from which this figure has been given, I have received from M. Teschemacher. The primary form is an oblique rhombic prism, which may be cleaved, but not distinctly in the small crystals I have attempted to operate upon, parallel to the planes M and M'.

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Sulphate of Cinchonia.

Mr. Pope, of Oxford-street, has favoured me with some minute crystals of this salt: from which the primary form appears to be a doubly oblique prism, having cleavages parallel to all its planes. The cleavage, however, parallel to P is not very distinct. Some of the crystals are of the form I have given, but there are others whose figure does not appear to be immediately related to it. These are probably hemitrope, or rather quadruple crystals, united by secondary planes; but they are not sufficiently distinct in character to enable me at present to trace their precise relations to the primary form.

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ARTICLE X.

On the Property which some Metals possess of facilitating the Combination of Elastic Fluids. By MM. Dulong and Thenard.*

PROF. DÖBEREINER, of the University of Jena, has discovered one of the most curious phenomena which physical science is susceptible of unfolding. We are unacquainted with his labours excepting by the announcement in the Journal des Debats of the 24th of August last, and which does not give a very correct account of them, and from a letter of M. Kastner to Dr. Liebeg, which the latter, now at Paris, has communicated to us. In this it is stated, that platina† in a spongy mass occasions the combination of oxygen and hydrogen at common temperatures, and that the extrication of heat which results from the action renders the metal red-hot. We were anxious to verify so surprising a fact, and found it perfectly correct. As the experiment may be made with the greatest ease, we shall perform it before the Academy.

Not being acquainted with the researches which the author of this beautiful experiment has undoubtedly undertaken in order to develope the theory of it, we could not refrain from making some experiments with this view; and although we have not yet succeeded, we think that the results of the observations which we have already made are not unworthy the attention of the Academy.‡

In the experiment which we have made, the spongy platina became red-hot when placed where the hydrogen escaping from the reservoir became intimately mixed with the air. It was evident from this, that detonation would occur by immersing a piece of the spongy platina in a mixture of two volumes of hydrogen and one volume of oxygen; and this was confirmed

* Annales de Chimie et de Physique, tome xxiii. p. 440.

Since the printing of this notice, the authors have observed first, that palladium in a spongy mass is capable of inflaming hydrogen as platina does; secondly, that iridium in the same form became very hot, and produced water; thirdly, that cobalt and nickel in mass, at about 572° Fahr. effected the union of hydrogen and oxygen; fourthly, that spongy platina at the common temperatures formed water and ammonia with nitrous gas and hydrogen, and acted upon a mixture of hydrogen and protoxide of azote.

The hydrogen lamp invented by M. Gay-Lussac is extremely convenient for performing this experiment. The electrophorus is to be removed, or the conductors are merely to be detached; a piece of light spongy platina is to be placed at the distance of about two centimetres from the aperture at which the gas escapes; when the cock is turned, the jet of hydrogen gas comes mixed with atmospheric air to the surface of the spongy platina. It then soon became red-hot, and the hydrogen gas once inflamed continues to burn as it escapes, as if it had been lighted by the spark.

In the absence of the lamp, the common apparatus used for preparing hydrogen gas may be employed. It is however requisite to take care that the gas passes through a very small aperture, in order that it may more intimately mix with atmospheric air.

by experiment. If the proportions of the gaseous mixture differ much from those which form water, or if an incombustible gas, such as azote, be present, the combination goes on slowly, the temperature is but little increased, and water soon condenses in the receiver.

If the spongy platina be strongly calcined, it loses the property of becoming red hot; but in this case, it effects the combination of the two gases slowly, and without any very sensible increase of temperature. Platina reduced to a very fine powder, by well-known chemical means, does not act upon the gases even slowly, at common temperatures, nor do platina wires or bars. The agreement of these observations may give rise to the idea, that the porosity of the metal is an essential condition in the production of the phenomenon ; but the following facts disprove this conjecture.

We reduced platina to leaves as thin as the malleability of the metal would allow of. In this state, the platina acts at common temperatures upon the mixture of hydrogen and oxygen, and the action is more rapid when the foil is thinnest. We obtained some which effected the detonation in a few seconds. But what renders this action still more extraordinary is the physical condition indispensable to its production. A very thin sheet of platina rolled on a glass cylinder, or freely suspended in a detonating mixture, produced no sensible effect after a lapse of several days. The same sheet of platina, if crumpled, acts instantaneously, and causes the mixture to detonate.

The leaves disposed as we have described, and which produce no effect at common temperatures, the wires, powder, and thick bars of platina, which are inefficient under the same circumstances, act slowly, and without producing explosion at a temperature of 400° to 572° according to their thickness.

We have found that other metals possess the same property as platina. The very remarkable fact discovered by Sir H. Davy during his researches on the safety lamp, viz. that wires of platina and palladium at a low temperature become bright-red when immersed in a detonating mixture, having appeared to us to be derived from the same cause as the phenomenon under discussion, we were first induced to try palladium.

The piece which we made use of was given to one of us by Dr. Wollaston, and consequently must be considered as free from alloy; nevertheless we were unable to reduce it to very thin leaves, as it cracked under the hammer. We attribute to this circumstance its possessing no action at the temperature of the atmosphere; but it acted at least as well as platina of the same thickness at a high temperature. Rhodium being brittle could not be subjected to the same preparation; but it occasioned the formation of water at a temperature of about 464° of Fahr. Gold and silver in thin leaves act only at high temperatures, but always below that of boiling mercury. Silver is less power

ful than gold. A bar of gold acts, but with greater difficulty than the leaves; a thick bar of silver acts so feebly as to be questionable whether it has any power.

We have examined whether other combinations could be effected by the same method. Oxide of carbon and oxygen combine, and nitrous gas is decomposed by hydrogen at common_temperatures by spongy platina; thin sheets of this metal require a temperature of above 572° of Fahr. to cause the two former gases to combine. Gold leaves effect it also at a temperature approaching that of boiling mercury.

Lastly, olefiant gas mixed with a proper quantity of oxygen is completely converted into water and carbonic acid by spongy platina, but only at a temperature above 572° of Fahr. It will be remembered on the subject of the preceding experiments, that one of us proved a long time since, that iron, copper, gold, silver, and platina, possess the property of decomposing ammonia at a certain temperature, without absorbing any of this alkali, and that this property appeared to be inexhaustible. Iron possesses it in a greater degree than copper, and copper more than silver, gold, or platina, the surfaces of all being equal.

One hundred and fifty-four grains of iron wire were sufficient to decompose within a few hundredths a current of ammoniacal gas rather rapidly evolved, and continued during eight to ten hours, without the temperature exceeding the limit at which ammonia completely resists. Three times the quantity of platina wire of the same size scarcely produced an equal effect, even at a higher temperature.

The remarkable results of this experiment depend perhaps upon the same causes as those which occasion gold and silver to effect the combination of hydrogen and oxygen at 572° Fahr.; platina in mass at 518° Fahr.; and spongy platina at common temperatures. Ifthen we observe that iron, which so readily decomposes ammonia, does not effect, or effects with difficulty, the combination of hydrogen with oxygen, and that platina, which is so powerful in the latter case, scarcely decomposes ammonia, we are induced to suppose that some gases have a tendency to combine under the influence of the metals, and others to separate; this property varying on account of the nature of each. Those metals which produce one of the effects most perfectly are incapable of producing the other, or in a less degree.

We shall refrain from offering the conjectures which these singular phenomena have given rise to, until we have completed the experiments which we have undertaken to verify them.*

* Prof. Döbereiner's experiment has also been verified by Mr. Faraday, who has given the following notice of it in No. 31, of the Journal of Science. "It consists in passing a stream of hydrogen against the finely divided platina, obtained by heating the muriate of ammonia and platina. In consequence of the contact, the hydrogen inflames. Even when the hydrogen does not inflame, it ignites the platina in places; and I find that when the hydrogen is passed over the platinum in a tube, no air being admitted, still the platinum heats in the same manner.

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ARTICLE XI.

Notice of some newly discovered Islands in the Arctic Sea. By Capt. Duncan: communicated in a Letter from L. Edmonston, Esq.

SIR,

(To the Editor of the Annals of Philosophy.)

Zetland, Balta Sound, Sept. 12, 1823. THE public attention has been recently so much directed to Arctic discoveries, that I flatter myself the following communication may be acceptable to your journal.

The Greenland ship Dundee, of London, arrived here on the 10th inst.; and her very enterprising Commander, Capt. Duncan, obligingly furnished me with the following information which is contained almost verbatim in his diary." Sept. 2, in lat. about 68° 40′; long. 24° 30′ W; foggy weather and east winds (latter part of the day clearer) blowing very fresh. Ship running in north-west towards the land; at 9, a. m. got within two miles of a small island bearing north-west, which I named Sayers Island, after the master of the Harmony, of Hull, then in company; the mainland running about NNE and SSW, distant about fourteen miles. The nearest headland on it in right bearing north, I named Cape Despair, distance six leagues. Cape Barclay of Scoresby's Chart, bore north-east and east, distance 50 miles; and the most southern headland on the main bore west and by south, distance 60 miles: this I named Duncansby Head. All the mainland seen from the ship between this point and Cape Barclay, I named Gales Land, in compliment to my owner. About 10 miles south-east from Duncansby Head, there is a low flat island which I termed Robison's Island, after the ship's managing agent. Here we lay to, hoping to see fish, but fell in with none; and the sea setting in heavy towards the land, and the wind blowing fresh, we stood off to the south.

"At noon latitude observed 68° 41'; long. 24° 30' W; by the bearings of Cape Barclay; sounded in 100 fathoms water; rocky bottom. Saw all this new land for twenty-four hours; the Harmony, of Hull, in company all the time; but the gale and sea prevented any attempts at landing. Had intended prosecuting investigation further southwards, but the lateness of the season, and the unfortunate accident of being beset nearly two months this summer, made all thoughts of such a view imprudent."

Gales Land, Capt. Duncan states, resembles in general appearance the south side of Scoresby's Sound. It is very high, and precipitous quite to the sea shore. The mountains running in ridges south-east and north-west, but their peaks are not so

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