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This augmentation varies, too, a great deal, from one metal other. We remark that tin, thallium, cadmium, zinc, lea found together towards the upper part: at about 200° and 230 resistance has doubled. Still above them are found steel and the resistance of the latter has doubled at 180°, quadrupled at at 860° is about nine times as great as at zero. Palladiur platinum, on the contrary, approach the axis of the temperat it is only in the vicinity of 400° and 450° that the augmen has acquired a value equal to that of the primitive resistance. copper, silver, form an intermediate group. It may therefo said generally that, the less elevated the fusing-point of a meta more rapidly does its conductivity diminish: iron and steel an exception to this law. In alloys the variation is always than in the metals which constitute them. In certain of (German silver for example) it is very slight; and this rer them valuable for the construction of standards and resistanceApproximately, it is in the metals in which the resistance is g est that its increase, under the influence of heat, is relatively most rapid. The slight differences of composition which alte profoundly the absolute resistance, have but a feeble influence the relative value of its augmentation by rise of temperatur Bibliothèque Universelle, Archives des Sciences Phys, et Nat., vo pp. 284-287.

ON THE CONSERVATION AND THE PROPERTIES OF A PLATE OF P LADIUM SATURATED WITH HYDROGEN BY ELECTROLYSIS.

R. BÖTTGER*.

The Author has found that it is only after being heated to red that a plate of palladium, charged with hydrogen by electroly loses the hydrogen which it held by occlusion. This is reac ascertained by immersing the plate in a solution of ferridcyanide potassium. In fact, as long as hydrogen is still present at the s face of the palladium, reduction of the ferridcyanide into fer cyanide is observed, which is easily recognized by means of properties of the salts of protoxide of iron.

There are also other metals which thus absorb electrolytic drogen-as nickel, zinc, and cobalt.

When a plate of palladium is coated with palladium-black becomes saturated with hydrogen much more rapidly. If wh thus saturated it is wrapped in gun-cotton, the latter explodes the end of a few seconds, and the plate burns during five or minutes with a flame of feeble brightness.

A plate of palladium charged with hydrogen and left in the a loses in time the gas occluded. Placed under water deprived air, under absolute alcohol, or ether, it loses at first a part of hydrogen with effervescence, but retains the rest without appare change. Bibliothèque Universelle, Archives des Sciences, vol. li. p. 18

M. L. de la Rive, by a sudden and very great diminution of the conductivi nevertheless bismuth and antimony form an exception, and become, on t contrary, better conductors on melting.

* Pogg. Ann. Jubelband, p. 150.

[graphic]

LONDON, EDINBURGH, AND DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

[FOURTH SERIES.]

FEBRUARY 1875.

XI. Studies on Magnetism. By E. BOUTY, Professor of
Physics at the Lycée of Rheims*.

UP

P to the present time there does not exist a complete theory of the magnet. Notwithstanding the relative simplicity of the phenomena presented by soft iron, one could not expect to explain these apart; and the study of steel magnets is still too little advanced to supply the elements of a satisfactory physical theory.

Such being the situation, I thought that an experimental and close investigation of the phenomena presented by steel magnets (e. g. those accompanying their production, union, or separation) would not be devoid of interest. The present is a first attempt in this direction. The questions which form the subject of it, though hitherto very little studied, would yet offer numerous numerical verifications for any accurate theory of magnetism ; and this would suffice to render highly important researches of the sort we have undertaken.

Most of the investigations the subject of which has been magnetization by currents refer to soft iron. Lenz and Jacobit, Joule‡, Müller §, Wiedemann || especially, and more recently Quintus Icilius, Stoletow **, and Rowland †† preoccupied themselves with determining the magnetic moments, temporary or perma

* Translated from a copy, communicated by the Author, of a Thesis presented to the Faculty of Sciences, Paris, 1874.

† Pogg. Ann. vol. xlvii. (1839). † Phil. Mag. S. 3. vol. ii. (1839).

§ Pogg. Ann. vols. lxxix. & lxxxii. (1850, 1851).

|| Ibid. vols. c., cvi. & cxvii. (1857-1862).

Ibid. vol. cxxi. (1864).

** Phil. Mag. January 1873.

†† Ibid. August 1873.

Phil. Mag. S. 4. Vol. 49. No. 323. Feb. 1875.

G

nent, developed by a current of given intensity in a bar placed in the axis of a spiral excited by the current. Several of these physicists treat also, subsidiarily, the same question for steel. As regards the accessory phenomena accompanying magnetization, they are so numerous and varied that they constitute an inexhaustible mine which still, notwithstanding numerous labours, has scarcely been touched. We will cite only those memoirs which have the closest connexion with the subject of the present investigation.

Quetelet* studied the magnetism produced in a bar of steel by friction with a magnet. He established that the magnetism increases, up to a certain limit, with the number of the frictions, according to precise laws, to which we will return by-and-by. Hermann† and Scholzt, under the direction of Frankenheims, proved an analogous augmentation when a bar of steel is brought near the pole (free or covered with paper) of an electromagnet, or when a steel bar is several times introduced into a spiral traversed by a current.

Coulomb ||, and afterwards Lamont, in their numerous studies on all branches of magnetism, have enriched the science with observations on the influence of the temper of steel upon its moment of saturation, and on the phenomena which accompany the union or separation of superposed magnetized plates. Villari**, and long previously Abriatt, made some experiments on the brief duration of the phenomenon of magnetization.

The temporary magnetization of steel, observed for the first time by Musschenbroek and Epinus, has been the subject o interesting memoirs by Poggendorff‡‡ and Wiedemann §§.

But the most complete investigation we possess on steel magnets is found in the recent labours of M. Jamin ||||. These researches which it is not our duty to estimate here, open to physicists = path in some sort quite new, and in which we should be happ to have made one step.

I. METHODS OF MEASUREMENT.

The determination of the magnetic moment of a magnet i most frequently effected by one of the two methods indicate

* Ann. de Chim. et de Phys. Ser. 4. vol. liii.

† De naturali magnetismo in Chalybem inducendo quanto momento s tempus. Vratisl., 1865.

† Quanti sit momenti tempus in fluidi galvanici intensitate adhibita. § Pogg. Ann. vol. cxxiii.

Magnetismus.

magnetismo inducendo, certa quada Vratisl., 1863.

|| Mémoires de l'Académie, passim. ** Pogg. Ann. 1873.

†† Annales de Chimie et de Physique, Ser. 3. vol. i. # Pogg. Ann. vol. xlv.

§§ Galvanismus, vol. ii.

|||| Comptes Rendus de l'Acad. des Sciences, 1873-74.

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