4th April, 1831.

THE WEEKLY EVENING MEETINGS of the Members of the Royal Institution will be resumed on Friday the 15th instant, at half-past Eight o'Clock, and will be continued on each succeeding Friday evening till the end of the Season.

The following are the Arrangements of the Lectures which are to be delivered on each day at Three o' Clock in the Afternoon :

CHEMICAL AND NATURAL PHILOSOPHY. By MICHAEL FARADAY, Esq., F.R.S., F.G.S., Corr. Memb. Royal Acad. Sciences Paris, Director of the Laboratory of the Royal Institution, &c. &c. To commence on Thursday, the 14th instant, and to be continued on each succeeding Thursday till the 5th of May. The following are the Subjects of the Course :—April 14th, Optical Decep tions-April 21st, Lithography-April 28th, Flowing of Sand-and May 5th, Caoutchouc.

GEOLOGY. On some of the most important points in Geology. By THOMAS WEBSTER, Esq., F.G.S. To commence on Saturday, the 16th of April, and to be continued on each succeeding Saturday till the 21st of May.

POETRY AND THE POETS. BY JAMES MONTGOMERY, Esq., Author of The World before the Flood,' Pelican Island,' &c. To commence on Tuesday, the 26th of April, and to be continued on each succeeding Tuesday till the completion of the Course, on the 31st of May.

ACOUSTICS. BY ROBERT WILLIS, M.A., F.R.S., Fellow of Caius College, Cambridge. To commence on Thursday, the 12th of May, and to be continued on each succeeding Thursday till the completion of the Course, on the 16th of June.

BOTANY. On Vegetable Physiology and Botany. By JOHN LINDLEY, Esq., F.R.S. and F.L.S., Prof. of Botany in the University of Lond., and Assist. Sec. Hort. Soc. To commence on Saturday, the 28th of May, and to be continued on each succeeding Saturday till the completion of the Course, on the 18th of June.

The Sons and Daughters of the Members of the Royal Institution, under Fifteen Years of Age, may be admitted on payment of half the sum for each Course.

Syllabuses of the Lectures may be obtained at the Royal Institution.

OF

THE ROYAL INSTITUTION

OF

GREAT BRITAIN.

ON CERTAIN PHENOMENA RESULTING FROM THE ACTION OF MERCURY UPON DIFFERENT METALS.

BY J. F. DANIELL, F.R.S., AND M.R.I.

THE results of the following experiments on the action of mercury upon different metals may probably be considered interesting; not only on account of the novelty of the facts, which have been hitherto, I believe, unnoticed, but from the relation in which some of them may be found to stand to the laws of molecular attraction.

EXPERIMENT I.

A piece of flexible metallic tube, which is composed of an alloy of tin and lead, was partly immersed in mercury contained in a wine-glass. In the course of a few days it was examined, and found studded with brilliant metallic crystals, in a line coincident with the level of the fluid. After this examination, it was replaced and left undisturbed for six weeks: at the expiration of which period it was carefully lifted out of the mercury; and a considerable groupe of well-defined crystals were found loosely adherent to its upper part, and many similar ones floating upon the surface of the mercury. Their form was that of hexahedral plates variously modified; some of them were above one-tenth of an inch diameter, and their lustre was white and silvery. By placing them in a small inverted cone of paper, perforated at its apex, the fluid mercury drained from

VOL. I.

Ост. 1830.

B

them, and they were left in nearly a dry state. The tube was dissolved away at its lower end to a thin edge, and the action of the mercury had evidently decreased as it ascended: the upper part to which the crystals were attached was but little acted upon, so that, in its whole length, it gradually tapered downwards. The substance of the metal, even above the part immersed, was saturated with mercury, and had become very brittle.

Hence it appears that the action of the mercury upon the alloy was, first to saturate its pores and disintegrate its substance, forming a brittle, uncrystallized compound which it must have subsequently dissolved. The amalgam thus produced, being of less specific gravity than the fluid metal, floated to its surface, where the attraction of cohesion between the particles of the compound, being greater than the attraction which held them in solution in the fluid, caused them to crystallize. I have formerly* remarked, that if a mass of any soluble salt be carefully suspended in water, it will be more acted upon at its upper than its lower end, and will assume, more or less, the form of a cone, with the apex at the surface of the liquid. The particles of water which are in immediate contact with the salt, combine with a portion of it, and thus becoming specifically heavier than the remainder, sink to the bottom of the vessel; others succeed and follow the same course. A layer of saturated solution is thus deposited, which increases in depth as the process advances, protecting in its rise that part of the mass which is covered with it from further action. In the present instance the process is directly the reverse: the solvent, by union with the solid, becomes specifically lighter, and the saturated solution is first formed upon the surface; and the action continuing longest at the bottom of the mass, a cone is produced with its apex downwards.

EXPERIMENT II.

A piece of pure tin, in the usual form of closely-aggregated imperfect prisms, in which it is found in commerce, was partly immersed in mercury, and left undisturbed for a month. Upon

* Journal of the Royal Institution, vol. i, p. 24. 1st Series.

examination, a large cluster of crystals, similar to the preceding, was found adhering to its upper part, and others floating upon the liquid. They were not quite so large as the first; but bore very distinctly the form of six-sided plates. The whole mass was thoroughly saturated with mercury, but had been more acted upon at the bottom than the top of the portion immersed. At the lower end, the prisms had the appearance of being more detached from one another than in their original state, from cracks which had taken place in the metal; and which conferred upon their extremities the semblance of imperfect pyramids. Several deep clefts also had been formed along the more prominent edges of the mass.

EXPERIMENT III.

A small bar of lead was plunged, for about half its length, into some mercury contained in a test-tube. Having been left undisturbed for ten days, it was carefully lifted out and examined. A bundle of very delicate, silver-white, feathery crystals was found loosely adhering to it, on a line with the surface of the fluid. Their form could not be accurately determined, but they resembled a heap of frosty particles swept together on a pane of glass; and their minute prisms appeared to be attached together at angles of sixty degrees. The bar had been most acted upon at its lowest extremity: it was thoroughly impregnated with mercury throughout its substance, but had not totally lost its ductility. After the operation, the tin crumbled to pieces under a slight blow of the hammer, but the lead could be flattened into a plate.

EXPERIMENT IV.

A bar of zinc was treated in the same way, and for a like period. It was found, upon examination, studded throughout the whole length which had been immersed with very bold crystals, of the form of hexahedral plates, which increased in quantity and size from below upwards. The bar tapered downwards to a point, and was more unequally acted upon than the former metals, its surface being rough, and corroded into cavities. Some of the crystals adhered very strongly to the surface, and

some of them had the appearance of being partly imbedded in the bar, or dissected from its substance. They were of a darker hue, and more brilliant than the crystals from lead and tin.

EXPERIMENT V.

A bar of fine silver was partly immersed in mercury, as in the preceding cases: at the expiration of a fortnight no crystals had been formed. The mercury had entered into its substance, but upon trial it had not lost its malleability. It was replaced, and at the end of six weeks had not apparently changed its characters. The test-tube, with its contents, was now heated till the mercury began to boil, and was set by to cool gradually. In twenty-four hours' time the bar was again examined, and a bundle of very fine needle-crystals was found clustered round the part which was just intersected by the surface of the liquid.

In this case, the affinity of the mercury for the silver enabled it to penetrate its pores, and thoroughly to saturate it, but its attraction for the resulting compound was not sufficiently strong to allow it to overcome the remaining attraction of aggregation, and dissolve the solid at the ordinary temperature of the air. When assisted, however, by heat, the solution was effected, and the compound, as in the former instances, being specifically lighter than the pure fluid, floated to the top, and crystallized.

EXPERIMENT VI.

A small portion of a bar of fine gold, about an inch and a half in length, was put into mercury, in which, of course, it sank, from its greater specific gravity. The fluid very quickly penetrated it, and completely destroyed its yellow colour. In a month's time it retained its malleability, and a part of it was flattened under the hammer into a very thin plate. Its surface was studded with very minute crystals, whose dimensions were too small to be determined. The gold was then heated in the mercury to the boiling point of the latter, when it was completely dissolved, and a pasty amalgam formed.

There can be no doubt that in all these instances the mer