inch or more in diameter, which appeared to be owing to the iron, remaining from the combustion of the carbon of that part of the piece, and which, being now oxidized to a maximum, assumed the usual colour of the peroxide of that metal. "In various trials, the globules were formed very abundantly on the edge of the focus, and, in several instances, were studded around so thickly, as to resemble a string of beads, of which the largest were of the size of the smallest shot; others were merely visible to the naked eye, and others still were microscopic. No globule ever appeared on the point of the plumbago which had been in the focus of heat, but this point presented a hemispherical excavation, and the plumbago there had the appearance of black scoriæ or volcanic cinders. These were the general appearances at the copper pole occupied by the plumbago. "On the zinc pole, occupied by the prepared charcoal, there were very peculiar results. This pole was, in every instance, elongated towards the copper pole, and the black matter accumulated there presented every appearance of fusion, not into globules, but into a fibrous and striated form, like the half-flowing slag found on the upper currents of lava. It was evidently transferred, in the state of vapour, from the plumbago of the other pole, and had been formed by the carbon taken from the hemispherical cavity. It was so different from the melted charcoal, described in my former communications, that its origin from the plumbago could admit of no reasonable doubt. I am now to state other appearances, which have excited in my mind a very deep interest. On the end of the prepared charcoal, and occupying frequently an area of a quarter of an inch or more in diameter, were found numerous globules of perfectly melted matter, entirely spherical in their form, having a high vitreous lustre, and a great degree of beauty. Some of them, and generally they were those most remote from the focus, were of a jet black, like the most perfect obsidian; others were brown, yellow, and topaz coloured; others still were greyish-white, like pearlstones, with the translucence and lustre of porcelain : and others still limpid like flint-glass, or, in some cases, like hyalite or precious opal, but without the iridescence of the latter. Few of the globules upon the zinc pole were perfectly black, while very few of those on the copper pole were otherwise. In one instance, when I used some of the very pure English plumbago (believed to be from Borrowdale), white and transparent globules were formed on the copper side. "I detached some of the globules, and partly bedding them in a handle of wood, tried their hardness and firmness; they bore strong pressure without breaking, and easily scratched, not only flint-glass, but window-glass, and even the hard green variety, which forms the aquafortis bottles." Having refitted the deflagrator with new zinc coils, so as to make it act with great energy, Professor 'Silliman obtained the following results, by using plumbago upon both poles. The parallelopipeds were one-fifth of an inch in diameter, and about 1 or 2 inches long; and, when brought into contact, they trans-. mitted the fluid with a splendour even more intense than when charcoal was used. "On examining the pieces, I found them beautifully studded with numerous globules of melted plumbago. They extended from within a quarter of an inch of the point, to the distance of one-fourth or onethird of an inch all around. They were larger than before, and perfectly visible to the naked eye: They exhibited all the colours before described, from perfect black to pure white, including brown, amber, and topaz colours: Among the white globules, some were perfectly limpid, and could not be distinguished by the eye from portions of diamond." While again repeating the experiments, Professor Silliman obtained still finer results. "The spheres of melted plumbago were in some instances so thickly arranged as to resemble shot lying side by side; in one case they completely covered the plumbago, in the part contiguous to the point on the zinc side, and were, without exception, white, like minute, delicate concretions of mammillary chalcedony. Among a great number there was not one of a dark colour, except that, when detached by the knife, they exhibited slight shades of brown at the place where they were united with the general mass of plumbago. They appeared to me to be formed by the condensation of a white vapour, which, in all the experiments where an active power was employed, I had observed to be exhaled between the poles, and partly to pass from the copper to the zinc pole, and partly to rise vertically in an abundant fume like that of the oxide proceeding from the combustion of various metals. It seems possible that it is white volatilized carbon, giving origin, by its condensation, in a state of greater or less purity, to the grey, white, and perhaps to the limpid globules *. "I have already stated, that the white fume mentioned above, appears when points of charcoal are used. I have found that this matter collects in considerable quantities a little out of the focus of heat around the zinc pole, and occasionally exhibits the appearance of a frit of white enamel, or looks a little like pumice stone, only it has the whiteness of porcelain, graduating, however, into light grey, and other shades, as it recedes from the intense heat. In a few instances, I obtained upon the charcoal, when this substance terminated both poles, distinct, limpid spheres, and at other times they adhered to the frit like beads on a string. Had we not been encouraged by the remarkable facts already stated, it would appear very extravagant to ask whether this white frit and these limpid spheres could arise from carbon, volatilized in a white state even from charcoal itself, and condensed in a form analogous to the diamond. The rigorous and obvious experiments necessary to determine this question, it is not now practicable for me to make; and I must, in the mean time, admit the Upon exposing these globules to the solar focus, in a small jar of pure oxygen, Professor Silliman found, that they gave out part of their substance, viz. carbonic acid, to the oxygen. possibility that alkaline and earthy impurities may have contributed to the result." The next experiments of Professor Silliman were made upon anthracite and the diamond, by means of the oxy-hydrogen blowpipe of Dr Hare. gas. "My first trials were made, by placing small diamonds in a cavity in charcoal, but the support was, in every instance, so rapidly consumed, that the diamonds were speedily displaced by the current of I next made a chink in a piece of solid quicklime, and crowded the diamond into it: This proved a very good support, but the effulgence of light was so dazzling, that although, through green glasses, I could steadily inspect the focus, it was impossible to distinguish the diamond, in the perfect solar brightness. This mode of conducting the experiment proved, however, perfectly manageable, and a large dish, placed beneath, secured the diamonds from being lost (an accident which I had more than once met with) when suddenly displaced by the current of gas. As, however, the support was not combustible, it remained permanent, except that it was melted in the whole region of the flame, and covered with a perfect white enamel of vitreous lime. The experiments were frequently suspended, to examine the effect on the diamonds. They were found to be rapidly consumed, wasting so fast, that it was necessary, in order to examine them, to remove them from the heat at very short intervals. They exhibited, however, marks of incipient fusion. My experiments were performed upon small wrought diamonds, on which there were numerous polished facets, presenting extremely sharp and well-defined solid edges and angles. These edges and angles were always rounded and generally obliterated. The whole surface of the diamond lost its continuity, and its lustre was much impaired; it exhibited innumerable very minute indentations, and intermediate and corresponding salient points; the whole presenting the appearance of having been superficially softened, and indented by the current of gas, or perhaps of having had its surface unequally removed, by the combustion. In various places, near the edges, the diamond was consumed, with deep indentations. These results seem to indicate that, were the diamond a good conductor, it would be melted by the deflagrator; and, were it incombustible, a globule would be obtained by the compound blowpipe." Professor Silliman next subjected the Anthracite of Wilkesbarre, Pennsylvania, to similar trials. "It was consumed," says he, "with almost as much rapidity as the diamond; but exhibited, during the action of the heat, an evident appearance of being superficially softened. I could also distinctly see, in the midst of the intense glare of light, very minute globules forming upon the surface. These, when examined by a magnifier, proved to be perfectly white and limpid, and the whole surface of the anthracite exhibited, like the diamond, only with more distinctness, cavities and projections united by flowing lines, and covered with a black varnish, exactly like some of the volcanic slags and semi-vitrifications." "The anthracite of Rhode-Island is thought to be very pure, Dr William Meade estimates its proportion of carbon at 94 per cent. This anthracite I have just succeeded in melting by the compound blowpipe. It gives large brilliant black globules, not attractible by the magnet, but in other respects not to be distinguished from the dark globules of melted plumbago.” "I next subjected a parallelopiped of plumbago to the compound flame. It was consumed with considerable rapidity, but presented, at the same time, numerous globules of melted matter, clearly distinguishable by the naked eye; and when the piece was afterwards examined, with a good glass, it was found richly adorned with numerous perfectly white and transparent spheres, connected also by white lines of the same matter, covering the greater part of the surface, for the space of half an inch at and round the point, and presenting a beautiful contrast with the plumbago beneath, like that of a white enamel upon a black ground." "In subsequent trials, upon pieces from various localities, foreign and domestic (confined however to very pure specimens), I obtained still more decided results; the white transparent globules became very numerous and as large as small shot: they scratched window glass-were tasteless-harsh when crushed between the teeth, and they were not magnetic. They very much resembled melted silex, and might be supposed to be derived from impurities in the plumbago, had not their appearance been uniform in the different varieties of that substance, whose analysis has never, I believe, presented any combined silex; and neither good magnifiers, nor friction of the powder between the fingers, could discover the slightest trace of any foreign substance in these specimens. Add to this, in different experiments, I obtained very numerous perfectly black globules, on the same pieces which afforded the white ones. In one instance they covered an inch in length, all around; many of them were as large as common shot: and they had all the lustre and brilliancy of the most perfect black enamel. Among them were observed, here and there, globules of the lighter coloured varieties. In one instance the entire end of the parallelopiped of plumbago was occupied by a single black globule. The dark ones were uniformly attracted by the magnet, and I think were rather more sensible to it than the plumbago which had been ignited, but not melted." Professor Silliman, in a subsequent trial, found, that Kilkenny coal gave only white and transparent globules; an effect not likely to be produced by impurities, as this anthracite is said to contain 97 per cent. of carbon. In another experiment, Professor Silliman melted a piece of plumbago into two or three large limpid globules, and nothing remained of the original appearance of the plumbago, but a small number of black points. ART. XXI.-Celestial Phenomena, from July 1. to October 1. 1823, calculated for the Meridian of Edinburgh, Mean Time. By Mr GEORGE INNES, Aberdeen. The times are inserted according to the Civil reckoning, the day beginning at midnight. The Conjunctions of the Moon with the Stars are given in Right Ascension, instead of Longitude as formerly. * The Elements of this Eclipse are given at great length in Vol. VIII. p. 174. of this Journal. * See Vol. VIII. p. 177. 23. 20 45 50 24. 15 29 41 22 27 57 25. 4 |