was the first to point out this fact with regard to alloys, in a paper on the alloys of antimony and zinc. He showed that those containing 43 to 64 per cent. of zinc all crystallize in the same form, but differently from the other alloys. With the alloys of gold and tin it has been shown that well-defined crystals are not limited to definite proportions of the constituents, but are common to all gold and tin alloys containing from 27 to 43 per cent. of gold; and that crystals and mother-liquor never are of the same composition. Storer has also experimentally proved that all the copper and zinc alloys crystallize in the same form. These facts show that the crystalline alloys of carbon and iron do not prove the existence of chemical combination between them, more especially when we consider that several definite crystalline compounds of carbon and iron have been obtained. In all probability, by altering the conditions of cooling, &c., crystals of iron containing various amounts of carbon may be obtained from the same sample of cast iron. For the chemical combination theory of cast iron we have (1) The evolution of carburetted hydrogens when white cast iron is treated with dilute acids. (2 The existence of definite crystalline forms of carbon and iron. Against it (1) The analogy of the alloys of carbon and iron with the other alloys. (2) The fact of carbon in such a fine state of division that it may exist in white iron (solidified solution) and may be able to unite with hydrogen at the moment of being set free (as in the case of platinum-silver alloys, where a portion of the platinum is dissolved by nitric acid). (3) We know of no other case where with two elements the different rates of cooling determine the chemical combination or decomposition (conversion of white into grey and grey into white cast iron). (4) That with alloys definite crystalline forms are not necessarily chemical combinations. That iron in a molten state will not dissolve more than about 5 per cent. of carbon is analogous to the cases of lead and zinc, bismuth and zinc, mercury and zinc. For it has been shown that pure lead will only dissolve 1.6 per cent. a pure zinc, and pure zine 1-2 per cent. of pure lead; that pure zinc will only dissolve 2.4 per cent. pure bismuth, and pure bismuth from 8.6 to 14.3 per cent. pure zinc§. Now, although no actual determinations have been made, we may suppose that the solvent power in the above-mentioned cases of the one metal for the other at higher temperatures will be greater than at lower ones; hence, for instance, zinc (containing a small percentage of lead) might possibly be made to crystallize from a molten alloy of lead and zinc, containing, say, from 2 to 2.5 per cent. zinc. Supposing the metals lead and zine be melted together in equal parts, what takes place? The zinc (according to the temperature) takes up a certain amount of lead, and floats upon the lead which has taken up a certain amount (according to the temperature) of the zinc. If these two alloys were intimately mixed together (by stirring or shaking) and cooled rapidly, we might suppose that under certain conditions an almost homogeneous mixture might be obtained; or supposing we were rapidly to cool a solution of zinc *Memoirs of the American Academy (new series), vol. v. p. 337. Ibid. p. 430. § Ibid. in lead, we should produce a solid mass similar to what we termed a solidified solution. Again, if only a few per cent. of tin be added to the mixture, of, say, ten parts zinc in lead, a perfect alloy will be formed. : Applying these facts to the alloys of carbon and iron, we are led :(1) To look upon white iron (containing small percentages) as a solidified solution of carbon and iron; (2) When containing larger percentages as a solidified solution of carbon and iron, with carbon diffused through the mass in a very fine state of division; (3) When containing large percentages of carbon, together with certain other substances (manganese, to wit), as a solidified solution of carbon, iron, and the other substances. And to look on the grey modification as a solidified solution of carbon and iron, with carbon (varying amounts of the graphitic modification) mechanically intermixed. Another point in favour of the above may be mentioned, namely, that it has been observed that the conducting-power of the pure metal may be deduced from that of the impure one, where the conducting-power of the impure metal differs from that of the pure one by not more than 20 per cent.; this has been found to hold good only in cases where solidified solutions exist. Now some experiments have been made in this direction with various kinds of iron. The results obtained were as follows:: The amount of impurities in 5, 6, 7 were, in 100 parts,— These data show that the alloys of iron follow in this respect the same laws as those of other metals. *Phil. Trans. 1864, p. 369. To see whether the above assumptions, as to the chemical nature of cast iron, are correct, it is proposed (1) To make some pure iron. (2) To alloy the pure iron with various amounts of carbon and to test the physical and chemical properties of these alloys. (3) To alloy the pure iron in different proportions with other metals and metalloids. From the forgoing considerations I expect to be able to produce analogous alloys to iron and carbon with some of the other metals, having the peculiar properties of cast iron, steel, and wrought iron; and probably some may be found to be much better adapted for certain purposes than the alloys of carbon and iron-for instance less liable to become crystalline by age, &c. (4) To alloy the pure iron with various amounts of carbon, and to add to these alloys such substances as are found in the commercial irons so as to study their respective effects on the physical and chemical nature of cast iron, and more especially on their influence on the solvent power of iron for carbon. It is intended to investigate carefully the action of dilute and strong acids on the various alloys of iron and carbon, in order to see how far, and under what conditions, the carbon is evolved as carburetted hydrogen. The experiments will be made on a small scale, fusion taking place in one of Deville's oxyhydrogen furnaces, which gives an admirable means of experimenting with refractory metals. The pure iron will partly be prepared from the oxalate, and partly by the electrotype process, and fused in lime crucibles. The experiments have already been commenced, and I hope at the next Meeting of the Association to report good progress. Report on Observations of Luminous Meteors, 1865-66. By a Committee, consisting of JAMES GLAISHER, F.R.S., of the Royal Observatory, Greenwich, Secretary to the British Meteorological Society, &c.; ROBERT P. GREG, F.G.S., &c.; E. W. BRAYLEY, F.R.S., &c.; and ALEXANDER S. HERSCHEL, B.A. THE Committee have the satisfaction to present in their Report a marked degree of progress over their success in former years: Observations of three large meteors, at the Royal Observatory, Greenwich, have been confirmed by descriptions of observers at distant places, so that the height and velocity of the meteors could be conclusively determined (Appendix I. 1, 2, 4); and the accounts of meteors continually communicated by observers to the Committee have led in other cases to obtaining the same satisfactory result. The Committee are particularly indebted to Mr. Warren De la Rue for a collection of excellent descriptions of the detonating fireball of the 21st of November 1865, placed by Mr. Warren De la Rue at the disposal of the Committee, by which the earth-distance, the velocity, and the direction of this meteor in space could be determined. Exact determinations of the height, and other particulars of large meteors in different parts of the globe, are collected in this Report, following the Catalogue, in Appendix II. Remarkable statements regarding the large detonating meteor which appeared over the Dover Straits on the forenoon of the 20th of June 1866, with instrumental measurements of its apparent path by Mr. Francis Galton, will be found in this Appendix. The object of the Committee in providing star-charts to observers of the meteoric shower of November last, was attained; and accurate observations of luminous meteors under that date are presented in the Catalogue of the Report. The radiant-point of the meteoric shower, during the period of its greatest activity, was situated within two degrees of the place which it occupied in the interval of the greatest meteoric activity of the same shower in the year 1833-a fact in itself demonstrative of the fixed uranographical character of the phenomenon (Appendix IV. 2). The height of the November meteors is shown in this Report to be the same as that of ordinary shooting-stars, or about sixty miles above the surface of the earth; whilst with regard to their speed, they are three times swifter than those meteors which at the same time arrive from the direction of the constellation Taurus. Bearing in mind the strong probability that exists of the occurrence in the present year of a more extraordinary meteoric shower, on the morning of the 13th or on the morning of the 14th of November, than any that has yet been observed at the English observatories, the Committee during the past year judged it unadvisable to incur avoidable expense, or to exceed the means at their command by lithographing the charts of general radiant-points of shooting-stars, exhibited two years ago at Bath, to the Meeting of the British Association, and these they now suggest might be printed, and distributed with advantage. The occasion of the return of the great November shower being one of very rare occurrence, the Committee, with the view of profiting by the opportunity thus afforded of observing the spectra of luminous meteors, have this year provided themseves with spectroscopes, and have succeeded in analyzing the light of shooting-stars by means of their prismatic spectra. Two spectroscopes were directed to be prepared by Mr. Browning, and were first used on the 10th of August last, and seventeen spectra were observed. A description of the observations, together with the discovery of the yellow sodium-line as the chief feature of the greater number of the train-spectra, will be found in the last Appendix of the Report. |