of lead and asbestos cautiously drawn out into a beaker glass, by means of a bent iron wire, and the tube then inverted within another tube, e e, closed at one end, as shown in Fig. II. The mixture of peroxide of lead and asbestos contained in the beaker glass is now treated with a strong solution of bi-carbonate of soda, and left to stand for about twenty-four hours, with frequent shaking.* Solution of bi-carbonate of soda is also poured into the tube e e until the level of the liquid shall have reached a point, f, on the combustion-tube, a little above that which was occupied by the plug c, and this is also left to stand as the other. After the lapse of sufficient time for the reaction to be completed, the solution is filtered from the asbestos mixture, including also the solution in the tube e e, and not omitting to carefully rinse out the anterior portion of the combustion-tube. The asbestos mixture upon the filter is then thoroughly washed, the filtrate concentrated by evaporation, and the sulphuric acid precipitated with chloride of barium. The following results of analyses of bi-sulphide of carbon indicate the degree of accuracy afforded by this process. The preparation employed was commercial bi-sulphide of carbon, which was first subjected to re-distillation. Analysis 1. 0.1414 gramme of bi-sulphide of carbon gave 0.0806 of carbonic acid, and 0.8592 of sulphate of baryta. Analysis 2. 0.274 gramme of the same substance gave 0.158 of carbonic acid, and 1.6768 of sulphate of baryta. * H. Rose, Chimie Analytique, new French edition, p. 662. Analysis 3. In this analysis, in which I was prevented from determining the carbon, 0.1537 of bi-sulphide of carbon gave 0.9461 of sulphate of baryta, corresponding to 84.5 per cent of sulphur. The mixture of asbestos and peroxide of lead employed was of that which had already been used in the preceding analyses, and may possibly have contained a trace of undecomposed sulphate of lead, as the per cent of sulphur found in this case is 0.3 per cent above, while in the preceding analyses it was a fraction below the theoretical quantity. Trusting, however, that the results already obtained will be deemed sufficient to show the method to be a good one, I have not thought it advisable at this time to further repeat the analysis of this substance. I may here state that I have already applied the process in the analysis of bodies containing hydrogen, and have obtained satisfactory results which will soon be published. The important advantage thus gained of being able to determine the different elements from the same portion of substance, considering also the simplicity of the process, can hardly fail, I think, to secure for this the preference over the older methods. Five hundred and forty-ninth Meeting. March 28, 1865.-SPECIAL MEETING. The PRESIDENT in the chair. Professor Gibbs presented the following paper. Observations on Crystals and Precipitates in Blowpipe Beads. By GEORGE H. EMERSON. Believing that the subject of this article is so far novel, at least, as not to have been brought into general notice through the press, I have thought it of sufficient interest to merit publication. While studying, a few months since, the blowpipe behavior of the alkaline earths, I noticed that the opacity produced by "flaming," or exposing to an intermittent heat, a borax bead sufficiently saturated with one of the earths, was often only partial, a variable portion of the bead becoming opaque white, while the remainder was perfectly transparent. The extent of the opacity seemed dependent on the duration of the heat. Moreover, when nearly the whole surface was obscured, the interior was transparent; for, upon carefully removing the external part of the bead, a clear, vitreous nucleus was disclosed; but beads exposed to longer heat, when broken showed no trace of this vitreous interior. But just beginning the study of Chemistry, I was wholly unacquainted with the phenomena of the devitrification of glass, and did not feel well assured, therefore, that crystallization was the cause of this opacity, though it occurred to me at the time that such was probably the case. But if the change produced by flaming was a result of crystallization, then a crystalline structure ought under some circumstances to be discernible; and the density of the crystallized portion could be no obstacle, as I had already ascertained that to be variable at the pleasure of the operator, my experiments yielding results of every degree, from a translucent film to complete opacity. Although density of aggregation did not seem to stand in the way, minuteness of crystalline form might be an impediment to investigation. A borax bead charged with lime exhibited a thin, filmy band stretching across the otherwise transparent surface, when slightly heated with a fine-pointed flame; but in this I could find no crystals with a hand lens magnifying fourteen diameters. Magnesia, however, when similarly treated, gave a very different result. The bead became studded with beautiful, needle-like crystals, arranged in tufts, or fascicular bunches, and visible even to the naked eye. Several trials with the same base confirmed the fact of crystallization, and showed a surprising uniformity of crystalline form. But was this form, seemingly constant, a character whereby to recognize the earth, or would other members of the group likewise exhibit it, if properly dealt with? for the experiments with magnesia had taught me that crystals were not always obtained by flaming, an amorphous cloud being sometimes the only result. I reverted to lime; but with no success. I could get no crystals. Next, I tried baryta. The first trial of slight flaming yielded crystals, of which the hexagonal and rectangular outline could be easily seen without a glass. Sometimes a third shape was visible, looking something like an hour-glass; but these forms seemed to be constant, and there was nothing in the beads in the least resembling the magnesia crystals. Strontia, similarly treated, yielded transparent crystals of a plumose character. Three members of the group, then, had yielded crystals with borax ; and crystals possessing quite well-marked distinctive characters. Lime did not crystallize, its opacity, as seen when magnified two hundred diameters, being due to a dense aggregation of exceedingly minute bubbles. Upon treatment with microcosmic salt, lime and magnesia gave, with very slight flaming, nebulous films; that of the former being resolvable into a multitude of spicular crystals, when magnified four hundred times; and the latter into rectangular crystalline forms, in most cases, very nearly square. With the same flux, baryta gave hexagonal crystals, discernible by the naked eye; and which, when not rendered too opaque by prolonged flaming, viewed under the microscope, resembled the common stellate form of snow crystals. Strontia produced equally conspicuous crystals, but of a rectangular form, the length being twice or three times the breadth. Several experiments with each of the bases just named, in both fluxes, showing no variation in crystalline form from those I had already observed, although in every instance I submitted the result of my trials to microscopic examination, rarely using a less magnifying power than eighty diameters, I passed on to such of the other earths and metallic oxides as were within my reach, of which a list will be found upon page 481. Before describing in detail the phenomena produced by flaming with these several substances, a few words in reference to the methods pursued may not be unacceptable; premising, however, that these statements, together with all included in these pages, are not predicated upon sufficiently numerous experiments to be regarded as authoritative; and that they are offered rather as suggestions to persons better fitted, and with more ample leisure and opportunity than the author, to follow out the subject exhaustively. The loop of platinum wire should be about one eighth of an inch in diameter, and quite circular, in order to give as uniform convexity to the surface of the bead as possible. Two turns of the wire are better than one where microcosmic salt is used, on account of the greater fluidity of this flux than borax. The bead should not be much over one twentieth of an inch thick at least, where examination by a high magnifying power is desirable. Crystallization is best produced by thrusting the tip of the blowpipe well into the flame of the lamp, until a fine-pointed jet of flame, less than an inch in length, is obtained; then expose a small portion of the bead, close to the edge, (see diagram,) for an instant to its action, until the part so exposed, and the wire immediately adjacent, become of a dull red heat, when the too long, the suspended matter being then so rapidly precipitated as to prevent crystallization. The bead should in such cases be subjected to the action of a powerful flame till perfect transparency is obtained, and, if the first mentioned be the difficulty, a little more of the flux added before again flaming. It seems to make little difference with the earths whether the glass containing them be prepared in the oxidating or reducing flame, previous to flaming, though they are most readily dissolved at the point of greatest heat; but the oxides of the non-volatile metals give the best results when the bead is charged in the oxidating, and, after cooling, subjected to the action of a fine-pointed reducing flame. One advantage of using this small fine-pointed flame is, that only a portion of the bead is subjected to the reducing influence; and as the heat is maintained but an instant, the portion of the glass fused is not only circumscribed, but superficial, so that the reaction takes place where it can easily be observed. Moreover, a devitrifying action goes on, at the same time, in the unfused but reheated portion of the bead.* I shall use the term "intermittent flame" to distinguish the ordinary process of flaming from that just described. The amount of the substance used varies, of course, with the subject of the experiment, although the formation of striæ in the glass, As the method of treating beads just described in the text promises to be of value, in certain of its applications, in the arts, as well as of scientific interest, the author intends to secure such applications by patent, after having made some additional experiments. |