a very thin coating upon silica, and the whole is so light that the pieces float upon water. That the metal obtained is not silicon (supposing silicon to be a metal) is obvious from this, that the lustre is neither altered by water, nor nitric acid, nor muriatic acid, nor nitromuriatic, even when in contact with these liquids for 24 hours. Whereas silicon, as we learn from Davy's experiments, cannot be obtained in a separate state, because it decomposes water and every other liquid which he applied to it. I fused a little of the matter sent me with potash, before the blow-pipe, in a platinum forceps. The bead had a greenish shade, and contained a little iron, which was the only metal I could discover in it. But I rather think the metallic lustre is connected with the oil. I have frequently obtained charcoal from animal oil, having a metallic lustre little inferior to that exhibited by the specimens sent me with the preceding communication. The fine silvery colour is probably owing to a very thin coat of this charcoal covering the white silica.-T. VIII. Septaria. By Wm. Davis, Esq. (To the Editors of the Anuals of Philosophy.) GENTLEMEN, In the Annals for January, page 39, is an interesting paper on the uses of the Septaria; after reading which, I immediately turned to the new edition of Thomson's Chemistry, 1817, for further information, but without success; for I could not find any one of the names, septaria, ludus helmontii, or loam-stone, in the index to that valuable work. You would confer an obligation, therefore, on some of your readers, if you would refer us to the proper article for information, or give in your Annals such a description as would enable us to determine whether that valuable substance occurs in our own neighbourhood. At the same time I beg leave to inquire what is the best means of preventing the oxidizement of steel, or brass wire, when exposed to water? My view in asking this question is the improvement of wire "gig-mills," used for dressing, or facing woollen cloth. The wires act on the cloth something like a brush, or comb, and are constantly wetted. I am, Gentlemen, Your obliged servant, WILLIAM DAVIS. Gloucestershire. In answer to the first query of our correspondent, we reply that the septaria are balls mostly in the form of an oblate spheroid, which, on being broken, appear to be composed of brownish, or bluish indurated clay, intersected by veins, or partitions (septa) of calcareous spar. These veins are widest about the centre of the ball, and generally terminate a little short of the surface. Hence, they have probably been produced not by infiltration, but by a spontaneous separation of the original ingredients composing the mass of which the ball was formed. The septaria occur either in beds, or casually dispersed through the mass of the great deposit of blue clay which lies above the chalk. The deep cutting for the archway at Highgate Hill, the canal in the Regent's Park, and the clay pits between London and Hackney, exhibit sections of this stratum; as also do the cliffs at the Isle of Sheppy, and at Southend, on the opposite shore of the Thames. The space between the South Downs and the central chalk ridge of the Isle of Wight is chiefly occupied with the same deposit. Septaria also exist in other beds of slaty clay lower in the series than the chalk. They bear a great analogy also with the balls of argillaceous iron ore, deposited in the shale between certain beds of coal; and probably these ironstone balls would answer many of the purposes of the genuine septaria. With regard to the latter query of our correspondent, we fear that it will be impossible to prevent either iron or brass wire from being corroded when exposed to a constant alternation of air and of moisture.-ED. IX. New Comet. Dr. Olbers, of Bremen, has just discovered a new comet, Nov. 1, at seven p. m. in the west shoulder of Serpentarius, between the stars K and No. 104 of Bode. It was small and very brilliant, particularly in its centre, without a visible nucleus, or tail. It cannot be seen without the telescope. At 7h 14' its right ascension was 253° 13', its northern declination 9° 14', its course was directed from E. to S. (Quoted from Gazette d'Aix-la-Chapelle, in Journ. Phys. Nov. 1817.) X. Chemical Analysis of Pimento. M. Braconnot has subjected this substance to an elaborate examination, the result of which is, that it consists of the following ingredients: 1. Fecula. 9.0 1.9 2. A very acrid oil. 3. Waxy matter united to a red colouring principle. 0.9 4. A peculiar gummy matter. .... 5. Animalized matter. 6. Citrate of potash ... 7. Insoluble residue 6.0 5.0 6.0 67.8 3.4 100.0 M. Braconnot has performed some experiments on lichens, and particularly on a species of variolaria, probably the faginea, the constituents of which are stated to be the following; the particular details are not given, and the analysis is obviously 5. Uncrystallizable saccharine matter. very imperfect; but it may deserve to be noticed in consequence of the large proportion of lime which was detected in the sub stance: 1. Matter analogous to wax. 2. Bitter and acrid principle 3. Green colouring matter... 4. Undetermined pulverulent substance. 6. Jelly.. 5.0 2.0 1.0 3.0 0.5 4.4 7. Vegetable matter analogous to the preceding.. 31-0 34.0 9. Lime, which was intimately united to the pre- 18.0 10. Ferruginous phosphate of lime, and loss... 1.1 100.0 XI. Meteorological Establishment at St. Bernard. In the number of the Bibliotheque Universelle for October last, Prof. Pictet gives an interesting account of an establishment that has lately been formed for making meteorological observations at the Convent of Great St. Bernard. Every attention appears to have been paid to the accuracy of the instruments, and the method of using them; and we may expect to derive the most important information from a detailed account of the state and variations of the atmosphere at an elevation of above 8,000 feet, where the mean height of the mercurial column is not more than 22 inches. With respect to the construction of the instruments, we are informed that the reservoir of the barometer is exactly ten times the diameter of the tube; the correction for the changes of the height of the mercury in the reservoir, is, therefore, only of the variation in the tube, a quantity which is, in almost all cases, too minute to be noticed. To the barometer is attached a mercurial thermometer furnished with two divisions, one octogesimal, according to the scale of Reaumur, the other so arranged that each degree of the scale corresponds to of a line of variation in the height of the barometrical column. The zero of this latter answers to the tenth degree of the octogesimal scale (54.5° of Fahrenheit), and every observation of the barometer is reduced to this constant temperature, by means of the correction which is obtained by the thermometer. The correction is very easily made, since every degree above or below zero represents so many tenths of a line, which are to be subtracted or added from the barometrical observation. The thermometer is formed with a flattened column of mercury, so as to present to the eye a large and very visible surface, while at the same time the absolute size is very minute. The hair hygrometer of Saussure is employed, but with a little alteration in its mechanical arrangements; in the old construction the index descended towards dryness, and ascended towards moisture; in the present instrument the motions are reversed, so that its action is rendered more conformable to that of the barometer and thermometer. We have an account of the observations that were made in this meteorological observatory during the latter half of Sept. 1817. The greatest height of the barometer The mean height at sun-rise Ditto at 2 P.M... .... 22.40 22.06 22.36 22.42 54.5° 29.75 The greatest height of the thermometer. Mean height of the thermometer at sun-rise 38.00 46.6 Mean height of the hygrometer at sun-rise.. 92.0 84.3 There were four rainy days during this period; the quantity of rain was no more than 7 inch: the season is represented as having been peculiarly fine. XII. Researches on the Cerealia. By M. Vogel. M. Vogel read a memoir on this subject to the Royal Academy of Sciences at Munich, in March last; the following are the principal results which he deduces from his experiments; but the processes are not detailed by which they were obtained. 1. The farina of the wheat of triticum hybernum is composed 4. Carbonic acid gas will not supply the place of yeast and leaven in fermentation. Hydrogen will make the dough rise, but will not make it ferment. 5. The constituent parts of farina, when they have been once separated, cannot be reunited, so that the farina should become proper for making bread. 6. Wheaten bread is composed of XIII. State of the Magnetic Needle at Paris. Feb. 10, 1817, at one p. m. the variation of the magnetic needle was 22° 17′ W. This observation, compared to those of the two preceding years,* seems to leave no doubt of the retrograde motion of the magnet. March 14, 1817, two p. m. the inclination of the needle was 68° 38'. The same instrument in Oct. 1810, was 68° 50'. (Ann. Chim. Dec. 1817.) XIV. Mr. Howard's Work on Meteorology. Mr. Luke Howard will shortly publish, in two volumes, a work entitled, "The Climate of London, deduced from Meteorological Observations made at different Places in the Neighbourhood of the Metropolis." Vol. I. will contain an introduction relative to the construction and uses of several meteorological instruments; tables of observations for ten years, with notes and results ; accounts of collateral phenomena in other parts of the world, and occasional dissertations. Vol. II. will contain a methodical account of the climate of London, under the several heads of the winds, barometer, temperature, rain, evaporation, electricity, &c. deduced from the facts contained in the first volume; with copious general tables, and an index to the whole work. To which will be added, "An Essay on the Modifications of Clouds," by the same Author, several times heretofore printed. The variation of the needle at Paris, Oct. 12, 1816, was 22o 25' W. (Ann. Chim. Dec. 1816.) |