to B. After having stood some time, till it has acquired the temperature of the surrounding air, the stop-cock, G,`is turned, and the elastic gum-bottle, D, containing a pretty strong solution of caustic potash, is screwed on at the bottom, as represented, in such a manner that no air be suffered to exist in it. The cock, H, is then turned, and the caustic potash introduced into the instrument, and well shaken, till all the carbonic acid is supposed to be absorbed; it is then returned into the bottle, and the stop-cock, H, secured. The instrument is then transferred to the stand, F, and the cock, H, again opened under water in the vessel, E, which rising shows the quantity of carbonic acid contained in the analyzed air, care being taken to raise or depress the instrument till the water stands exactly at the same height on the inside as the outside of the stem. The bladder used on this occasion contained about 300 cubic inches, and the number of expirations was always six, which were made as nearly as possible in an uniform manner, both with respect to time and depth. From some experiments made with mercury, and also expressly with the view of ascertaining the quantity of carbonic acid absorbed by the water used in the experiment, I have reason to conclude that the quantity, upon an average, amounted to about one-tenth per cent. This quantity, accordingly, has been added to all the numbers originally found by the instrument. As this source of er was general and uniform, it is obvious that the results were comparatively affected by it. Other sources of error, which I am well aware are very numerous, were carefully guarded against by every possible attention to those circumstances in which they were most likely to take place. ARTICLE III. On the Method of separating Iron from Manganese. By Charles Hatchett, Esq. F.R.S. &c. DEAR SIR, (To Dr. Thomson.) Mount Clare, Roehampton, Sept. 25, 1813. In the last Number of your Annals of Philosophy I have remarked a paper entitled "Contributions towards a Chemical Knowledge of Manganese, by Dr. John," first published in Gehlen's Journal für die Chimie, &c. in which the author states Gehlen's method of separating iron from manganese by succinic acid, and also his own process performed by means of oxalic cid. I am therefore induced to communicate to you a very Simple and easy method of perfectly separating manganese from iron, &c. which I have for many years employed in various experiments and analyses, although I have not hitherto had occasion to state it in any publication. SECT. I. A solution of any ore of manganese having been made as usual in muriatic acid, and filtrated, inust be diluted with three or four parts of cold distilled water. To this diluted solution add gradually pure ammonia, occasionally stirring the liquor until the acid has become perfectly neutralized; a few drops of ammonia may then be added; so that the liquor shall very slightly restore the blue colour to litmus paper which has been reddened by acetous acid. The ferruginous precipitate must then be separated by filtration, and the liquor which passes will be found devoid of colour, and contains the pure manganese in permanent solution. It affords a white precipitate with prussiate of potash, and the oxide of manganese may be obtained by evaporating the solution to dryness, and by expelling the muriate of ammonia by heat; after which, if any of the muriate should be suspected to remain, it may be separated by washing the oxide upon a filter. SECT. II. Pure oxide of manganese may be also obtained by adding ammonia in considerable excess to the cold diluted muriatic solution, which then, without loss of time, must be poured upon a filter of one fold. The liquor which passes becomes in a few minutes turbid and brownish, a pellicle is formed, and in about 24 hours the greater part of the manganese separates spontaneously in the state of brown oxide; and if the remaining liquor be evaporated to dryness and heated, the whole of the oxide will be obtained. But the objection to this method is that the manganese is so rapidly separated from the ammoniacal solution, that it is scarcely possible, even by the quickest filtration, to prevent some part from being deposited on the filter, so that it becomes again mixed with the precipitate of iron, alumine, &c. The effects of ammonia on the green oxide of iron are well known; but I do not recollect any instance of this oxide being found conjoined with manganese; and therefore it is not likely to interfere with the process above described. When ammonia in great excess is added to the neutralized solution (Sect. I ), the same effect is produced as in Section II., and the manganese is spontaneously deposited. Exposure to air does not appear to be necessary, for the mixture of the neutralized liquor (Sect. I.) and ammonia becomes turbid in close vessels. If nitric acid be added to the neutralized liquor (Sect. I.) previous to its being supersaturated with ammonia, the manganese is not more speedily separated, and in some experiments the nitric acid seemed rather to retard that effect. I need scarcely mention, that in cases of analyses, if any alumina, or calcareous earth, &c. should be suspected to have become mixed with the precipitated oxide of manganese, they may be readily separated by digestion in very dilute nitric acid. If a mixture of the neutralized solution of manganese and of green muriate of copper be supersaturated with ammonia, as in Sect. II, the manganese separates, as already described, the copper remaining in solution; and if the liquor be evaporated to dryness, the copper may be taken up and separated from the oxide of manganese by digesting the residuum in warm amI am, dear Sir, monia. Yours very sincerely, ARTICLE IV. Mineralogical Observations. By Robert Jameson, Esq. F.R.S.E. Regius Professor of Natural History in the University of Edinburgh. THE mineralogical investigations I have been engaged in for some years past have enabled me to make several interesting observations. The following short enumeration contains a few of the most important of these : : 1. That primitive rocks contain no mechanical deposites, the conglomerated rocks in gneiss and porphyry being entirely of chemical nature. 2. That greywacke is always a pure chemical deposite, and contains no mechanical intermixture. 3. That felspar occurs more abundantly in nature than is generally supposed, this mineral being one of the principal constituent parts of granite, gneiss, clay slate, porphyry, sienite, serpentine, finty slate, hornstone, greywacke, transition slate, striped jasper, oldest conglomerates, besides forming in some degree the basis of most of the primitive, transition, and floetz trap rocks. 4. That the vast beds of conglomerate which rest upon, and sometimes probably alternate with, transition rocks, are also chemical deposites. 5. That sandstone in many instances appears to be a chemical deposite. 6. That many of the fragments and fragmented appearances which occur in porphyry, limestone, and trap rocks, are of a chemical nature, and of cotemporaneous formation with the rocks in which they are contained. 7. That true primitive veins, those confined to primitive rocks, whatever may be their nature or magnitude, are often of cotemporaneous formation with the rocks they traverse. 8. That many of the veins in transition and floetz countries, even those extending for many hundred yards, and of great width, are of cotemporaneous formation with the rocks in which they are contained. 9. That strata of crystallized rocks may appear to run beneath an older rock when they really rest upon it, and have been formed after it. 10. That the various wavings in the strata of gneiss, mica slate, clay slate, greywacke, transition slate, and sandstone, are the effects of crystallization. 11. That the general, physical, and geographical distribution of petrifactions in the crust of the earth does not correspond with that of the present existing races of animals and plants. ARTICLE V. Some Mineralogical Observations on Cornwall. By Thomas Thomson, M.D. F.R.S. (Continued from p. 253.) IN the rapid sketch of the south of Cornwall, which was printed in the last Number of the Annals of Philosophy, I have described nearly every part of the county that appears demonstrably to belong to the transition class of rocks. I suspect, indeed, that this class of rocks extends considerably farther north than I have been able to trace it: nor would it be surprising if the whole of the county should be hereafter proved to be transition; but as I observed no facts to support this opinion, we cannot at present adopt it. The road from Merazion to Penzance winds along the seashore, and no rocks are to be seen till you reach the north end of the latter town. Here a bed of blue stone is perceived |