. gree. b is es at the oxygen of all the bases being equal to one half of that of the silica. Green Malacolite from Bjormyresoeden, in Dalecarlia. 54:08 containing oxygen 27:20 6.59 4.45 2.28 Protoxide of manganese 0:61 99.67 54.55 containing oxygen 27:45 5-68 5.90 1.85 Alumina 0:14 Oxide of manganese .. 0.73 99.02 53.36 containing oxygen 26.84 6:23 3.95 1.93 0:09 98.01 Green Sahlite from Sahla. sparks with the steel, but with difficulty. It is in a high degree 54:86 containing oxygen 27.59 6:62 6:38 1.00 Manganese 0.42 Alumina 0:21 a | porc was of and slight 99.99 The composition of this malacolite is, if 4 per cent. of protoxide of iron are not taken into consideration, the same as those of the first division. Before the blowpipe also, its properties are completely like them. There occur, however, at Sahla other kinds of sahlite, which, though similar in external appearance to this, are quite different in their chemical properties and composition; while the sahlite just now described, and all other malacolites of this composition, are easily fusible before the blowpipe, these are almost entirely infusible ; and if reduced powder, it merely agglutinates a little.' In a small glass tube, they blacken on the first action of the flame; in the open fire, they become white. The colour of these sahlites is the same as that of the before mentioned, but their lustre is much less, and so soft that they are scratched by the nail; while the other sahlite gives sparks with steel. They occur in carbonate of lime, and are usually penetrated by small veins of galena. The analysis of these sahlites occasioned much trouble in ascertaining their true nature. One of the purest specimens is in the collection of Prof. Berzelius, who was kind enough to supply as much of it as was sufficient for a chemical analysis. This sahlite, after having been deprived by diluted nitric acid of calcareous spar, lost on heating in different experiments 4:15, 4:92, 4:34, and 4:11 per cent. which distinguishes it sufficiently from the common malacolite, of which the loss in the fire never amounts to one The powder, after being heated, had a brown-red colour, and gave the following results: pora whic I befor aflu of su sulp! rated a befor blowy per cent.* phate Its 01 iated a * The hard sahlite lost in the fire 0.48 per cent ; the first variety of the malacolite from Bjormyresoeden only 0:12; the second 0:22; and the heden bergite 0-7. This latter mineral when heated in a small glass tube by the lamp of the glass blowers, gives out a sour liquid which seems to contain fuoric acid. it can sahlit hast was ( W mall bu peen fila 2016 Silica. 63.21 containing oxygen 31:79 1.45 10.16 0.99 Oxide of manganese .. 0.82 99.83 prutal chose a 2 other a It is clear that a great surplus of silica exists in this mineral, and that it is not a bisilicate. This exception to the common rule which existed in every other analysis was unexpected. M. Rose repeated the analysis twice, but always obtained the. same result. Fragments of it, when distilled in a small appara tus, gave out water, which did not change any of the test papers. M. Rose endeavoured to find fluoric acid in this sahlite by melting it with carbonate of soda, dissolving the mass in water, evaporating the liquid to a small bulk, separating it from the silica, supersaturating it with muriatic acid, mixing it with excess of ammonia, and adding-muriate of lime, after which the vessel was carefully closed. No precipitate of fluate of lime appeared, not even after several days; and only a trace of silica was deposited. A considerable quantity of another sahlite was distilled in a porcelain retort; the loss amounted to 3.17 per cent. Water was distilled, and at last fumes passed through the aperture of the receiver, which smelt like a mixture of sulphurous and sulphuretted hydrogen. The water in the receiver was slightly sour; when saturated with ammonia, and slowly evaporated in a stove, it left only a small trace of salt of ammonia, which, when heated, evaporated like muriate of ammonia, and before the blowpipe with silica and soda, gave a brown button. By another distillation, when the receiver was kept very cold, a fluid was obtained, which, in the beginning, was turbid, smelt of sulphur, and on being saturated with ammonia, visible traces of sulphur were thrown down. When the sulphur had been separated, this solution was evaporated; the same salt remained as before, the brown colour which it communicated before the blowpipe to the glass of silica and soda, proved to be sulphate of ammonia. This sulphurous acid evidently derives its origin from the sulphuret of lead which occurs disseminated in the sahlite. The very insignificant quantity shows that it cannot be the produce of one of the constituent parts of the sahlite (the water of a perfectly pure sahlite, of which the analysis has been communicated above, did not contain any trace of it). Besides the sulphurous smell, an empyreumatic one was observed in the water, which is peculiar to the water When the liquid which had been separated from the silica was evaporated to a small bulk, and a mixture of sulphuric acid and alcohol poured on it, it burned with a green flame, which, however, depended upon the muriatic ether, and not on boracic obtained from all magnesian minerals, as, for example, serpentine. It was, however, necessary to ascertain, 'whether the whole loss in the fire consisted of water. A quantity of another specimen was, therefore, distilled, which, in different experiments, had lost 3.09, 2.99, and 3.25 per cent. on a red heat, in a porcelain retort with a receiver, to which was adapted a tube with muriate of lime. This experiment, which was made with the greatest care, was decisive, for no gas was given out, and the loss of weight of the retort answered completely to the increase of the receiver, and the tube with muriate of lime.* Fragments of the specimen which had served for this experi- 58:08 containing oxygen 29-21 3.16 8.62 5.30 Alumina 0.47 nese 1.20 97:37 Silica. 58-30 containing oxygen 29.32 2.78 9-37 0.96 . 97.44 If 3.11 per cent. of water are added, which is the mean quantity of the loss that the mineral sustained by a red heat, a small increase is obtained in the analysis. Though the oxygen in the surplus of silica is equal to that of the water obtained, and it, therefore, might appear proper to consider the hydrate of silica as isomorphous with the form of the pyroxene; yet no true hydrate of silica being either found in nature, or produced by art, there exists no reason why it should occur here. It seems as if the distinguishing property of those sahlites, which, on being exposed to heat in a covered vessel, become black, give out water, * The quantity of purified sahlite which was used in this experiment weighed 35.916 grammes. The retort had lost 1.168 grammes ; the gained 1:151, 4 and the tube with muriate of lime 1•009 gramme. and are afterwards white, and which are not fusible, or whose fusi, Prof. Berzelius. 50.00 containing oxygen 25.15 5.62 1.74 4.29 0.66 0.90 pese 97.25 and e of true Jan. 23.-The reading of Mr. Macdonald's Observations on Magnetism was resumed and concluded. The principal subjects of them were the phænomena of the variation of the needle, to account for which, an hypothesis, in some respects new, was proposed by the author. It would appear, he observed, from Capt. Parry's discovery of the north-west magnetic pole, and eing ter -96 and * M. Rose distinctly found afterwards, on closer examination, in one specimen of these sahlites, serpentine mixed with it, which, from its exterior, hardly would have been distinguishable from the sahlite, had he not supposed it to exist in the mixture. |