ARTICLE V.

New Investigation of the Chemical Composition of Red Silver Ore.* By P. A. v. Bonsdorff.

IN consequence of the analysis of red silver ore by Klaproth and Vauquelin, this mineral has been considered as a compound of sulphuret of silver, sulphuret of antimony, and oxide of antimony. Klaproth's last analysis of this mineral from Andreasberg (Beitrage, v. 197) makes its constituents as follows:

But both in this analysis, and in the others made upon the same mineral, although the quantities of constituents obtained were unequal, no positive proof was obtained of the presence of oxygen, or of oxide of antimony. It was merely concluded that the great loss sustained during the analysis was owing to the presence of oxygen. In this way Vauquelin reckoned the whole foss, which was about 12 per cent. as oxygen. And Klaproth, for the same reason, reckoned 4 or 5 per cent. of oxygen in his different analyses. But as the result of these analyses do not agree with any atomic proportions; and as both the existence and amount of the oxygen still depend upon imperfect and uncertain evidence, I was in hopes that a new analysis might not be destitute of all interest. In Prof. Berzelius's laboratory, I lately enjoyed a fortunate opportunity of undertaking the analysis of the dark red silver ore from Andreasberg; and I propose in this paper to give an account of the analytical experiments which I undertook, and of the result of them.

The first attempt was to extract the supposed oxide of antimony from the mineral by means of dilute muriatic acid. Picked specimens of the ore were reduced to the finest possible powder,† and digested with muriatic acid, rendered so weak as not to be able to decompose sulphuret of antimony. This degree of dilution was determined by means of a paper dipped in acetate of lead; but it was found that the acid when thus diluted would dissolve nothing whatever from the mineral.

338.

Translated from the Kongl. Vetenskaps Academiens Handlingar for 1821, p.

+ The pulverisation of this mineral is attended with considerable difficulty, because the parts of it become at last scaly, after which it is far from easy to reduce them to a finer powder, even under water.

The next attempt was to expose the mineral to the action of hydrogen gas, while at the same time heat was applied to it, in hopes that the hydrogen would reduce the oxide of antimony to the metallic state and form water, by the weight of which the quantity of oxygen in the mineral could be determined. But in order to satisfy myself in the first place that this theoretic speculation would accord with the nature of the bodies present, I undertook a set of experiments on the reduction of an artificial mixture of sulphuret and oxide of antimony by means of hydrogen gas.

The apparatus which was employed in these processes was constructed on almost the same idea as that described by Prof. Berzelius in his experiments on nickel glanse, arsenical nickel, &c.; an outline of which is here given.

It consisted of a globular vessel, A, in which the gas was generated, a tube, C, filled with chloride of calcium, and a small apparatus for distilling. But this last apparatus, distinguished in the figure by the letters DEFG H, was, in my experiments, not terminated by the ball, F, and the crooked tube, G H; but had on that side merely a straight tube rather more than two inches long, which was fastened to the ball, E, by a caoutchouc tube in the same way as the apparatus, D E, only somewhat greater. This tube was filled with chloride of calcium in the same way as the tube C, and from A there passed a crooked tube to allow the gas evolved to make its escape. The gas was

generated by dissolving granulated zinc in dilute sulphuric acid. All the different pieces of the apparatus were carefully weighed in the first place to enable me to determine what might be driven off, or what addition might be made to the substances operated on during the process.

Experiments with a Mixture of Sulphuret of Antimony and Oxide of Antimony.

Antimonious acid prepared from subantimonite of potash (crocus antimonii elota) by digestion in nitric acid, was mixed by trituration with its own weight of metallic antimony in fine powder, and put into a glass globular vessel blown by the lamp, having a capacity of fully a cubic inch, the mouth of which was afterwards drawn out into a capillary tube. This glass vessel was put into a crucible, and was raised to a red heat, which was kept up about ten minutes. When the glass was broken in pieces, there was found in its upper part white or yellowish-white crystals, of two different forms; namely, octahedrons and prismatic needles. The mass found at the bottom consisted of a metalline regulus lying undermost, and over it an oxide consisting of a fused yellow-grey mass, having a crystallized fracture, and containing drusy cavities, lined with white, short, needleshaped crystals. Sulphuret of antimony was prepared from this regulus by mixing it with 40 per cent. of pure native sulphur, and heating it in a little glass globular vessel. It was crystallized,, and all excess of sulphur had been driven off by heat.

The purest portions of the oxide thus obtained were pulverised, and exactly mixed with the sulphuret of antimony, accord ing to the proportions which Berzelius has given for the constitution of red ore of antimony (Rothspeissylanserz), Sb + 2 Sb, S3; namely, 100 parts sulphuret with 43-2 parts of oxide. A quantity of this mixture was put into a glass globe blown by the lamp. This quantity after being gently heated weighed 2335 grammes. The glass was exposed to the flame of a spirit-lamp, and as soon as the mixture became fully red-hot, it melted,, and was found after cooling still to weigh exactly 2·335 grammes. The product of this operation was a glass having the metallic lustre and a dark steel-grey colour with a shade of red, very similar to the dark variety of red ore of antimony. It appeared opaque, except those portions which had formed a thin crust on the inside of the glass. These were translucent, and had a yel lowish-red colour. When reduced to powder, it had a dark reddish-brown colour. As the weight was not altered by the fusion, it is obvious that it had lost no sulphur nor oxygen during the process.

A portion of the powder of this crocus, or compound of sulphuret and oxide of antimony, was put into the part of the apparatus marked E, which, after being gently heated, weighed

1.27 gramme. The caoutchouc tube was now fixed on, and all the other parts of the apparatus were adjusted to their places. After the hydrogen gas had passed over a good while, and the whole atmospherical air had been driven out of the tube, the powder was gradually heated by means of a spirit-lamp. Water began very quickly to be formed, and was deposited in the form of vapour on the sides of the glass globe. When the hydrogen gas passed over briskly, the aqueous vapour was carried off by the current, and was naturally absorbed by the chloride of calcium in G; but when the hydrogen gas passed over slowly, or only at intervals, the water collected in drops in the pipe. After the process had continued two or three hours, the antimoniacal mass had in part passed through the glass globe, and a little sulphur began to appear on its outside. The fire was of necessity withdrawn, and the process stopped. During the whole continuance of the operation sulphuretted hydrogen gas was disengaged, and conducted by means of the crooked tube into a glass containing liquid ammonia in order to prevent it from making its way into the room. Into the tube beyond the glass globe, 0.04 gramme of water had condensed, and the tube containing the chloride of calcium had increased considerably in weight. But it is needless to state this increase, because the portion of the chloride nearest the ammoniacal water had deliquesced in consequence of the evaporation of a portion of that liquid into it. The residual matter in E weighed 1.005; and consequently it had lost in oxygen and sulphur 0-265 gr. It consisted of a multitude of small metallic reguli, and of a brassyellow crystallized sublimate, which seemed to have the octahedral form. There was also a little sublimate in the tube, which had more of the metallic lustre, and was more shining, and which probably was merely sulphuret of antimony. The yellow crystallized substance dissolved with ease in aqua regia, and seemed to consist chiefly of sulphur.

Decomposition of Red Silver Ore by Hydrogen Gas.

When it was thus ascertained that hydrogen gas is capable of reducing oxide of antimony from its combination with sulphuret of antimony, the same process was undertaken with red silver ore, and at the same time measures were taken to collect and decompose all the sulphuretted hydrogen formed during the process, that the quantity of sulphur in the ore might be likewise determined. For this purpose a somewhat concentrated solution of sulphate of copper was prepared, and a portion of it (previously deprived of its atmospherical air by boiling) was put into two phials; and another portion supersaturated with ammonia, so that a clear solution was obtained, was put into two other phials. A new portion of chloride of calcium was put into the tube G, and its weight was again determined, and from

it there was a communication by means of glass tubes with the phials holding the solution of sulphate of copper. These again communicated with the ammoniacal solution of copper in the other two phials, by means of glass tubes passing through corks in the mouths of the phials, precisely as in a common set of Woulfe's bottles. Into the glass globe E, a quantity of pulverised red silver ore was put, which, after having been gently heated, weighed 1.504 gramme. Then the whole apparatus was put in its place.

When the evolution of the gas had continued for half an hour, and the atmospherical air had been expelled, a spirit-lamp was applied to the ball E, and a stream of gas was made to pass equably and slowly. On the first application of the heat, a light coloured smoke appeared, and passed over into the pipe from E, but it vanished immediately, and left no trace behind it. Sulphuretted hydrogen gas was immediately formed, and instantly rendered the first phial turbid. Soon after a deposit began to appear in the second, then in the third, and at last even some deposit appeared in the fourth phial. In the ball and tube not the least trace of water made its appearance, and indeed nothing whatever but an exceedingly small quantity of smokelike matter. After the heat had been continued without interruption for eight hours, the mineral had assumed the form of a metallic regulus, which easily melted by the heat of the spiritlamp. And in the throat, and tube of the little apparatus E, an inconsiderable quantity of a greyish matter with the metallic lustre had sublimed. When the hydrogen gas ceased to be sulphureous, and the mineral to diminish any more, the gas was still allowed to pass for some time. The lamp was then put out, and the apparatus taken to pieces. The residue in the retort was found to weigh 1.2365 gr. The glass ball was broken, and the regulus taken out; it weighed 1.2255 gr. It had externally the metallic lustre; but was here and there covered with a little black powder; but its quantity was so small that it could not be separated. Probably it was nothing else than small reguli in very fine mechanical division. The tube beyond the glass ball, though it contained the smoke-like matter, was not sensibly increased in weight. The chloride of calcium had become heavier by 0.010 gr. and it was observed that the particles of salt were a little soiled by a fine brownish-grey matter. The hydrogen had taken from the mineral 1-504 - 1·2365 = 0.2675 gramme, which amounts to 17.785 per cent.

A set of experiments was now undertaken on the regulus, which exhibited all the characters of an alloy of silver and antimony. The object in view was to remove the antimony by cupellation, and leave the silver. But in the first place a set of experiments was made upon an artificial mixture of silver and antimony.

New Series, VOL. VIII.

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