2dly. The remainder of the metallic arsenic coated the bottom of the inferior large crucible.

3dly. On the sides of the upper crucible or dome were several small globules of gold. And,

4thly. The button of gold in the small crucible, although unchanged in external appearance, was found to be extremely brittle, and, when broken, the fracture appeared of a coarse grain, and of a gray colour.

The button weighed 481,5 grs. so that, exclusive of the gold which had been volatilized, there was an increase of the original weight, amounting to 1,5 gr.

When arsenic is by any means combined with gold, it is not easy to separate it totally by mere heat; for, although this button was twice kept in strong fusion, during one hour each time, in an open crucible, it still retained some arsenic, and continued to be brittle.

From this last experiment it is evident, that a considerable degree of affinity prevails between gold and arsenic ; but, as the latter is immediately volatilized at the instant of contact with melted gold, it cannot easily be combined with it when open vessels are employed, and when the arsenic is simply added to the gold in fusion, while so great a degree of heat is continued.

This volatility of arsenic is, on the contrary, in favour of the combination when the operation is performed in close vessels; for, as arsenic is reduced to a state of vapour by heat much inferior to that which is requisite to the fusion of gold, and as this vapour remains included during the melting and cooling of. the gold, it necessarily follows, that the gold is cooled, and becomes solid, while immersed in the arsenical atmosphere, so that the state of the gold, the extreme division of the arsenic,

and the gradual cooling of the vessels, in every way promote the union of the two metals.

ADDITIONAL EXPERIMENTS UPON GOLD AND ARSENIC.

Since the above experiments were written, I was induced to examine what effects would be produced by arsenic, in the state of vapour, upon red-hot plates of standard gold, the alloy of which was copper.

With the assistance of Mr. BINGLEY, I therefore made the following experiments.

I.

I 30

Two six-inch crucibles were ground so as to fit close when the mouth of one was inverted upon the other. Within the upper crucible or dome, a plate of the standard gold, which was 2 inches long, 1 broad, and thick, and slightly bent, was suspended by a strong iron wire; and one ounce of metallic arsenic was put into the lower crucible. The vessels were then closely luted, and were placed in an open fire, so that they became of a full red heat; they were kept in this state about 12 or 15 minutes, after which, they were removed from the fire, and when cold were opened.

I then found, that although the heat had been so very much inferior to that which is requisite to cause the fusion of gold, yet, in the present case, some very extraordinary effects had been produced; for the arsenic, which had been resolved into vapour, had acted upon the red hot plate of gold, and had combined with every part of its surface; but the combination so formed, being extremely fusible, had immediately separated from the remaining plate of metal, and had fallen into the lower crucible, where it had formed an ingot or button. This ingot

was internally of a gray colour,* and was extremely brittle; but the plate from which the portion of gold had been separated, remained perfectly ductile, and did not retain any of the arsenic ; for, although it was superficially discoloured, it was unchanged in.every other respect, excepting that the sharpness of its edges was destroyed, and the thickness was reduced from of an inch to that of common writing paper.

The effects produced by the arsenic, in this experiment, were very remarkable; for the plate was as uniformly and evenly reduced in its thickness as if it had been planed; and, while the portion which had dropped from it was combined with a very large quantity of arsenic, the remaining part of the plate appeared to have preserved the whole of its original ductility and purity.

These singular effects took place, as I have already observed, in so short a time as 12 or 15 minutes; but I wished to ascertain whether the same would not happen, more or less, within a smaller period, and under circumstances not so favourable to the union of arsenic with gold.

II.

Two six-inch crucibles were fitted, and inverted in the manner already described, and a plate of the standard gold, similar in size and quality to that which had been employed in the first experiment, was in like manner suspended within the upper crucible or dome.

A semicircular piece was cut out of the lip of this crucible, so that, when inverted and luted upon the lower vessel, there was an aperture of about 1 inch in diameter, which was

• The external colour was like that of fine gold, in consequence of the arsenic having been volatilized from the surface of the ingot, by the heat of the lower crucible.

loosely stopped with a piece of charcoal, and the crucibles, being firmly luted, were as before placed in an open fire.

When the vessels appeared of a full red heat, they were taken out, and, being placed upon the pavement of the laboratory, about half an ounce of metallic arsenic was quickly introduced through the aperture that has been mentioned, which was again closed, although very imperfectly, by a piece of charcoal. The arsenic immediately began to produce flame and fumes, which partially escaped through the opening; in about five minutes, the crucibles ceased to appear red-hot, and the greater part of the arsenic was dissipated.

Upon separating the crucibles, the plate of gold was found entire, but it was much discoloured; and the portion of gold which had combined with the arsenic, had trickled to the edges of the plate, where it became accumulated, and would soon have dropped into the lower crucible, had it not been for the short duration of the heat.

The plates of gold which were employed in the two experiments, had been annealed, and were remarkably ductile; and it has already been observed, that the part of the plate which remained after the first experiment, completely retained its original ductility; but the plate which had been employed in the second experiment, although not brittle, was become less flexible. The cause of this difference was very apparent; for, in the first experiment, the whole of the gold combined with arsenic had, by the continuance of the heat, been enabled to flow from the remaining part of the plate of standard gold, which, although thus reduced in size, retained none of the arsenic.

In the second experiment, on the contrary, the heat ceased,

almost as soon as a portion of the arsenic had united with the gold; and the whole surface of the plate, therefore, remained thinly coated with arsenicated gold, by which, a certain degree of rigidity was produced.

These experiments prove, that arsenic, in the state of vapour, will readily combine with gold, even when the latter is only raised to a common red heat. But the whole substance of the gold is not, in this case, immediately and completely pervaded by the arsenic; for it appears, that the combination of these two metals, being extremely fusible, immediately flows, and is separated from the remaining part of the mass of gold, provided that the original degree of heat be not very speedily checked; but, when this happens, the mass or plate of gold remains coated with the arsenicated compound.

The effects which (according to these experiments) metallic arsenic appears to produce upon gold in a red heat, may in a great measure be compared to those which are observed when sulphur, or phosphorus, is combined with various metallic substances.

GOLD ALLOYED WITH ANTIMONY.

Experiment 1.

To eleven ounces one pennyweight and three grains of gold, 23 car. 3grs. fine, in perfect fusion, eighteen pennyweights and twenty-one grains of pure antimony were added, and, being well mixed, the whole was poured into a mould of iron.

This mixture had in some degree acted upon the surface of the mould; for it was with difficulty that the bar could be