The bar thus formed was of a pale yellowish gray, approaching to a dull white; it was very ductile, and, with great ease, was reduced by the rollers from of an inch to the thickness of a guinea. It was then cut without difficulty, by the punches, into blanks, and these were afterwards stamped with great ease, although they had not been annealed.

Experiment 11.

The same bar was again melted, and was cast in a sand mould; it then appeared to be very brittle, but this, it was proved, was occasioned by the effects of the sand mould, which had rendered the metal porous; for, when the parts had been approached by previous hammering, the bar was rolled, and, in every respect, was found to be as ductile as in the former expe

riment.

Experiment 111.

Eighteen pennyweights and ten grains of the fine gold being melted, one pennyweight and fourteen grains of cast-iron nails were added, and, when fused, the whole was cast in a mould of iron.

This metal, in colour, much resembled the former; and was also perfectly ductile.

Experiment iv.

This was the same as Exper. 111. but thin plate cast-steel was employed, instead of cast-iron.

The properties of this metal, in respect to colour, ductility, &c. resembled the former.

Experiment v.

To eighteen pennyweights and ten grains of fine gold, alloyed

with 19 grains of copper, 19 grains of fine iron wire were added, and the mixture was treated as before.

The colour of this metal was pale grayish yellow; it was perfectly ductile, and was rolled and stamped, without being previously annealed.

By these experiments it appears, that gold made standard by wrought and cast iron, and even by cast-steel, is not brittle, as has generally been asserted; for, although gold undoubtedly is thus rendered harder, it nevertheless does not become brittle, but remains so ductile, that it may be hammered, rolled, and stamped, without requiring to be annealed; and, allowing that the change of colour produced by iron upon gold renders it unfit for coin, yet this mixture may probably be employed with advantage in ornamental and other works."

Emery is enumerated by mineralogists among the ores of iron; and many very intelligent assayers, and others, even at this time, believe it to be a frequent cause of the brittleness of gold.

Some eminent metallurgists, such as SCHLUTTER, support the same opinion, and have recommended certain processes to be employed to refine the gold, when thus adulterated. † It must however be allowed, that it is not easy to conceive how such a combination can take place; for if (as is generally believed) emery consists of oxide of iron and siliceous earth, such a substance cannot unite with gold in the metallic state; and, even supposing that the ferruginous ingredient could in any manner be combined with gold, yet it has been fully proved, in another

• It is said that this mixture is sometimes employed by goldsmiths. SCHLUTTER, Docimasie, p. 282.

part of this Paper, that gold does not become brittle by the addition of iron. In order, however, to ascertain what effects could be produced by emery,* the following experiments were made.

EXPERIMENTS ON EMERY AND GOLD.

Experiment 1.

One ounce of fine gold was put into a small crucible, and was completely covered with emery, which had been reduced to a fine powder.

The gold was kept in fusion during one hour, and was frequently stirred, after which, it was poured into a mould.

Not the smallest change, in colour, ductility, or any other property, was thus produced.

Experiment II.

About half an ounce of fine powder of emery was, several times, alternately moistened with olive oil and made red hot, after which, it was put into a crucible lined with charcoal.

• Mr. TENNANT has lately shown, (Phil. Trans. for 1802, page 400,) that emery is composed of alumina, silica, and iron. In one case, he obtained,

And, from another variety, more impregnated with iron, he obtained,

An ounce of fine gold was placed in the middle of the emery; the crucible lined with charcoal was closed by a stopper of the same, and a cover was luted upon the exterior crucible.

After a very strong heat of one hour and a half, the gold was found to be exactly of the same colour, ductility, &c. as before.

Experiment III.

The preceding experiment was repeated; but the heat was continued during three hours, so that at length the crucible began to be melted.

It was suffered to cool in the furnace; and, being afterwards broken, the gold was found crystallized in a reticulated form, but not altered in colour or ductility. The emery was reduced to a dark gray or blackish slag, which occupied the upper part of the crucible.

We have, from the above described experiments, sufficient proof that emery will not combine with gold; and, when the difficulty of uniting metallic oxides in general, or any earthy substance, with a metal, is considered, it appears singular that the existence of such a combination as that of emery with gold should ever have been believed.

It is not however improbable, but that some other substance has been occasionally denoted by the term smiris, emeril, or emery; and Dr. LEWIS appears to be inclined to adopt this opinion.*

GOLD ALLOYED WITH PLATINA.

Experiment 1.

Eighteen pennyweights and ten grains of gold, 23 car. 31 grs.

Phil. Comm. of Arts, p. 607.

fine, being completely melted, one pennyweight and fourteen grains of purified platina were added, and, when well mixed, the whole was poured into a mould.

This metal was of a yellowish white, like tarnished silver, and was extremely ductile.*

The specific gravity of it was 19,013.

Experiment 11.

The ounce of standard gold formed by the foregoing experiment, was again alloyed with one pennyweight and fourteen grains of copper, so that the standard proportion of alloy was doubled.

This metal was of a pale dull yellow; it was not quite so ductile as the former; and the specific gravity was 16,816.

It was not thought necessary to extend these experiments, as the properties and effects of platina upon gold are now so generally known, as well as the means usually employed to detect it.†

• The platina had been purified by precipitation with muriate of ammonia, and was therefore in the state of a fine metallic powder, which probably contributed much to facilitate the union of it with the gold. I must observe, however, that it was not absolutely pure, for it still contained a small portion of iron.

The specific gravity of this platina was 18,717.

Gold made standard by platina, is not only very ductile, but also (when hammered) tolerably elastic. Perhaps it might be advantageously employed for the springs of watches, &c.

+ Quand le platine ne surpasse pas les 30 à 40 millièmes de son alliage avec l'or, ce dernier n'en garde point, si le départ est fait avec les précautions nécessaires; et, lorsque ce métal est au-dessus de ce terme, la fraude devient trop sensible et trop évidente, pour qu'on ne s'en apperçoive pas; imo, par la plus grande chaleur que l'essai demande pour passer et prendre une forme arrondie; 2do, par l'absence de l'éclair; 3mo, par la surface crystallisée, et la couleur blanche et matte du bouton; 4mo, par la couleur jaune de paille, plus ou moins foncée, qu'il communique à l'eau-forte pendant