the most perfect of all the metals. See Chemistry-Index in this Supplement.

It has been a very common opinion among metallurgists, that tin has the property of destroying the ductility of gold; on being melted with it even in very small quantities; and Dr Lewis adds, that even the vapours which arise from tin in the fire, make gold so brittle, that it flies in pieces under the hammer. This opinion was controverted by Stanefby Alchorne, Esq; of his Majesty's mint, who made a set of experiments, which, in his opinion, authorise a very different conclusion, viz. that though tin, like other inferior metals, will

(a) This name was given to the earth of beryl by the editors of the Annales de Chemi. Its most characteristic property being that it forms salts of a saccharine taste, they gave it a name derived from γλυκος, to render sweet. According to this etymology, should not the name be Glycina? will contaminate gold in proportion to the quantity mixed with it, yet there does not appear in tin any thing specifically inimical to that precious metal.

As we have elsewhere (See Chemistry, no 1091, &c. Encyc.) enumerated these experiments, and admitted the conclusion drawn from them, it becomes our duty, in this place, to state what has been urged against that conclusion.

M. Tillet, being in his own mind persuaded that tin renders gold so brittle that it cannot be reduced to thin leaves, and far less be made to pass through the wire plate but by virtue of repeated annealing, and peculiar treatment, which gold of the usual ductility does not require, determined, from respect to M. Alchorne, to repeat his experiments.

His first experiment consisted in mixing 24 grains of fine gold with one of tin which contained no arsenic. He wrapped the grain of tin in the 24 grains of gold reduced to a very thin leaf, and placed the whole upon a piece of charcoal, so hollowed out as to support the mixed metal during fusion. He even sprinkled a small quantity of calcined borax upon the metal, in order that the fusion might be more sudden, that the metal might flow together, and the tin unite with the gold, without allowing time for it to become calcined. This alloy was speedily fused by the enameller's lamp, and reduced into a small button without any loss of weight. It was then flattened carefully beneath the hammer; but, notwithstanding his utmost precaution in this respect, it cracked, and at last broke into three pieces, its thickness then being a quarter of an line or thereabouts. He repeated this experiment with a double quantity as well of pure gold as of tin, and the result was the same.

He next alloyed 4 ounces of gold, of the fineness of 22 carats, with 1 gros 24 grains of tin deprived of arsenic, or, in other words, with 4 pennyweights of tin; and these two metals being reduced into small pieces, were mixed together, put into a crucible, and urged by the strong heat of a forge with two pair of bellows. When their fusion appeared to be complete, he poured the metal into a small ingot mould proportioned to the quantity.

The ingot thus obtained had lost scarcely anything of the weight of the two metals that composed it; which was a proof that the tin had united and incorporated with the four ounces of gold. But on attempting to bend the ingot, which was about six inches long, and not more than two or three lines thick, he remarked, contrary to the nature of gold of 22 carats, that it was rigid, and would have required a considerable effort to give it any degree of curvature, or bring it to the flexibility it would have possessed if no tin had entered into its composition. Not satisfied, however, with the inference naturally flowing from this circumstance, he proceeded to the proper test by hammering, particularly with the edge of the hammer, in order that the bar might be lengthened, and by that means submitted to the most decisive proof. He did not observe, during the continuation of this process, till the bar was reduced to about two-thirds of its first thickness, that its edges were cracked, or exhibited much of the appearance of brittleness; but as he was apprehensive that this accident might happen by too long hammering, he divided the bar by cutting off the part which had been hammered out. This part was placed in the midst of lighted charcoal, in order that, by a moderate annealing, it might recover the state of malleability it possessed before it was hammered. But when he went to take it out of the fire, where it had undergone no greater heat than a cherry-red, he found it divided into two parts. After having suffered these to cool, he forged them again. They were extended with considerable ease, though with some cracks at the edges; but they did not yet satisfy the whole of his enquiries. He therefore annealed one of the two last mentioned pieces a second time, and referred the other in its hard-hammered state to be passed between the laminating rollers. The annealed part, which might have the thickness of about a shilling, broke in the fire, though the heat was very gentle, into four or five portions. The longest of these portions, which best reflected the action of the fire, bent and twisted itself, and showed, by this state of strong contraction in different directions, that it had tended to break and become divided into small portions, similar to those which had already separated from it.

Satisfied by this experiment that the piece of the mixed ingot which he had kept in its hammer-hardened state would not bear annealing, he determined to extend it still more between the rollers, setting them up very gradually, in order that the fracture, if it should take place, might be principally owing to the brittleness of the material, and not to the force of compression to which it was subjected. By this management he succeeded in extending the metal to double its length notwithstanding its hardness, and rendering it as thin as strong paper; though the edges were cracked through their whole length like the teeth of a saw. But this accident is not at all surprising, when it is considered that gold, though alloyed simply with copper, whatever may be the cause, does not possess its usual ductility, particularly when it is laminated very thin, without repeated annealing as the metal becomes hard.

Aware that the fracture of the pieces of gold might be attributed to an incomplete fusion, or unequal mixture of the two metals, he melted the whole ingot over again with the utmost precaution; but in vain. The metal was as brittle as formerly, and would not bear annealing.

He next fused 6 ounces of pure gold of 24 carats with 2 gros, or 6 penny-weights of tin, taking every possible precaution to have the metals completely mixed. When the whole was in perfect fusion, he poured the mixture into an ingot mould, and obtained an ingot rather longer and cleaner than the two former. As soon as it was cold he forged one of its extremities with the edge of the hammer. It was lengthened without any perceptible crack; and when it was reduced to the thickness of one line, or thereabouts, he cut it off for separate treatment. By moderate annealing it maintained its integrity; and, with the exception of a few cracks, it passed the laminating rollers without breaking. As he was fearful, nevertheless, that it might break in some part if he continued to laminate it, he gave it a slight annealing; it had scarcely acquired a cherry-redness between the charcoal, before it broke into five or six parts, some of which were simply bended or twisted, and others flat as they quitted the rollers. Among the annealed pieces of this extremity of the ingot, there was one sufficiently long, though a little curled, which he laminated a second time, with the determination of rendering it very thin without the least annealing. It acquired at least double the length it had at first without breaking; and, if we except the two sides of this plate which were cracked, the body, or main piece, was entire. It was spongy, and might be considered as if formed out of an ingot of common gold containing no tin, but not possessing the whole of its natural ductility.

"It follows, says M. Tillet, from these experiments, that gold, whether fine or alloyed, when perfectly fused with a small portion of the finest tin, acquires rigidity and hardness by the mixture; that it loses somewhat of its distinguishing colour; and that it may, indeed, by careful management, be extended to a certain degree by the hammer, or still better by the rollers; but that, as it cannot be annealed without danger of breaking, it is by this defect deprived of the essential advantage of recovering its original softness after it has been strongly hammer-hardened. It is not but by careful management in the use of the hammer, and by frequent annealings, that artists employed on works of gold and silver succeed in obtaining them without cracks, and bringing them to a state of perfection, without being obliged to have recourse to solder to repair the defects which excessive hardness under the hammer would occasion. How much, therefore, ought gold-workers, who continually have this metal in their hands, to be attentive to prevent the introduction of tin in their workshops, and never to employ such compounds of gold as are subject to break, or even to warp, while annealing? The expense of refining, which they would pay for deputing such compounds, would be of less consequence to them than the loss of time required for the careful management of such gold contaminated by tin, even if they did succeed in using it, and were not often forced to abandon, after much labour, a work nearly finished.

"If it be allowable (continues our author) to form conjectures on the cause of the fracture of plates of gold containing tin, when subjected to the annealing heat, it may be presumed, since tin very speedily melts, while gold requires a strong heat for its fusion, that the parts of the tin intermixed in a sort of proportional equality with those of the gold, tend to separate by a speedy fusion and at a very gentle degree of heat; that they remain without confluence between the parts of the gold, while the latter preserve the whole of their solidity, and do not lose it even by the annealing heat: whence it seems, that the parts of the precious metal, when ignited among the coals, having no longer the solid connection formed by the tin, but, on the contrary, having an infinite number of small cavities occupied by particles of that metal in fusion, must tend to diffusion; whereas the same accident does not take place in the pieces which have resisted the annealing, and have been laminated after cooling, because the particles of tin have become solid by cooling, and have recovered their original state of union with the gold.

"This fracture of the compound does not take place with an alloy of gold and copper, for an opposite reason to that which has here been explained; namely, because these two metals require nearly the same heat for their fusion. The effect of annealing being there-

fore equal upon both, the metals, notwithstanding this treatment, preserve their natural confluence, even tho' the heat be carried near the point of fusion."

Gold-Leaf. See Gold-Leaves (Encycl.) where a full account is given from Dr Lewis of the process of gold-beating. In that article, we have said that gold-leaf ought to be prepared from the finest gold; but Mr Nicholson, who, in all probability, knows much more of the matter than the author from whom our account was copied, affirms us that this is a mistake, and that pure gold is too ductile to be worked between the gold-beaters' skin. The newest skins will work the finest gold, and make the thinnest leaf, because they are the smoothest. Old skins, being rough or foul, require coarser gold. The finer the gold, the more ductile; infomuch that pure gold, when driven out by the hammer, is too soft to force itself over the irregularities, but would pass round them, and by that means become divided into narrow slips. The finest gold for this purpose has three grains of alloy in the ounce, and the coarsest twelve grains. In general, the alloy is six grains, or one eightieth part. That which is called pale gold contains three pennyweights of silver in the ounce. The alloy of leaf gold is silver, or copper, or both, and the colour is produced of various tints accordingly. Two ounces and two pennyweights of gold is delivered by the master to the workman, who, if extraordinarily skilful, returns two thousand leaves, or eighty books of gold, together with one ounce and five pennyweights of waste cuttings. Hence one book weighs 4.8 grains; and as the leaves measure 3.5 inches in the side, the thickness of the leaf is one two hundred and eighty-two thousandth part of an inch.

The yellow metal called Dutch gold is fine brass. It is said to be made from copperplates, by cementation with calamine, without subsequent fusion. Its thickness, compared with that of leaf gold, proved as 19 to 4; and under equal surfaces it is considerably more than twice as heavy as the gold. Nicholson's Journal, Vol. 177.