I.—ARGENTIFEROUS GOLD FOIL. (No. 542.)
No. 542.
A piece of Argentiferous
Gold Foil.
Sepulchre IV. Actual size.
The whole of the specimen weighed 2·177 grains, and its thickness varied from 1-500th to 1-600th of an inch. It was one of those gold leaves which were found strewn in vast numbers about the bodies. It was much crumpled, of a reddish yellow colour, and both surfaces appeared as if they had been varnished or lacquered. A sketch of the specimen is annexed of the actual size. By heating, the metal becomes much paler in colour and assumes a greenish yellow tinge, a volatile substance, probably organic, being given off at the same time. The colour of the metal is not affected by digestion in warm alcohol, ether, or benzole; but by boiling it in a strong aqueous solution of caustic potash, it loses its red tinge, and becomes paler, though not so pale as when heated. 1·168 grain of the metal, by cleaning with warm water, dilute hydrochloric acid, and finally gentle rubbing, lost 0·015 grain, which is equal to a loss of 1·28 per cent. The 1·153 grain of cleaned metal was submitted to analysis, with the following results:—
ARGENTIFEROUS GOLD FOIL COMPOSITION PER CENT.
| Gold | 73·11 |
| Silver | 23·37 |
| Copper | 2·22 |
| Lead | 0·35 |
| Iron | 0·24 |
| 99·29 |
From the composition of the specimen it may be inferred that it was an artificial alloy, as the amount of copper and lead present is, so far as we know, much larger than has ever been found in "native gold" from any locality. The presence of the lead is probably owing to the fact of the silver used in preparing the alloy having been refined, though imperfectly, by means of lead. The large proportion of silver present may have been used to economise the gold. An alloy composed of 75 per cent. of gold and 25 per cent. of silver has a distinct gold-yellow colour; but when the silver amounts to 33·33 per cent. the alloy is much paler in colour, and alloys containing more than about that proportion of silver would cease to be designated as gold; the presence of copper would tend to counteract the paleness imparted by silver to gold.
The alteration in colour produced by heating the metal may possibly be due not only to the removal of a coating of organic matter from its surface, but also to the following action. It is well known that an alloy of silver and gold, which contains so much of the former metal as to resemble it in colour, may be made to acquire the colour of gold by superficially removing the silver. This may be effected by various processes, some of which, there is reason to believe, were known to the ancients. When such alloys of silver and gold as those above mentioned are heated to redness for a certain time, after having acquired superficially the colour of gold by any of the processes in question, they resume their original silvery colour. The large oval medal-like coins of the Japanese furnish an excellent illustration of this fact. Such a coin has been found in the Laboratory of the Royal School of Mines to consist of about two parts by weight of silver, and one part of gold. On heating such an alloy sufficiently, it becomes almost silver-white; and on subsequently treating it with hot sulphuric acid the original golden colour is restored.