Note 156 — MIRRORS135.
William Johnston translation
As the account of these experiments is given only in an expensive work, which may not often fall into the hands of those who are best able to examine it, I insert it here. “The ancient mirror, which I examined, was a metallic mixture, very tender and brittle, and of a whitish colour inclining to grey. When put into the fire, it remained a long time in a state of ignition before it melted. It was neither inflammable nor emitted any smell like garlic, which would have been the case had it contained arsenic. It did not either produce those flowers which are generally produced by all mixtures in which there is zinc. Besides, the basis of this mixture being copper, it would have been of a yellow colour had that semi-metal formed a part of it. I took two drams of it and dissolved them in the nitrous acid. A solution was speedily formed, which assumed the same colour as solutions of copper. It precipitated a white powder, which I carefully edulcorated and dried. Having put it into a crucible with a reductive flux, I obtained lead very soft and malleable.
“Having filtered the solution, I took a part of it, upon which I poured an infusion of gall-nuts, but it produced no change. A solution of gold, which I poured upon another part, made it assume a beautiful green colour; but no precipitate was formed: which is sufficient to prove that there was neither iron nor tin in the mixture.
“On the remaining part of the solution I poured a sufficient quantity of the volatile alkali to dissolve all the copper that might be contained in it. The solution became of a beautiful sapphire blue colour, and a white precipitate was formed. Having decanted the liquor, and carefully edulcorated the precipitate, I endeavoured to reduce it; but whether it was owing to the quantity being too small, or to my not giving it sufficient heat, I could not succeed. I had recourse therefore to another method.
“I took the weight of two drams of the mixture, which I brought to a high state of ignition in a cuppel. When it was of a whitish-red colour, I threw upon it gradually four drams of sulphur, and when the flame ceased, I strengthened the fire in order to bring it to complete fusion. By these means I obtained a tender brittle regulus, whiter than the mixture, in which I observed a few small needles. Being apprehensive that some copper might still remain, I sulphurated it a second time, and then obtained a small regulus which was almost pure antimony.
“It results from these experiments, that the metal of which the ancients made their mirrors was a composition of copper, regulus of antimony, and lead. Copper was the predominant, and lead the smallest part of the mixture; but it is very difficult, as is well known, to determine with any certainty the exact proportion of the substances contained in such compositions.”
[In the examination of an Etruscan mirror, which was placed in my hands for analysis by Professor Gerhardt of Berlin, it was found to consist, in 100 parts, of 67·12 copper, 24·93 tin, and 8·13 lead, approximating closely to an alloy of eight parts of copper to three of tin and one of lead. The oxide of tin obtained in the course of analysis was carefully examined, before the blowpipe, for antimony, but I did not succeed in detecting a trace of that metal. A similar mirror had been likewise analysed by Klaproth; he found 62 per cent. copper, 32 tin, and 6 per cent. lead, but no trace of antimony.—W. F.]