lver
and tarnished so as to resemble lead or some base metal. When this was
thrown into acid the coating was removed by chemical action, leaving the
shining metal in the bottom of the vessel. In order to perform some
of these tricks, it is obvious that the alchemist must have been well
supplied with gold, as some of them, when performing before a royal
audience, gave the products to their visitors. But it was always
a paying investment, for once his reputation was established the
gold-maker found an endless variety of ways of turning his alleged
knowledge to account, frequently amassing great wealth.

Some of the cleverest of the charlatans often invited royal or other
distinguished guests to bring with them iron nails to be turned into
gold ones. They were transmuted in the alchemist's crucible before the
eyes of the visitors, the juggler adroitly extracting the iron nail
and inserting a gold one without detection. It mattered little if the
converted gold nail differed in size and shape from the original, for
this change in shape could be laid to the process of transmutation;
and even the very critical were hardly likely to find fault with the
exchange thus made. Furthermore, it was believed that gold possessed the
property of changing its bulk under certain conditions, some of the
more conservative alchemists maintaining that gold was only increased in
bulk, not necessarily created, by certain forms of the magic stone. Thus
a very proficient operator was thought to be able to increase a grain
of gold into a pound of pure metal, while one less expert could only
double, or possibly treble, its original weight.

The actual number of useful discoveries resulting from the efforts of
the alchemists is considerable, some of them of incalculable value.
Roger Bacon, who lived in the thirteenth century, while devoting much
of his time to alchemy, made such valuable discoveries as the theory,
at least, of the telescope, and probably gunpowder. Of this latter
we cannot be sure that the discovery was his own and that he had not
learned of it through the source of old manuscripts. But it is not
impossible nor improbable that he may have hit upon the mixture that
makes the explosives while searching for the philosopher's stone in his
laboratory. "Von Helmont, in the same pursuit, discovered the properties
of gas," says Mackay; "Geber made discoveries in chemistry, which were
equally important; and Paracelsus, amid his perpetual vis