92._] Basil Valentine, who was one of the greatest alchemists of the 16th century, discovered many of the properties of the metal antimony, and prepared and examined many compounds of that metal; he made green vitriol from pyrites, brandy from fermented grape-juice, fulminating gold, sulphide of potash, and spirits of salt; he made and used baths of artificial mineral waters, and he prepared various metals by what are now called _wet methods_, for instance, copper, by immersing plates of iron in solutions of bluestone.

He examined the air of mines, and suggested practical methods for determining whether the air in a mine was respirable.

Hoefer draws attention to a remarkable observation recorded by this alchemist.

Speaking of the "spirit of mercury," Basil Valentine says it is "the origin of all the metals; that spirit is nothing else than an air flying here and there without wings; it is a moving wind, which, after it has been chased from its home of Vulcan (that is, fire), returns to the chaos; then it expands and passes into the region of the air from whence it had come." As Hoefer remarks, this is perhaps one of the earliest accounts of the gas discovered by Priestley and studied by Lavoisier, the gas we now call oxygen, and recognise as of paramount importance in chemical reactions.
[Illustration: FIG.XII._See p.

92._] Besides discovering and recording many facts which have become part and parcel of the science of chemistry, the alchemists invented and used various pieces of apparatus, and conducted many operations, which are still employed in chemical laboratories.