e gases in mines were manifestations of devils, and he
specified two classes--one of malignant imps, who blow out the miners'
lamps, and the other of friendly imps, who simply tease the workmen in
various ways. He went so far as to say that one of these spirits in the
Saxon mine of Annaberg destroyed twelve workmen at once by the power of
his breath.

At the end of the sixteenth century we find a writer on mineralogy
complaining that the mines in France and Germany had been in large part
abandoned on account of the "evil spirits of metals which had taken
possession of them."

Even as late as the seventeenth century, Van Helmont, after he
had broken away from alchemy and opened one of the great paths to
chemistry--even after he had announced to the world the existence of
various gases and the mode of their generation--was not strong enough to
free himself from theologic bias; he still inclined to believe that the
gases he had discovered, were in some sense living spirits, beneficent
or diabolical.

But at various. periods glimpses of the truth had been gained. The
ancient view had not been entirely forgotten; and as far back as the
first part of the thirteenth century Albert the Great suggested a
natural cause in the possibility of exhalations from minerals causing a
"corruption of the air"; but he, as we have seen, was driven or
dragged off into, theological studies, and the world relapsed into the
theological view.

Toward the end of the fifteenth century there had come a great genius
laden with important truths in chemistry, but for whom the world was
not ready--Basil Valentine. His discoveries anticipated much that has
brought fame and fortune to chemists since, yet so fearful of danger was
he that his work was carefully concealed. Not until after his death was
his treatise on alchemy found, and even then it was for a long time not
known where and when he lived. The papal bull, Spondent pariter, and the
various prohibitions it bred, forcing other alchemists to conceal their
laboratories, led him to let himself be known during his life at Erfurt
simply as an apothecary, and to wait until after his death to make a
revelation of truth which during his lifetime might have cost him dear.
Among the legacies of this greatest of the alchemists was the doctrine
that the air which asphyxiates workers in mines is similar to that which
is produced by fermentation of malt, and a recommendation that, in
order to drive away th