d phlogiston. The definiteness of the statement that a metal,
for example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist that
"metals are produced by the spiritual action of the three principles,
salt, mercury, sulphur"--particularly when it is explained that salt,
mercury, and sulphur were really not what their names implied, and that
there was no universally accepted belief as to what they really were.

The metals, which are now regarded as elementary bodies, were considered
compounds by the phlogistians, and they believed that the calcining of
a metal was a process of simplification. They noted, however, that the
remains of calcination weighed more than the original product, and the
natural inference from this would be that the metal must have taken in
some substance rather than have given off anything. But the phlogistians
had not learned the all-important significance of weights, and their
explanation of variation in weight was either that such gain or loss
was an unimportant "accident" at best, or that phlogiston, being light,
tended to lighten any substance containing it, so that driving it out of
the metal by calcination naturally left the residue heavier.

At first the phlogiston theory seemed to explain in an indisputable way
all the known chemical phenomena. Gradually, however, as experiments
multiplied, it became evident that the plain theory as stated by Stahl
and his followers failed to explain satisfactorily certain laboratory
reactions. To meet these new conditions, certain modifications were
introduced from time to time, giving the theory a flexibility that
would allow it to cover all cases. But as the number of inexplicable
experiments continued to increase, and new modifications to the theory
became necessary, it was found that some of these modifications were
directly contradictory to others, and thus the simple theory became
too cumbersome from the number of its modifications. Its supporters
disagreed among themselves, first as to the explanation of certain
phenomena that did not seem to accord with the phlogistic theory, and
a little later as to the theory itself. But as yet there was no
satisfactory substitute for this theory, which, even if unsatisfactory,
seemed better than anything that had gone before or could be suggested.

But the good effects of the era of experimental research, to which the
theory of Stahl had given s