composition of diamonds. With the great lens of Tschirnhausen
belonging to the Academy he succeeded in burning up several
diamonds, regardless of expense, which, thanks to his
inheritance, he could ignore. In this process he found that a gas
was given off which precipitated lime from water, and proved to
be carbonic acid. Observing this, and experimenting with other
substances known to give off carbonic acid in the same manner, he
was evidently impressed with the now well-known fact that diamond
and charcoal are chemically the same. But if he did really
believe it, he was cautious in expressing his belief fully. "We
should never have expected," he says, "to find any relation
between charcoal and diamond, and it would be unreasonable to
push this analogy too far; it only exists because both substances
seem to be properly ranged in the class of combustible bodies,
and because they are of all these bodies the most fixed when kept
from contact with air."

As we have seen, Priestley, in 1774, had discovered oxygen, or
"dephlogisticated air." Four years later Lavoisier first
advanced his theory that this element discovered by Priestley was
the universal acidifying or oxygenating principle, which, when
combined with charcoal or carbon, formed carbonic acid; when
combined with sulphur, formed sulphuric (or vitriolic) acid; with
nitrogen, formed nitric acid, etc., and when combined with the
metals formed oxides, or calcides. Furthermore, he postulated the
theory that combustion was not due to any such illusive thing as
"phlogiston," since this did not exist, and it seemed to him that
the phenomena of combustion heretofore attributed to phlogiston
could be explained by the action of the new element oxygen and
heat. This was the final blow to the phlogiston theory, which,