of our author is derived from them.

The third stage of chemistry begins with the fourteenth and ends with
the sixteenth century. It is characterized by an immense growth of
theory, a fertile imagination, and untiring industry. It reached its
height in England about 1440, and is represented by the reputed works
of Lully (vixit circ. 1300), which first appeared about this date. In
this period practical alchemy is on its trial.

The fourth stage begins with Boyle, and closes with the eighteenth
century. Still under the dominion of theoretical alchemy, practical
alchemy was rejected by it, and its interest was concentrated on the
collection of facts. It led up to modern chemistry, which begins with
Lavoisier, and the introduction of the balance in the study of
chemical change.

Chemical theory, then, in our author's time stood somewhat thus.
Metals as regarded their elemental composition were considered to
partake of the nature of earth, water, and air, in various
proportions. Fossils, or those things generated in the earth which
were not metals, were again subdivided into two classes--those which
liquefy on being heated, as sulphur, nitre, etc., and those which do
not. The metals were considered to be composed of sulphur and mercury.
These substances are themselves compounds, but they act as elements in
the composition of metals. Sulphur represented their combustible
aspect, and also that which gave them their solid form; while mercury
was that to which their weight and powers of becoming fluid were due.

This theory was due to two main facts. Most ores of metals, especially
of copper and lead, contain much sulphur, which can be either obtained