1868. | The Past and Present of Chemistry. 25 
attention, vz. :—first, that of enduring the action of fire without 
alteration ; secondly, that of being volatilized by heat, in an un- 
changed condition; and thirdly, that of burning or undergoing 
change by fire. They assumed that an ideal something, which they 
called salt, was the cause of the property of resisting the action of 
fire; that another ideal, something which they termed mercury, was 
the cause of the property of volatility ; and that a third substance, 
also ideal, and named sulphur, was the cause of combustibility. 
And as one at least of these properties occurs in every substance, 
their supposed causes came to be regarded as the constituent ele- 
ments of all matter. If a substance were found to be combustible, 
it contained this ideal sulphur ; if it volatilized without change, the 
ideal mercury was present, whilst if it left an unchanged residue, 
ideal salt was amongst its constituents. 
These so-called elements—sulphur, mercury, and salt—the 
original notion of which may be traced farther back than the 
sixteenth century, played a most important part in the medical 
science of that and the seventeenth century. Physicians then 
believed that the health of the human body, as well as of its 
Separate organs, depended on the combination in certain proportions 
of the before-mentioned elements, that disease was the result of a 
disturbance of these proportions, and that restoration to health was 
effected by their re-establishment. These applications, however, do 
not now immediately concern us, but they are important as in- 
dicating the gradual development of the theory that different 
substances differ, that is, exhibit different qualities, because they 
are composed of different ingredients, or of the same ingredients in 
different proportions ; nevertheless the conception of this idea was 
still so crude that totally dissimilar substances, such as the incom- 
bustible portions of the most widely different bodies were all known 
as the salt constituent, the universally-accepted elements were 
purely fictitious, and that hardly any attempt was made to extract 
them from the substances in which they were supposed to exist. 
But whilst chemists were thus busying themselves with these 
imaginary elements, they were also making gradual progress in the 
sounder recognition of the composition of a great number of sub- 
stances. They discovered, for instance, that copper is present in 
substances which; to the eye, reveal no appearance of metallic 
copper, as in blue vitriol, and that vermillion contains mercury and 
sulphur—not the imaginary elements known by these names—but 
real mercury and real sulphur. Such knowledge as this steadily 
increased and became more prominent. Towards the end of the 
seventeenth century it had in fact made such progress, that the re- 
cognition of the substances which a body may be proved to contain, 
was considered as the only problem which chemistry should strive 
to solve, whilst investigations, involving the assumption of elements, 
