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POPULAR SCIENCE REVIEW. 
But if we go back to the time before Lavoisier and bis 
associates, we find that the system then predominant in 
chemistry was founded almost entirely on the reactions, and 
but to a very small extent on the composition of chemical 
substances. 
Chemists then busied themselves continually with studying 
processes of chemical change ; only they contented themselves 
with qualitative knowledge, and hence their hypotheses were 
for the most part extremely vague and their facts disconnected. 
John Joachim Beecher, born about 1630, seems to have 
been the first to weave together the scattered chemical facts 
and guesses into a consistent general theory, which was sub- 
sequently augmented and defined by Stahl (1660-1734). 
Looking at the wonderful changes produced in substances 
by the action of chemical force, the question arose, what 
happens when a body undergoes chemical change ? and as 
burning or combustion was perhaps the commonest of all 
chemical changes, the question became narrowed, and chemists 
eagerly sought for an answer to the query, ‘ What happens 
when a chemical substance burns P ’ 
In those days natural phenomena were referred to the 
presence of 1 principles ’ or 4 essences ’ in the matter exhibiting 
the phenomena. A new principle was added to the list ; and 
the question was supposed to be solved by saying that com- 
bustible substances are characterized by richness in Phlogiston, 
(Gr. Phlogizo = burn, or inflame), and that when they burn 
they lose this principle, so that the burnt substance, or calx, 
consists of the original substance minus Phlogiston. 
The Phlogisteans seem to have regarded their hypothetical 
principle as a modified form of fire, as fire confined in a 
material substance ; but as they gave no definition of fire, 
beyond saying it was one of the four elements, it was scarcely 
to be expected that they should define Phlogiston. 
By restoring Phlogiston to the burnt substance, said the 
theory, the original matter is regenerated. Some substances, 
e.g., charcoal, are especially rich in Phlogiston, and metallic 
calces may be converted into metals, i.e ., may be unburnt, by 
heating them with charcoal. 
Thus the Phlogisteans regarded the phenomena which they 
studied in a purely qualitative manner : they asked only 
What does this or that substance do under given conditions ? 
not being aware that a full answer to this question can only 
be given, when the other question — How much of some given 
effect is produced by a given quantity of this body under stated 
conditions ? had been answered. 
The introduction and use of the balance carried the day in 
favour of those who opposed Phlogistic views. If a substance 
