THE NATURE OF CHEMICAL PHENOMENA. 
275 
The theory of phlogiston failed to take count of the fact 
that often the calx left after combustion is of greater weight 
than the body burnt, a circumstance quite inconsistent with 
the explanation of the phenomena which this theory offers. 
HoweTer, although Boyle in his “ New Experiments to make the 
parts of Fire and Flame stable and ponderable,” published in 1 673, 
had shown that an increase of weight does frequently occur, and 
had also observed that closed vessels would often break when a 
metal was calcined in them, in consequence of the rarefaction of 
the air, these facts were quite lost sight of, and the theory 
flourished exceedingly until 1772, when Lavoisier turned his 
attention to the subject. This chemist, by numerous experiments, 
established the fundamental principle of modern chemistry that 
matter during the numerous transformations through which it 
passes never undergoes any loss of weight, and, further, aided by 
Priestley’s discovery of oxygen, 1774, shewed that combustion 
in ordinary cases consists in the combination of the body burnt 
with a constituent of the air (oxygen), the weight of the 
products of combustion being exactly equal to the sum of the 
weights of the body burnt, and of the oxygen with which it had 
combined. This, of course, soon put an end to the phlogistic 
theory in its original form. 
The idea of classifying known substances into compounds 
and elements, according as they could or could not be split 
up into two or more substances with distinct properties, had 
been grasped long before the time of Lavoisier by Boyle, but it 
will readily be understood that so long as the theory of 
phlogiston held the minds of chemists, this principle of classi- 
fication was under a great disadvantage. The discoveries 
of Lavoisier, leading as they soon did to a more correct know- 
ledge of the nature of many compounds before misunderstood, 
made its application more precise and complete. 
Thus, about a century since, the fact of the indestructi- 
