A HISTORY OF SCIENCE 



This new work when given to the world was not 

 merely an epoch-making book; it was revolutionary. 

 It not only discarded phlogiston altogether, but set 

 forth that metals are simple elements, not compounds 

 of "earth" and "phlogiston." It upheld Cavendish's 

 demonstration that water itself , like air, is a compound 

 of oxygen with another element. In short, it was sci- 

 entific chemistry, in the modern acceptance of the term. 



Lavoisier's observations on combustion are at once 

 important and interesting: "Combustion," he says, 

 " . . . is the decomposition of oxygen produced by a 

 combustible body. The oxygen which forms the base 

 of this gas is absorbed by and enters into combination 

 with the burning body, while the caloric and light 

 are set free. Every combustion necessarily supposes 

 oxygenation; whereas, on the contrary, every oxy- 

 genation does not necessarily imply concomitant com- 

 bustion; because combustion properly so called can- 

 not take place without disengagement of caloric and 

 light. Before combustion can take place, it is necessary 

 that the base of oxygen gas should have greater affinity 

 to the combustible body than it has to caloric ; and this 

 elective attraction, to use Bergman's expression, can 

 only take place at a certain degree of temperature which 

 is different for each combustible substance; hence the 

 necessity of giving the first motion or beginning to 

 every combustion by the approach of a heated body. 

 This necessity of heating any body we mean to burn 

 depends upon certain considerations which have not 

 hitherto been attended to by any natural philosopher, 

 for which reason I shall enlarge a little upon the subject 

 in this place: 



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