174) CHEMISTRY. 



The Acidifying Principle. 



Oxygen was raised by Lavoisier to a high rank 

 among chemical substances. He considered it as 

 the acidifying principle, as the only supporter of 

 combustion, and capable of uniting with and modify- 

 ing all other simple bodies. Modern discoveries, 

 however, have considerably lowered the importance 

 of oxygen. 



Sir Humphrey Davy has shown, that it forms alka- 

 lies as well as acids, and that many acids exist which 

 contain no oxygen, yet they perform all the functions 

 of acids. It is consequently not the acidifying prin- 

 ciple, although that doctrine was always maintained 

 by Berthollet. Oxygen has also lost its character 

 of being the only simple supporter of combustion, 

 for chlorine likewise possesses that property, and 

 perhaps in a higher degree than oxygen, with this 

 curious exception, that charcoal will not burn in it, 

 or unite with it. 



The Principle of Combustion. 



After the discovery of oxygen gas, it was adopted 

 by Lavoisier as the only supporter of combustion. 

 The basis of the gas was supposed to unite with the 

 combustible, and the heat and light which it before 

 contained in the gazeous state were said to be evolved 

 in the form of flame. But in this case several requi- 

 sites are not fulfilled. 



The light depends on the combustible, and not on 

 the quantity of oxygen consumed; besides which, 

 there are very numerous instances of combustion in 

 which the oxygen, instead of being solidified, becomes 

 gazeous during the operation; and lastly, in other 

 instances no oxygen whatever is present. 



Combustion, therefore, cannot be considered as 



