42 Chemistry. [Lecture 25. 



It is usually in the state of gas that oxygen 

 enters into combination with these matters. 

 Combustion is generally the result of this union ; 

 for as in most of these cases the oxygen gas is 

 condensed, the caloric which retained it in the 

 gaseous state is set free, and the evolution of heat 

 and flame takes place. 



To effect this union, the combustible bodies 

 must be reduced to their ultimate or minutest 

 particles. This is done by the application of 

 heat, which also expands or removes the par- 

 ticles further from the sphere of each other's at- 

 traction, whence their union with oxygen gas is 

 facilitated. Hence flame has been called ignited 

 vapour; that is, it is the combustible body re- 

 duced to the form of vapour, and in that state 

 combining with oxygen gas. 



But one of the most extraordinary and impor- 

 tant properties of oxygen is, that from which it 

 derives its name. Oxus, in Greek, means sharp 

 or acid ; this substance, therefore, having been 

 considered as that which imparts the acid cha- 

 racter to those bodies which are denominated 

 acids, was called oxygen. Thus sulphur in its 

 primitive state is one of the mildest substances in 

 nature, but in combination with oxygen it forms 

 that corrosive and dangerous fluid called sul- 

 phuric acid, formerly oil or spirit of vitriol. 

 It is not, however, to every substance that oxy- 

 gen imparts the acid character; for instance, 

 with hydrogen it forms only water, which has 

 none of the properties of an acid. The only 



