COMBINATIONS OF OXYGEN. 23 



power iii its combinations. It combines with every other 

 substance and produces the most diverse and opposite com- 

 pounds. With some substances it forms gases, with others 

 liquids or solids; with some it forms acids of the most cor- 

 rosive quality ; with others it forms alkalies equally corro- 

 sive; while a union of two of these an acid and an alkali 

 often forms neutral compounds perfectly bland and in- 

 noxious. An instance may be given. With sulphur, oxygen 

 forms sulphuric acid, the intensely burning and destructive 

 "oil of vitriol" as it is commonly called. With calcium a 

 metal it forms caustic lime, an intensely acrid and de- 

 structive alkali, which corrodes and destroys all vegetable 

 and animal substance. These two combined form sulphate 

 of lime, the well known gypsum, an inoffensive and useful 

 compound well known as "plaster" to every farmer. 



The oxygen of the air is equally diffused through it in 

 the form of a mixture, and not combined. If this oxygen 

 were to become combined with the other element of the air, 

 all life, of whatever kind it might be, would be destroyed 

 in an instant ; for the product of the combination would be 

 that most corrosive substance nitric acid ; but as it is only 

 ihixed it exerts only a beneficent action in supporting life. 

 All combustion is the result of the action of oxygen, it has 

 a powerful affinity for carbon and the other elements of which 

 fuel is composed and unites with them so violently as to 

 produce the heat and light of our fires and lamps. Com- 

 bustible substances bum with greatly increased heat and 

 brilliance in pure oxygen, and the reason why a furnace 

 that is supplied with a blast is so intensely hot, is because a 

 large.volumn of oxygen is forced into it with the increased 

 supply of air. Iron and steel burn with wonderful bril- 

 liancy in a jar of oxygen, if tipped with sulphur, and ignited 

 to start the combustion. This combustion is called oxida- 

 tion and it goes on slowly in the absence of heat ; but is al- 

 ways accompanied by some slight rise of temperature. A 

 piece of iron which slowly oxidizes, or rusts away, to a 

 brown powder which is oxide of iron is subjected to pre- 

 cisely the same amount of heat in the aggregate, as if burn- 



