1 6 SCIENTIFIC AGRICULTURE. 



20. Oxygen is an invisible gas without taste or 

 smell. It is called a supporter of combustion because 

 wood, coal, oil, gas, and other substances burn in it. 

 If the oxygen be pure they burn with great brilliancy. 

 Combustion, such as takes place in our fireplaces, 

 stoves, and lamps, is the result of chemical union be- 

 tween the oxygen of the air and the carbon and hy- 

 drogen of the fuel. The bright sparks that fly from 

 the blacksmith's anvil are particles of iron uniting 

 with oxygen. 



21. Oxygen unites to form compounds with all. 

 the known elements except fluorine. These com- 

 pounds are called oxides. The compounds of oxy- 

 gen with some of the metals were originally named 

 by merely changing the termination um or him of 

 the metal into a. These names are still in common 

 use. Thus : 



Potassium hydroxide is often called potassa or potash. 

 Sodium hydroxide " soda. 



Magnesium oxide " magnesia. 



Aluminium oxide " alumina. 



Calcium with oxygen forms lime ; silicon forms 

 silica or pure white sand. According to the new. 

 system of naming oxides, the name of the metal 

 comes first with the word oxide immediately after. 



22. Oxygen sometimes unites slowly and gradu- 

 ally with other elements without producing light or 

 intense heat, as when wood decays or iron rusts. 

 These are cases of oxidation, and the final results 





