FOURTH CHAPTER. 



OXYGEN AND HOW IT ACTS. 



T N THE foregoing chapter we have seen the great 

 influence wielded by the elementary body, 

 oxygen upon carbon. It transformed the solid sub- 

 stance into the gaseous and soluble carbonic acid, 

 thus fitting the carbon for plant food. We have 

 also observ^ed how the oxygen unites with the gas- 

 eous, combustible hydrogen, and condenses with it 

 to the common liquid, water. 



This oxygen is a wonderful element, combining 

 with every other substance, in violent or slow com- 

 bustion, forming gaseous compounds with some sub- 

 stances (as carbonic acid with carbon), liquids with 

 others (as water with hydrogen), and solids with 

 still others (as caustic or fresh-burned lime with the 

 metal calcium). As a product of its combination 

 with hydrogen, we have the harmless compound, 

 water; with carbon, the poisonous gas, carbonic acid; 



with calcium, the corrosive alkali, 

 CompfundB. " caustic lime." As products of its 



combination with other substances we 

 have potash, magnesia, silica, sulphuric acid, phos- 

 phoric acid, etc. Some of these are alkalies, others 

 acids. The former have an acrid taste, the latter a 

 sour taste, and all are corrosive, until neutralized 



