286 OXIDES. 



712. FORMATION OF OXIDES. Oxides 



How are ox- 

 ides formed? may be formed directly by the union of 



Give exam- oxygen and metal, or, indirectly, by sepa- 

 rating them from some salts which con- 

 tain them. Thus oxide of copper may be produced 

 by simply heating copper in the air ; or, by precipita- 

 tion from the nitrate, through the agency of potassa, 

 or, thirdly, by simply heating the nitrate till all the 

 acid is expelled. The oxides of tin and antimony are 

 also directly produced, by the action of nitric acid on 

 the metals. 



What is a hy- 713. HYDRATES, OR HYDRATED OXIDES. 



drated oxide? Oxides commonly combine in the act of 

 precipitation with a certain proportion of water. The 

 compound thus formed, are called hydrated oxides, or 

 simply hydrates. The water may, in most cases, be 

 separated from them by heat, and the uncombined 

 oxide thus obtained. 



714. CONVERSION OF OXIDES. When 



What is said . 



of the conver- oxides are converted into chlorides, sul- 

 sionof oxides? phuretgj ^ by double decompositions, to 



be hereafter described, the chlorides, sulphurets, &c., 

 correspond to the oxides from which they are formed. 

 Thus, protoxide of iron yields protochloride, while ses- 

 quioxide yields sesquichloride. 



715. THE ALKALIES. The oxides of po- 



Give some . 



properties of tassmm and sodium are called alkalies. 

 the alkalies. They are known as pot assa and soda, 



and are commonly obtained as hydrates. They are 

 white infusible substances, from which the water 

 cannot be expelled by heat. They are soluble in water, 



