52 CHEMISTRY FOR AGRICULTURAL STUDENTS 



two alkali-forming or basic oxides were oxides of metals^ the two 

 acid-forming or acidic oxides were oxides of elements which, 

 not being metallic, may be termed fwn-metals. Similarly, other 

 oxides will be found to be basic or acidic according to the 

 metallic or non-metallic nature of their respective elements. 

 Thus the more important oxides may be classified as follows : — 



Metallic or Basic Oxides. 



Oxide of aluminium (alumina). Oxide of magnesium (magnesia). 



Oxide of barium (baryta). Oxide of manganese. 



Oxide of calcium (lime). Oxide of mercury. 



Oxide of copper. Oxide of potassium (potash). 



Oxide of iron. Oxide of sodium (soda). 



Oxide of lead (litharge). Oxide of zinc. 



Non-metallic or Acidic Oxides. 



Oxide of carbon (carbonic acid gas). Oxide of phosphorus (phosphoric 



anhydride). * 

 Oxide of chlorine (hypochlorous Oxide of silicon (silica). 



anhydride).* 

 Oxide ofnitrogen (nitric anhydride).* Oxide of sulphur (sulphurous an- 

 hydride). * 



For the next inquiry use the same solutions of the oxides of 

 potassium, phosphorus, and sulphur, but replace the magnesia 

 by solution of lime, that oxide being more soluble in water. 

 Take the solutions of potash and oxide of sulphur. Note the 

 greasy feel of the one and the sulphurous smell of the other. 

 Pour the one into a portion of the other, frequently stirring and 

 testing the acidity or alkalinity by transferring a drop by means 

 of a glass rod on to a piece of red or blue litmus paper, until 

 the mixture is exactly neutral and has no action on either red 

 or blue litmus. Note that the liquid has lost all greasy feeling 

 and sulphurous smell. Evaporate it to dryness on a water 

 bath, and note the crystalline residue or salt^ a substance 



* So called because of their relation to the corresponding acids. Nitric 

 anhydride is nitric acid without water. 



