40 CHEMISTRY OF SOIL. 



The unmetallic are : Tlie metallic are; 



1. Oxygen, 1. Potassium. 



2. Hydrogen. 2. Sodium. 



3. Silicon. 3. Calcium. 



4. Carbon. 4. Magnesium. 



5. Sulphur. 5. Aluminium. 



6. Phosphorus. 6. Ferrum. 



7. Manganesium. 



Restricting the term metalloids to the 3d, 4th, 5th and 

 6th unmetallic substances in the above list, the other two 

 stand out distinctly, separated by their want of properties 

 common to the remainder. They stand each alone, being 

 wholly unlike each other. These are oxygen and hydrogen, 

 known in their uncombined or free state only as gases, whose 

 union produces water. It is as a part of water that hydrogen 

 enters into the composition of rocks. It is comparatively of 

 little importance. 



Not so with oxygen. No other known substance has such 

 a wide range of affinities. Its combinations produce a 

 change of properties in the several elements above enumer- 

 ated, whose names end in um, by which these are converted 

 into substances whose common name reveals their well- 

 known characters. 



41. With the metalloids, oxygen forms acids, and with 

 the metals, oxides or earths, rarely acids. 

 OXYGEN, 



lime, magnesia, are termed alkaline bases; the others, 

 metallic bases. Acids and bases unite and form salts in 



