PROPERTIES OF ELEMENTS OF SOIL. 39 



oxygen. Thus are formed sulphuric, carbonic, phos- 

 phoric, silicic acids. (53) 



66. While the metals, combine with oxygen only 

 in one proportion, to form alkalies, producing it al- 

 ways, for each, of one uniform strength, the urets 

 combine with different proportions, and form acids 

 of different strength. The rule followed in nam- 

 ing the acids, is, first, that each is called after the 

 substance forming it, the uret having ous added 

 to it to designate the weaker, and ic, to designate the 

 stronger acid ; thus, 



Sulphur 16+ oxygen 8 is sulphurous acid. 

 " 16+ " 24 is sulphuric acid. 



So are formed also phosphorous and phosphoric 

 acids. Silicon forms but one acid, the silicic. It is 

 the only member of the class urets, which requires 

 a detailed notice of its properties. 



67. Silicon, the base of the earth usually called 

 silex or silica, forms, next to oxygen, the largest part 

 of all rocks and soil. It has been already noticed, 

 (64) how the earthy character, gradually increased 

 from potash to alumina ; and how this last, connect- 

 ed itself with the urets, and in the first member of 

 this series, the earthy character appears fully devel- 

 oped. It is the earth of flints, it is pure rock crys- 

 tal, it is common quartz, agate, and calcedony, and 



