54 PROPERTIES OF ELEMENTS OF SOIL. 



of iron, or iron pyrites, sulphuret of potassium, or liver of 

 sulphur. 



2d. They chemically combine with each other. Thus are 

 formed sulphuret of carbon, and sulphuret of silicon. 



3d. They all form acids, by combining with oxygen. 

 Thus are formed sulphuric, carbonic, phosphoric, silicic 

 acids (41). 



66. While the metals combine with oxygen only in one 

 proportion, to form alkalies, producing it always, for each, 

 of one uniform strength, the metalloids combine with differ- 

 ent proportions, and form acids of different strength. The 

 rule followed in naming the acids, is, first, that each is called 

 after the substance forming it, the metalloid having ous 

 added to it to designate the weaker, and 2c, to designate the 

 stronger acid ; thus : 



Sulphur 16+2 oxygen == 16 is sulphurous acid. 

 " 16 + 3 " =24 is sulphuric acid. 



So are formed phosphorus and phosphoric acids. Silicon 

 forms but one acid, the silicic. It is the only member of its 

 class which requires a detailed notice of its properties. 



Q7. 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 connected itself with the metalloids, and in the 

 first member of this series, the earthy character appears 

 fully developed when united with oxygen. It is the earth 

 of flints, it is pure rock crystal, it is common quartz, agate, 

 and calcedony, and cornelian. All these are silicon acidified 

 by oxygen, hence called silicic acid. It is this which forms, 

 with potash, the bard coat of the polishing rush, the outer 

 covering of the stalks of grasses. Wheat, rye, oats, barley, 

 owe their support to this covering of silica. It cases the 



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