38 PROPERTIES OF ELEMENTS OF SOIL. 



binations. There are strong resemblances in the 

 alkaline family, which show their relation, yet each 

 is marked with its individual peculiarities. Alumina 

 stands alone, and seems a natural link connecting 

 the silicates with the urets. 



64. The gradual passage of the characters of the 

 metallic elements of the silicates, into the unmetallic 

 of the urets is observed. The first, show alkaline 

 powers by combining with oxygen. Exhibited in 

 the highest degree by potash, and lowest in alumina, 

 which shows both alkaline and acid properties. By 

 the last, it is allied to urets, silicon, sulphur, phos- 

 phorus, carbon. The three last are so well known, 

 that they need only to be mentioned. 



65. The characters of the class urets, are as fol- 

 lows : 



1st. They all combine with the pure metallic 

 base of the alkaline division of silicates, (46) and 

 form siliciurets, phosphurets, carburets, sulphurets. 

 Thus is formed carburet of iron, or plumbago, sul- 

 phuret of iron, or iron pyrites, sulphuret of potas- 

 sium, or liver of sulphur. 



2d. The urets chemically combine with each oth- 

 er. Thus are formed sulphuret of carbon, and sul- 

 phuret of silicon. 



3d. The urets all form acids, by combining with 



