PROPERTIES OF ELEMENTS OF SOIL. 53 



full white lieat. This is the only case where alumina stands 

 next to potash. 



5th. They are all fusible, in the order of potash, lime, 

 magnesia, alumina. 



6th. They have already been described as definite combi- 

 nations of metals and oxygen (56). The same law governs 

 their combinations with water. Such compounds are termed 

 hydrates, from "wrfor," water. Water is a compound of 

 eight parts of oxygen, and one part of hydrogen, forming 

 one part of water, whose equivalent is 9. Taking the num- 

 ber representing the base (56), or rather the basic oxide, 

 the equivalents of the hydrates are obtained by adding to 

 each, 1 part = 9 of water. Thus — 



Pota«h, 48 united with 9 water, forms 57 caustic potash. 

 Soda, 32 " 9 " " 41 " soda. 



Ijme, 28 " 9 ♦' " 37 " slacked lime. 



Magnesia, 20 " 9 *' '< 29 " magnesia. 



63. The same law pervades all these various combinations. 

 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 metalloids. 



64. The gradual passage of the characters of the metallic 

 elements of the silicates, into that of the metalloids, is to be 

 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 silicon, sulphur, phos- 

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

 need only to be mentioned. 



65. The rrietalloids have common properties. 



1st. They all combine with the pure base of silicates (46), 

 and form siliciurets, phosphurets, carburets, sulphurets. 

 Thus are formed carburet of iron, or plumbago, sulphuret 



