PROPERTIES OF ELEMENTS OF SOIL. 37 



feebly. The alkalies form soluble, and the alkaline 

 earths, and alumnia insoluble compounds with car- 

 bonic acid. 



4th. They have all great affinity for water, com- 

 bining with it, and forming what are called hydrates. 

 Potash parts not with this chemically combined wa- 

 ter, by any heat which has been produced ; lime 

 and magnesia give up their water readily, at a red 

 heat ; alumina requires for this purpose, a full white 

 heat. 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 defi- 

 nite combinations of metals, and oxygen (56). The 

 same law governs their combinations with 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 number repre- 

 senting the base, (56) or rather the basic oxide, the 

 equivalents of the hydrates are obtained by adding 

 to each, one part =9 of water : thus — 



Potash, 48 united with 9 water, forms 57 caustic potash. 

 Soda, 32 " 9 " " 41 " soda. 



Lime, 28 " 9 " " 37 " slacked lime. 



Magnesia, 20 " 9 " " 29 " magnesia. 



63. The same law pervades all these various com- 

 4 



