124 HOW CROPS GROW. 



metals. Their oxides are very soluble in water, and are 

 called alkalies. The metals themselves do not occur in 

 nature, and can only be prepared by tedious chemical 

 processes. They are silvery-white bodies, and are lighter 

 than water. Exposed to the air, they quickly tarnish from 

 the absorption of oxygen, and are rapidly converted into 

 the corresponding alkalies. Thrown upon water, they 

 mostly inflame and burn with great violence, decomposing 

 the liquid, Exp. 11. 



Of the alkali-metals, Potassium is invariably found in 

 all plants. Sodium is especially abundant in marine and 

 strand vegetation ; it is generally found in agricultural 

 plants, but is occasionally absent from them. 



POTASSIUM AND ITS COMPOUNDS. 



Potassium, sym. K ;* at. wt. 39. When heated in the 

 air, this metal burns with a beautiful violet light, and 

 forms potash. 



Potash, K 2 O, 94, is the alkali, and base of the potash- 

 salts. 

 Hydrate of Potash, K 2 O, H 2 0, 112, or K H 0, 56, is the 



caustic potash of the apothecary and chemist. It may be 

 procured in white, opaque masses or sticks, which rapidly 

 absorb moisture and carbonic acid from the air, and 

 readily dissolve in water, forming potash-lye. It strongly 

 corrodes many vegetable and most animal matters, and 

 dissolves fats, forming potash-soaps. It unites with acids 

 like K 2 O, water being set free. 



SODIUM AND ITS COMPOUNDS. 



Sodium, Na,t 23. Burns with a brilliant, orange-yellow 

 flame. 



* From the Latin name Kdttum. 

 t From the Latin name Natrium. 



