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;* aé. wt. 39.—When heated in the 
air, this metal burns with a beautiful violet light, and 
forms potash. 
Potash, K,O, 94, is the alkali, and base of the potash- 
salts. \ 
Hydrate of Potash, K,O, H,O, 112, or K H O, 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,O, water being set free. 
SODIUM AND ITS COMPOUNDS. 
Sodium, Na,+ 23.—Burns with a brilliant, orange-yellow 
flame. 
* From the Latin name Kalium. 
4 From the Latin name Vatréum. 
