THE ASH OF PLANTS. 139 



Potassium Hydroxide, KOH, 56, is the caustic 

 potash of the apothecary and chemist. It may be pro- 

 cured 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. Both the oxide 

 and hydroxide of potassium unite to acids forming salts. 



SODIUM AND ITS COMPOUNDS. 



Sodium, N"a,* 23. Burns with a brilliant, orange- 

 yellow flame, yielding sodium oxide. 



Sodium Oxide, or Soda, Na 2 0, 62, is practically lit- 

 tle known, though constantly referred to as the base of 

 the sodium salts. It unites to water, producing the hy- 

 droxide. 



Sodium Hydroxide, or Caustic Soda, NaOH, 40. 

 This body is like caustic potash in appearance and gen- 

 eral characters. It forms soaps with the various fats. 

 While the potash-soaps are usually soft, those made with 

 soda are commonly hard. 



ALKALI-EARTH METALS. The two metallic elements 

 next to be noticed, viz., Calcium and Magnesium, give, 

 with oxygen, the alkali-earths, lime and magnesia. The 

 metals are only procurable by difficult chemical pro- 

 cesses, and from their eminent oxidability are not found 

 in nature. They are but a little heavier than water. 

 Their oxides are but slightly soluble in water. 



CALCIUM AND ITS COMPOUNDS. 



Calcium, Ca, 40, is a brilliant ductile metal having a 

 light yellow color. In moist air it rapidly tarnishes and 

 acquires a coating of lime. 



Calcium Oxide, or Lime, CaO, 56, is the result 



* From the Latin uaiue Natrium. 



