162 SCIENTIFIC AGRICULTURE. 



many minerals, nearly all plants, and in animal bodies. It is 

 most abundant in the green and tender parts of plants, the 

 timber of forest trees contains comparatively little. 



Its powerful action on other metals and earths, its caustic 

 action on vegetable substances, and its almost universal pre- 

 sence in soils and vegetation, show it to be an indispensable 

 element of good soils, and a powerful fertilizer. Potash is 

 rendered more caustic by mixture with quick lime, in this 

 way it is beneficial in compost by facilitating the decomposition 

 of vegetable matters. 



MAGNESIUM. 



Magnesium is found in the minerals, serpentine, talc, steatite, 

 asbestos, augite, chrysolite and hornblende: it is always found 

 combined with acids, or other earths, it is found also in marl, 

 and in small quantities in animal substances. It is a white, 

 silver-like metal when pure, malleable, and fusible at a red heat, 

 not changed by dry air, but slowly oxidized by damp air: it 

 dissolves in dilute acids, giving off hydrogen gas, and forming 

 a salt of magnesia. 



Its equivalent number is 12.7. When heated to redness in 

 the air, or in oxygen, it burns with brilliancy, and forms mag- 

 nesia, or oxide of magnesium: it inflames spontaneously in 

 chlorine. It exists in considerable quantity in nature, par- 

 ticularly in magnesian limestone. 



Magnesia slowly but entirely neutralizes acids ; it is inodorous, 

 white, has a slightly alkaline taste, absorbs and retains water 

 to nearly the same degree as lime, but is less caustic and 

 alkaline. There are several important salts of magnesia, some 

 of which are valuable as fertilizers, and indispensable to the 

 growth of vegetation. 



CALCIUM. 



Calcium is a white silvery metal, heavier than water, 

 having a strong affinity for oxygen, with which it combines 



