MINERAL FERTILIZERS. 



Percentage of Oak. Beech. 



Potassium oxide 8.43 15.83 



Sodium oxide 5.64 2.79 



Sodium chloride . 0.02 0.23 



Calcium oxide, or lime 74-63 62.37 



Calcium sulphate 1.98 2.31 



Magnesium oxide, or magnesia 4.49 11.29 



Iron oxide, or ferric oxide 0.57 0.79 



Phosphoric pentoxide or phosphoric acid. 3.46 3.07 



Silica 0.78 1.32 



77 



IOO.OO IOO.OO 



172. The ash contains all the mineral matter 

 which the plant derives from the soil, and is in a 

 good condition to be used again as plant-food. The 

 potassium and sodium salts are easily washed out 

 by rains, being very soluble in water. In the pro- 

 cess of making soap, ashes are leached for the pur- 

 pose of obtaining these two alkaline metals. Other 

 substances, however, remain, so that even leached 

 ashes are valuable as a manure. 



173. A compost is simply a mixture of differ- 

 ent fertilizing materials. They are generally heaped 

 together and allowed to ferment, or decompose. 

 Organic matter, such as straw, chips, cotton-seed, 

 dead animals, refuse from slaughter-houses, etc., 

 must undergo decay or putrefaction before they be- 

 come valuable as manure, and in doing so they give 

 off ammonia which will be lost unless they be mixed 

 with earthy or other inorganic matter to absorb the 

 gas as fast as formed. Composting is the art of so 



