66 FUNDAMENTALS OF AGRICULTURE. 



1. That which is immediately available to plants and 

 is soluble in water, namely, soluble phosphoric acid. 



2. That which is soluble to the roots of the plants but 

 is insoluble in water, namely, reverted phosphoric acid. 



3. That which is insoluble to the roots of plants but 

 is soluble in strong acids. The phosphoric acid in 

 phosphate rock is in the insoluble form. The sum 

 of the soluble and the reverted phosphoric acids is 

 called available phosphoric acid, because the plant can 

 easily use it for food. 7"he sum of the available and 

 the insoluble phosphoric acids is called total phos- 

 phoric acid. 



Bones. All bones contain phosphoric acid. The 

 phosphoric acid is mostly in the insoluble form. On 

 this account the phosphoric acid in bones is slowly 

 available for plant food. Sometimes bones are 

 treated with sulphuric acid to render the phosphoric 

 acid available. The product is then called dissolved 

 bone. 



Potash. Most of the potash used for fertilizer is 

 derived from mines in Germany. Kainit, muriate of 

 potash and sulphate of potash are the names of these 

 salts. Kainit is the crude product of the mines. It 

 contains about 12 per cent, potash. Muriate of pot- 

 ash and sulphate of potash are manufactured from the 

 crude salts found in these German mines. They con- 

 tain about 50 per cent, potash. All these potash salts 

 are soluble in water and great care should be exercised 

 in their application to the land. 



EXERCISE. Write in your note-book the names of the fertilizers 

 you have seen. Describe them. Under which class do they belong? 

 Try to procure samples of the different fertilizers mentioned in this 

 section. If they cannot be obtained in your town, write to the near- 

 est fertilizer factory and you can easily get them. Have the pupils 

 examine them and require the pupils to become proficient in naming 

 them. 



