156 Appendix. 



Insoluble Phosphoric Acid is the ordinary tri-calcium pliosphate. Tliis 

 form is very insoluble in water and is but very slowly available for plant 

 growth. 



Available Phosphoric Acid consists of the water-soluble and reverted taken 

 together. 



Unavailable Phosphoric Acid consists of tri-calcium phosphate, or that portion 

 not included in water-soluble or reverted. 



Total Phosphoric Acid is the sum of the available and unavailable phosphoric 

 acid. 



Apatite. Considerable apatite has been mined in Canada. It is not very 

 uniform in composition and not so desirable as some other forms of phosphoric 

 acid. 



Bone Ash is the residue left after burning bones. Some of this is imported 

 from South America. 



Bone-Black or Bone-Charcoal is obtained from sugar refining establish- 

 ments where it has been used in purifying syrups and sugars. 



Bone-Black (dissolved) is similar to ordinary bone-black, except that it has 

 been treated with sulphuric acid so that the phosphoric acid is made more easily 

 available. 



Bone Meal consists of ground bones from packing establishments and glue 

 works. Generally the finei- the meal the more easily the phosphoric acid becomes 

 available. 



Bone Meal (dissolved) consists of bone meal which has been treated with 

 sulphuric acid. 



Florida and South Carolina Rock, sometimes called rock phosphates, are 

 mined in large quantities in South Carolina and Florida. The availability of 

 The phosphoric acid contained in these materials depends somewhat upon the 

 degree of fineness to which the substance is ground. 



Dissolved Rock, Acid Phosphate or Superphosphate is prepared by treating 

 the ground rock with sulphuric acid. This treatment makes the phosphoric acid 

 much more easily available. The action of the sulphuric acid is to change most 

 of the tri-calcium phosphate contained in the rock to mono-calcium phosphate. 

 During this chemical change much calcium sulphate (gypsum) is formed, so that 

 dissolved rock or acid phosphate always contains about 50 per cent gypsum. 



Thomas Slag is a waste product obtained during the manufacture of Bessemer 

 .steel. The slag which accumulates while the steel is being made is rich in phos- 

 phoric acid. This slag when finely ground is used, especially in Europe, in large 

 quantities as a fertilizer. 



POTASH SUPPLY. 



There are many materials which contain quite large quantities of potash. 

 In the agricultural sense, that potash is considered of most value which is solu- 

 ble in distilled water. At the present time the main part of the world's supply of 

 potash comes from the mines in Germany. 



Potash is usually aplied either in the form of muriates, sulphate or carbonate. 



The muriate is probably most often used as it is generally somewhat cheaper 

 than other forms. Sometimes for certain crops it is preferable to use the sul- 

 phate. In a very few instances the carbonate is used in preference to either 

 muriate or sulphate. 



