112 THE PEOPLE'S FARM AND STOCK CYCLOPEDIA. 



in vegetable matter. The acids produced in such soils decom- 

 pose the phosphate, rendering it more soluble arid the acids 

 harmless. 



SUPERPHOSPHATE. Phosphoric acid in bones, or rock phos- 

 phate, is in combination with lime; in form called by chemists 

 tricalcic phosphate. This form is very insoluble. When an acid 

 such as sulphuric is added to this tricalcic phosphate it takes 

 part of the lime, and of course the compound of lime and phos- 

 phoric lime that is left, containing less lime, has a larger propor- 

 tion of phosphoric acid. This new combination is known by 

 chemists as bicalcic and mono-calcic phosphate, according to the 

 amount of lime that is removed, but it is commonly known as 

 superphosphate. Its advantage as a fertilizer over bones or 

 rock phosphate arises from the fact that it is more soluble. 

 Rock phosphate is often converted into superphosphate by 

 treatment with acid, and is then called "Dissolved Rock." 



Commercial " superphosphate " is a substance of very uncer- 

 tain composition. It is usually made from bones treated with 

 acid, to which is added slaughter-house refuse, nitrate of soda, 

 and sometimes other more questionable materials to bring up the 

 per cent of nitrogen. Much of it is made by treating the re- 

 fuse bone black of the sugar refineries with acid. As the bone 

 black contains phosphoric acid but no nitrogen, either slaughter- 

 house refuse or nitrate of soda is usually added to make it show 

 a due proportion on analysis. When superphosphate is mixed 

 with the soil it often combines with more lime, and returns to its 

 original condition of " bone phosphate " or. tricalcic phosphate ; 

 but this new formed phosphate is in a state of such fine division 

 that it is readily acted on by the roots of plants. 



GUANO. This is the excrement of sea-fowls, which in some 

 of the Pacific islands has accumulated for ages. There are two 

 kinds, one found on islands where rain never falls. This is rich 

 in nitrogen, potash, and phosphoric acid. The other kind has 

 had the nitrogen and potash washed out by the rains, and con- 

 tains phosphoric acid only. This latter kind is often treated 

 with sulphuric acid and converted into superphosphate before 

 being sold. 



