88 FIRST PRINCIPLES OF AGRICULTURE, 



fore, not uniform in character, the phosphoric acid vary- 

 ing according to the amount of the other substances 

 present. 



It is mined in the provinces of Quebec and Ontario, 

 and separated into various grades at the mines. The 

 mining is expensive, and the necessity for grading in 

 addition makes the cost of production proportionately 

 high. The highest grade of this phosphate is very pure, 

 containing forty per cent of phosphoric acid. 



Iron Phosphate. — This is a waste product from the 

 manufacture of steel from phosphatic iron ores, by what 

 is known as the " basic process.'' It is sold under several 

 names, as "Thomas Phosphate Meal," "Phosphate Slag," 

 " Basic Slag," and " Odorless Phosphate." It is produced 

 in large quantities in England, France, and Germany ; and 

 in those countries is not only one of the cheapest sources 

 of phosphoric acid, but is regarded as a very valuable 

 product. It is not produced to any extent in America, 

 is known under the name of "Odorless Phosphate," and 

 is not largely used. It contains from fifteen to twenty 

 per cent of phosphoric acid, in the form of phosphate 

 of lime, in connection with large amounts of lime and 

 oxide of iron. It is used almost altogether in the form 

 of a fine powder, since it is not suitable for the purposes 

 of the manufacturer. When very finely ground, the 

 phosphoric acid is quite as active as that contained in 

 fine bone meal, and is especially suitable for clay and 

 sandy soils and for meadows. 



Phosphatic Guanos. — Previous to the discovery of 

 the phosphates in South Carolina, these guanos were a 

 very important source of phosphoric acid; they are now 



