IV] PHOSPHATIC MANURES 69 



known as superphosphate, by treating the bone with 

 sulphuric or other acids. This proved remarkably 

 effective on turnips; and he took out a patent in 

 1842 and commenced the manufacture on a large 

 scale. But as the source of the calcium phosphate 

 was immaterial, he used mineral phosphates and 

 guanos instead of bones. 



Another source of phosphatic manures was opened 

 up in 1879 when Thomas and Gilchrist introduced 

 their process for removing the phosphorus from iron 

 during its conversion into steel. At first the agri- 

 cultural value of the basic slag thus produced was not 

 recognised, but it was slowly revealed by the experi- 

 ments of Wrightson and Munroe in 1885, and of other 

 agriculturalists. 



Phosphatic guanos, brought from the Pacific 

 Islands, fish guano worked up from refuse fish, and 

 meat guano from imported meat, contribute in a 

 lesser degree to the farmers' supply. 



As a result of having these large supplies of 

 phosphates from various parts of the world, farmers 

 now very generally add phosphates to their land, and 

 thus remove the limiting factor which had in many 

 cases kept down the crops. Concurrently with the 

 increased use of phosphates there has been a marked 

 increase in soil fertility, the yields of turnips in 

 particular have gone up very much, and there have 

 been very great improvements in the pastures. More 



