t 548 ] 



893. Super. In Europe the rapidity of the action of 

 bones in soil is increased by treatment with sulphuric acid, by 

 which tri-calcic phosphate is rendered soluble being converted 

 into monocalcic phosphate. Bones, boneash and mineral 

 phosphates, powdered and treated with sulphuric acid go to 

 form the manure known as 'super' or super phosphate of lime. 



894. Caprolites are harder still than bones and even 

 in a powdered state they act slowly in the soil, and they 

 are more difficult to grind than bones. Dissolved with 

 sulphuric acid, bones, coprolites and apatite resolve them- 

 selves into stiper. More than half a million ton of super is 

 made annually in England alone for manurial purposes, the 

 reaction that takes place may be expressed by the formula 

 Ga3P20 8 + 2H 2 SO4 = CaH 4 P 2 O8+2CaSO. 1 . The sulphuric acid 

 first decomposes the CaCO 3 present and manufacturers there* 

 fore do not like the presence of much CaCOs in the bones 

 or minerals used. 



895. The sulphuric acid used in the manufacture of super 

 is 'chamber acid,' which is the cheapest of the three kinds of 

 commercial sulphuric acid, known respectively, as Oil of 

 Vitriol (sp. gr. 1*89), Brown Acid (sp. gr. 1*72) and Chamber 

 Acid (sp. gr. r6). It contains about 69 per cent, of H 2 SO 4 . 

 loo parts of pure CasPsOa require 91 parts of Chamber acid 

 to act on it, while 100 parts of CaCOs require as much as 

 140 parts; 100 parts of Fo20s require 262 Par ts an d l o parts 

 of A1 2 O 3 require as much as 405 parts of Chamber acid to 

 act on the Fo 2 O and A^Os respectively. The freer therefore 

 the mineral is from CaCOs, FesOa and A1 2 O 3 the better it is. 



896. Super is manufactured in the following way ! The 

 raw bones or mineral phosphates are finely powdered with a 

 powerful mill* This powder is placed in a closed vessel or 

 chamber which is called mixer, the necessary quantity of 

 sulphuric acid being dripped into the chamber by slow degrees 

 from a tank above it. The gases given off pass out through 

 a long tube where they gradually condense and pass out in 



