106 The Phosphates of America. 



CHAPTER VII. 



THE MANUFACTURE OF SUPERPHOSPHATE, PHOSPHORIC ACID, 

 AND " HIGH-GRADE SUPERS." 



THE process of superphosphate manufacture from mineral 

 phosphates is not very generally understood, and while neither 

 very complicated nor difficult, requires a certain amount of 

 chemical knowledge and experience which the majority of those 

 concerned in it do not possess. Hence it follows that no article 

 in the market is more variable, both in its physical condition and 

 chemical composition. 



Nor can this remain a source of surprise when we remember 

 that each manufacturer adopts some peculiar system of his own, 

 and that no two fertilizer factories bear any resemblance to each 

 other. 



We have seen that raw phosphates, whether of animal or 

 mineral origin, are made up of three molecules or parts of lime 

 (CaO) combined with one molecule or part of phosphoric anhy- 

 dride (P 2 O 5 ). The words acid phosphate, superphosphate, water- 

 soluble phosphate, are all used to describe a product obtained by 

 treating these raw phosphatic materials with a sufficient propor- 

 tion of sulphuric acid to transform two out of their three mole- 

 cules of lime into sulphate of lime or gypsum (CaSO 4 ). 



To the lay reader, the chemistry of the mixture will be more 

 readily understood if we briefly explain, that when a piece of pure 

 phosphorus is burnt in contact with dry air it gives off vapors, 

 every two atoms of which combine with five atoms of atmospheric 

 oxygen to form a snow-white powder. This powder is the phos- 

 phoric anhydride above alluded to, and it has a molecular weight 

 of 142. Its chief characteristic is its attraction for water, and if 

 left temporarily exposed to the air it rapidly deliquesces. 



In this moist state it is found to have combined with water in 

 the molecular ratio of 1:3, and its composition has become 



Phosphoric anhydride (P 2 O 5 ) 1 mol. = 142 by weight. 



Water (H 2 O) 3 mols. = 54 



Or, Phosphoric acid (H 3 PO 4 ) 2 mols. = 196 " 



In other words, every 100 parts of it contain 



