156 CHEMICAL FERTILIZERS 



condition of basic superphosphate is excellent, as it is 

 a dry, fine powder, easily distributed either by hand or 

 machine. The drill is never clogged, and it does not adhere 

 to the hand in hot, damp weather. The material is, however, 

 very bulk}^ occupying from two to three times the space 

 occupied by the same weight of basic slag. Basic super- 

 phosphate is particularly advantageous for use with turnips 

 or other crops which do badly under acid conditions. This 

 mixture has not come into much favour, because it is 

 somewhat expensive to produce ; if both superphosphate 

 and lime are necessary, it would be more beneficial to 

 apply the lime to one crop of the rotation and the superphos- 

 phate to another. Such double distribution may entail slight 

 extra expense in actual application to the field, but it would 

 prove more profitable. During the war period there was a 

 time when the supply of sulphuric acid was very short, so 

 that efforts were made to economize its use by treating 

 superphosphate with finely-ground rock phosphates. With 

 such a mixture, much of the phosphate ceased to be soluble 

 in water, but was soluble in weak acids or ammonium citrate. 

 With the return of plentiful supplies of sulphuric acid, this 

 variety of phosphatic manure has again fallen into the 

 background. Actual experimental trials to compare basic 

 superphosphate against ordinary superphosphate have not 

 shown any particular advantage. It is more economical 

 and convenient to use rock phosphate than to use lime for 

 drying superphosphate, see p. 187. 



' ' Tetraphosphate ' ' of Lime. The cost of production 

 of superphosphate has led to the commercial development 

 of the so-called " tetraphosphate " of lime, invented by 

 Professor Stoppani in 1911. It is made by heating finely- 

 ground natural phosphates with 5-6 % of a mixture 

 of calcium, magnesium and sodium carbonates to a temper- 

 ature of between 600 and 700 C. (1100 and 1300 F.). 

 The calcined mass is moistened, and then diluted with earth 

 or sand, until its phosphate content is reduced to about 40 % 

 tri-calcium phosphate. This material is manufactured in 

 Italy, at L,uxor on the Nile, and at Kosseir on the Red Sea 



