136 PHOSPHATIC MANURES 



may be used for detection. Mineral phosphate is also shown 

 by the presence of fluoride and the absence of free lime. Much 

 carbonate indicates either an old basic slag or the presence of 

 mineral phosphates. If these qualitative tests are equivocal, 

 recourse must be had to analysis. 



124. Analysis of Basic Slag. 



{a) Total Phosphate. — Two grams of the sample 

 are heated in a round-bottomed hard glass flask with 

 20 c.c. of concentrated sulphuric acid until white fumes 

 appear. The liquid is cooled, diluted with distilled 

 water, and made up to 500 c.c. in a measuring flask. 

 The liquid is well shaken, filtered, and the phosphate 

 determined in 50 c.c. of the filtrate ( = 0-2 gram of 

 the slag) by the molybdate method. 



{U) Citric Soluble Phosphate. — Five grams of the 

 slag are shaken in a litre bottle for half an hour with 

 500 c.c. of a solution containing 10 grams of citric acid. 

 The mixture is filtered and the phosphate determined 

 in 50 c.c. of the filtrate. 



ic) Fineness. — The fineness is determined as above 

 {a). 



CHAPTER XIII 



Potash Manures 



With the exception of wood ashes and one or two by-products 

 from the manufacture of glue, etc., nearly all the potash fertilisers 

 are soluble salts derived from the Stassfurt deposits. Large 

 quantities of potash exist in the felspars and other rocks, but in an 

 insoluble condition, and little success has so far attended the use 

 of such materials either in the raw state or after treatment. 



