BASIC SLAG 



135 



division, and 80 to 90 per cent, of a sample should pass the 100 

 meshes to the linear inch sieve. The active phosphate is insoluble 

 in water, but dissolves in a 2 per cent, solution of citric acid. 

 Fully 90 per cent, of the total phosphoric acid should be thus 

 soluble. Basic slag contains a proportion of free lime and also 

 contains sulphides, a certain amount of carbonates, free iron, and 

 magnetic iron oxide. It is sometimes adulterated with ground 

 mineral phosphate. 



122. Qualitative Examination of Basic Slag. 



(a) Fineness. — Ten grams of the sample are sifted 

 through the 100 meshes to the linear inch sieve 

 (10,000 to the square inch). When no more comes 

 through, the residue is weighed, the weight subtracted 

 from the total weight, and the percentage fineness 

 calculated. 



{b) Carbonates^ Sulphides, Fluorides. — The slag is 

 tested with diluted hydrochloric acid. If any effer- 

 vescence takes place the issuing gas is tested for carbon 

 dioxide (lime water) and hydrogen sulphide (lead 

 acetate paper). 



Fluorides are tested for in the usual manner after 

 treating the slag with strong sulphuric acid. 



{c) Free Iron and Magnetic Iron Oxide. — The 

 presence of these substances is readily shown by 

 their adhering to a magnet passed through a sample 

 of basic slag. 



{d') Lime. — A few grams of the slag are shaken 

 with 50 c.c. of distilled water and filtered. The filtrate 

 is distinctly alkaline to indicators, and will require an 

 appreciable number of drops of decinormal acid to 

 neutralise. 



123. Adulteration of Basic Slag. 



The fertiliser is occasionally sophisticated or imitations made 

 up with ground mineral phosphates. The difference in density 



