14 FERTILISERS AS AN AID TO 



tion of citric acid which is presumed to represent 

 the action of organic acids that may be present 

 in the soil. As it is a by-product, its composi- 

 tion is variable, though good qualities will con- 

 tain 38 per cent, or more of total phosphates, but 

 by far the larger quantity is of lower grade. Slag 

 is often sold as " 80 per cent, soluble " ; that is to 

 say, 80 per cent, or four-fifths of the total phos- 

 phates is soluble in a standard solution 

 ^ c ^ nc acid, but farmers must not be 

 in sfl. misled into thinking that this means 

 water-soluble phosphate. The term 

 u Soluble Phosphate " has for more than half a 

 century been understood to apply solely to the 

 water-soluble phosphate in superphosphate and 

 similar dissolved phosphates. ' Eighty per 

 cent, soluble" means that, presuming the basic 

 slag contains 38 per cent, of total phosphates, 

 only 30.40 per cent, of the phosphates would be 

 in an available form. The efficiency of this 

 fertiliser also depends on the " grist " or fineness 

 of grinding, which should be such that 80 per 

 cent, will pass through a standard sieve having 

 10,000 holes to the square inch. 



It should be borne in mind that as basic slag is 

 a very heavy material, its covering properties are 

 not so great as a lighter or more bulky article. 

 There is a widespread notion that basic slag 

 can be advantageously used to re- 

 store lime, and statements are habit- 

 Basio'siag. ua lly made that it contains 20 to 25 

 per cent, of caustic or free lime. 

 Such statements as these are misleading. Ex- 



