I30 



PHOSPHATIC MANURES 



[chap. 



an acid, make it easy to distinguish between basic slag 

 and made-up imitations in which the phosphates are 

 derived from ground phosphate rock. 



Table XXXIII. shows an analysis of the material, 

 in which the most striking feature will be seen to be 

 the large amount of lime and magnesia present — 

 more than would normally combine with the phos- 

 phoric acid, even when allowance has been made for 

 any lime that is free or that may be supposed to be 



Table XXXIII.— Analysis of Basic Slag 

 (Stead and Ribsdale). 



combined with the silica. The analysis alone suggests 

 that basic .slag does not contain the usual tri-calcium 

 phosphate, and its behaviour in the soil and the ready 

 availability of the phosphoric acid strengthen the view 

 that it contains some other compound of phosphoric 

 acid. For example, basic slag is found to be readily 

 attacked by a solution of carbon dioxide or other very 

 weak acid ; a much larger proportion of phosphoric 

 acid goes into solution than would be the case with 

 an equally fine ground sample of tri-calcium phosphate 

 containing the same amount of phosphoric acid. Nearly 



