166 



Composition of Basic Slag 



containing the most lime show the greatest and that containing the 

 least lime the least deflexion. 



The flrst action of the carbon dioxide would almost certainly be 

 the conversion of the free lime into carbonate. The mechanism of the 

 following reactions comprising the conversion of carbonate into bi- 

 carbonate and the solutions of the phosphoric acid compounds is quite 

 obscure. It would be reasonable however to expect, assuming the 

 soluble phosphoric acid compound to be the same for the four slags, 

 that the slag containing the least quantity of free lime should show 

 the highest percentage of phosphoric acid soluble at the first extraction. 

 This is precisely what occurs. 



Thus owing to the small mass of the carbon dioxide entering into 

 the reaction, the extent to which the phosphates are attacked is masked 

 by the presence of varying quantities of free lime. Hence it follows 

 that although the natural solvent in the soil is carbon dioxide, it is 

 not possible in the case of basic slag to make use of it as a solvent 

 for the determination of the soluble phosphoric acid. 



It would seem probable, from the fact that the logarithmic curves 

 approach to straight lines and that they run fairly parallel to each 

 other, that the substance attacked is essentially the same in all of the 

 slags. The probable composition of this compound will be discussed 

 later. 



Further determinations were made of the amount of phosphoric 

 acid soluble in a 1 "/« solution of citric acid. 



In this case three extractions were made. The results are given 

 in Table II. 



Table II. 

 Phosphoric Acid soluble in 1°/^ Citric Acid. Shaken for 24 hom's. 



Here in presence of a much larger mass of acid the small amount 

 of lime has no longer any eifect. Further, in 3 of the 4 slags as 

 much as 93 — 97 "/o of the total present is dissolved. It is worthy of 

 note that in the case of C and D the percentage of total phosphoric 



