170 Comx>osition of Basic Slag 



tetra-calcium phosphate which supplies the soluble phosphoric acid in 

 basic slag, but a body in which the molecular ratio of phosphoric acid 

 to lime is 1 : 5. 



Consideration of the amounts of phosphoric acid and lime dissolved 

 by carbon dioxide solution affords striking confirmation of this as regards 

 the whole mass of slag. 



If the first three extractions are considered it may be assumed that 

 all the readily soluble bodies have been attacked as well as all the free 

 lime dissolved in the form of bicarbonate. The total lime dissolved 

 also was determined. 



yum of 1st three extractions CaO ^2^5 



SlagD 33-48 7„ 13-69 °/o 



If the 5-56 grams of free lime found by the water extraction method 

 be subtracted there remain dissolved 27-92 7o CaO compared with the 

 phosphoric acid. 



The molecular ratio of these is 



27-92 _ 13-69 



~56~ ■ 142 



•498 : -0964 



5 : 1 



Thus of the total lime present in the slag which was 38-62 "/o. 5-8 

 was as oxide or carbonate, 27*68 was combined in readily soluble form 

 leaving 5-17 combined with the remainder of the phosphoric acid. 



V. F. KroU' in a preliminary note says that the principal constituent 

 of basic slag is a compound hitherto unknown, consisting of a silico- 

 phosphate of lime and ferrous iron, which would seem to agree with the 

 results obtained in the present paper. 



The absence of crystals of tetra-calcium phosphate, which were 

 undoubtedly obtained from basic slag by earlier observers, and the low 

 percentages of free lime now found to be present in the slag, may be 

 correlated with the increased percentage of phosphoric acid in slags 

 of modern manufacture, less lime being nowadays employed in the 

 dephosphorisation process than formerly. 



In conclusion the author wishes to thank the Lawes Agricultural 

 Trust for the use of their Laboratory and to express his great indebtedness 

 to Mr A. D. Hall, who suggested this investigation, and whose kind 

 advice has been invaluable throughout. 



1 SUM und Eisen, no. 19, May 6, 1908. 



