1922.] Experiments with Phosphates and Slaiis. 



511) 



FIELD EXPERIMENTS WITH ROCK 

 PHOSPHATES AND BASIC SLAGS.- 



L 



• G. S. EOBERTSON, D.Sc, F.I.C. 



Some ten or twelve years ago the Basic Open Heariii Process 

 of manufacturing steel was introduced, and as it bad the advan- 

 tages of being more economical tban the Basic Bessemer Pro- 

 cess and of permitting the more extensive use of our lower 

 grade ores, it has now almost replaced the older process. 



Basic Slag. — The slag which results from the new process 

 is still, to the steel manufacturers, a " basic slag," but it is no 

 longer the "basic slag" with which the farmer has become 

 so familiar and to which he attached so high a value. It con- 

 tains a much smaller percentage of phosphate, the phosphates 

 are of a different type, and in many instances they are far 

 less soluble than those of the old Basic Bessemer Slag. 



For practical purposes basic slags now obtainable may be 

 divided into three types : — 



Type (1) High Grade, containing from 33 to 42 per cent, of phospliatc. A 

 part of this supply consists of the rapidly diminishing rem- 

 nants of the Basic Bessemer Slag, and agriculturists nmst face 

 the p'obabihty "of the complete disappearance of this class 

 of slag. 



Type (2) Open Hearth Basic Slag, containing from 15 to 32 per cent, 

 of phosphate. 



Type (3) Open Hearth Fluorspar Slag, containing from 15 to 32 per cent, 

 of phosphate. 



Types 1 and 2 have a citric solubility of from 80 to 95 per 

 cent, and may be safely taken to be of equal value per unit 

 of phosphate. 



Type 3 has a citric solubility of from 6 to 50 per cent., and 

 it is this type of slag which is of uncertain value. It is im- 

 possible to distinguish Open Hearth Fluorspar Slag from the 

 other types by appearance, and if a purchaser wishes to avoid 

 buying basic slag of this type it is only possible to do so by 

 obtaining a solubility guarantee. 



How much of the present supply is of the Open Hearth 

 Fluorspar type it is not possible to say, but it is certain that 

 the propo rtion is likely to increase in the future, and as it is 



This Article is based on a monograph on "Basic Slags and Rock Phos- 

 phates by Dr. Robertson, recently pubhshed hy the Ca]nbridg<> I'niversitv 

 Press. Tiie Ministry is indobt.«d to Ihc Syndics of the Cand)ri(i<;c Tniversitv 

 Press for pcnnission to utiHso Tables 2, 3 and 4 and Figs. 1 to 5' 



