1922.] Basic Slag : Second Interim Report. 



533 



(1) We have included a t\^ical North African mineral phos- 

 phate in our trials at llothamsted, and have arranged for a 

 trial with Nauru phosphate. 



(ii) We are keeping in close touch with, and are repeating 

 side by side with our own experiments at Rothamsted, the 

 experiments on mineral phosphates and basic slag now being 

 carried out in various counties by the agricultural organisers 

 under the a^gis of the Agricultural Education Association, and 

 this is facilitated by the circumstance that the Chairman of 

 your Committee is also Chairman of the Experiments Com- 

 mittee of the Association. 



6. Field Trials. — Owing to the exceptionally severe drought 

 of 1921 veiy few results were obtained in any of the field trials, 

 and in any case the trials must extend over several seasons before 

 we can put for^^ard definite conclusions. 



So far as our present information goes : — 



(a) The high soluble open hearth basic slags have the same 

 agi^cultural value per unit of phosphoric acid as the old 

 Bessemer slags. 



(h) The low soluble slags have a smaller value, but in some 

 circumstances the difference is not markedly great. There is, 

 however, considerable diversity in effectiveness, and we have 

 reason to believe that this group includes materials of very 

 different natures, though the citric solubility test fails satis- 

 factorily to distinguish between them. 



(c) The mineral phosphates also have a smaller value, but 

 again in some circumstances not as much less as might have 

 been expected. 



It is hoped that as a result of these trials we may ultimately 

 be able : — 



(1> To map out the country into regions where the high 

 soluble sla^ can, and where it cannot, effectively, be replaced 

 by low soluble slags and mineral phosphates ; 



(2) To advise the Ministry whether the annual output of 

 some 70,000 to 140,000 tons of very low gi'ade slag (under 

 15 per cent, phosphate) at present not recommended for use 

 by the farmer, could with advantage be used after being 

 admixed in any way with mineral phosphates. 



7. Solubility Test.— Our experience with slagr^ of different 

 solubilities leads us to conclude that the official sohilMlitv test 

 needs revision. 



