C. G. T. MoRisoN 107 



acid, soluble in carbon dioxide solution, is the same, whereas in the case 

 of the citric acid solution it is vastly diffcreut. This would suggest in 

 the case of D the presence of compounds unattacked by the carbon 

 dioxide. 



It is a well-known fact that the effect of fine grinding, which 

 will increase very much the surface in contact with the solvent, has a 

 very large effect on the solubility of basic slag. That this has no effect 

 on the very soluble phosphates is evident from the results with carbon 

 dioxide, as G and D both show the same percentage of total phosphoric 

 acid soluble, although the amount of G passing through a 0'2mm. sieve 

 is 76'60, while of D 98-21. The effect of the grinding is however shown 

 in the citric acid solution. Thus it would appear that in basic slag there 

 are at least two sources of phosphoric acid, one of which is very readily 

 soluble in a weak acid like carbon dioxide, and one or more which are 

 attacked by citric acid to an extent depending on the amount of surface 

 exposed. 



A portion of B was finely ground so that the whole passed through 



a 0'2 mm. sieve and citric acid extractions made as before. 



1st 

 1st 2nd 3rd Total Total 



B. Original sample 16-23 1-098 -045 IB-fil -8723 



Finely ground sample... 17-28 1-022 -099 18-()1 -9286 



As regards the more difificultly soluble phosphate, as the solubility 

 seems to depend so much on the surface of the slag, probably also the 

 time during which the two are in contact is an important factor. 



That this is so is seen in the case of B. Two series of determinations 

 being made, one with 1 ^o citric acid shaken for 24 hours as above and 

 another for ^ hour with 2 7o citric acid as recommended under the 

 regulations of the Board of Agriculture, the figures are given below: 



J hour 1st 4 hour 



1st 2nd Total 2-1 lumrs IstT-i hours 



A. 24 hours... 14-020 1-810 15-7r)0 



A hour ... 13-13 1-808 14-938 -985 -941 



B. 24 hours... 16-750 1-060 17-810 



^hour ... 14-460 2440 16900 "949 -092 



It will be seen that the total dissolved may be regarded as the 

 same, but considering the first extraction only there is a considerable 

 difference and apparently a difference by no means the same for different 

 samples of slag. 



The question as to what is the sohible phosphatic compound in basic 

 slag has been regarded as settled for a long time. It has always been 



