78 EXPERIMENT STATION. [Jan. 



Manukial Value of Slag kecognized. 

 The mannrial value of the slag was not recognized for a long 

 time ; finally experiments revealed that a considerable portion of 

 its i^hosphoric acid Avas soluble in dilute citric and carbonic 

 acids, which led to successful lield experiments. The only prep- 

 aration of the slag for fertilizing purposes, when its value was 

 first recognized, consisted in having it finely gromid in espe- 

 cially prepared mills, so that 75 per cent, would pass through a 

 sieve with perforations of .17 millimeter diameter. This re- 

 quirement was suggested by M. Fleischer, Avho used the slag 

 with much success in imi)roving the condition of marsh and 

 meadow lands. 



Methods for determining Availability and Adulter/Vtion. 



Previous to 1890, by means of pot experiments as well as by 

 laboratory investigations, Wagner demonstrated that the phos- 

 phoric acid in different slags of the same degree of fineness 

 varied in its availability from 30 to 90 or more per cent., and, 

 further, that many brands were adulterated with Belgian or 

 other insoluble mineral j^hosphates. 



The previous method, therefore, of determiuing the value of a 

 slag by the percentage of total phosjihoric acid jiresent and the 

 degree of fineness, was of secondary imjxu'taiice. 



In order to detect adulteration with mineral phosphates, 

 Wagner originally used a dilute solution of citrate of ammonia 

 and free citric acids, -^ The phos])horic acid in all of the mineral 

 phosphates was sparingly soluble in such a reagent, while an 

 unadulterated high-grade slag gave up 80 to 90 parts of its phos- 

 phoric acid. Further investigations on various soils with many 

 l)rands of slag made it clear that the results obtained from pot ex- 

 periments corresponded quite well with those secured by means 

 of the citric acid solution. This may be illustrated as follows : — 



1 Cheniiker Zcitung No. 63, 18U5; also Dungungsfraf,aMi Ileft J., p. 16, von P. Wjigner, 



1896. 



