78 EXPERIMENT STATION. [Jan. 



Manueial Value of Slag kecognized. 



The maniivial value of the slag was not recognized for a long- 

 time ; finally experiments revealed that a considerable portion of 

 its phosphoric acid was soluble in dilute citric and carbonic 

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

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

 first recognized, consisted in haviug it finely ground 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, who used the slag 

 with much success in improving the condition of marsh and 

 meadow lands. 



]\[KTirODS FOR DETERMINING AVAILABILITY AND AdULTERATIOX. 



Previous to 1800, 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 00 or more per cent., and, 

 further, that many brands Avere adulterated with Belgian or 

 other insoluble mineral phosphates. 



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

 slag by the percentage, of total phosphoric acid present aud the 

 degree of fineness, was of secondary importance. 



In order to detect adulteration with mineral ph<;)sphates, 

 Wagner originally used a dilute solution of citrate of ammonia 

 and free citric acids. -^ The phosphoric acid in all of the mineral 

 phosphates was sparingly soluble in such a reagent, while an 

 unadulterated high-grade slag gave up 80 to 00 parts of its phos- 

 phoric acid. Further investigations on various soils with many 

 brands of slag made it clear that the residts obtained from pot ex- 

 periments corresponded quite avcII with those secured by means 

 <:>f the citric acid solution. This may be illustrated as follows : — 



' Chemiker Zeitung No. 63, 1895; also Dunguiigsfra};cn Heft I., p. 1(5, von P. Wagner, 

 1896. 



