149 



More or less metallic iron is inclosed in the coarse slag which is generally thoroughly 

 removed from 'he ground material by the magnet. 



MANURIAL VALUE. 



The manorial value of the slag was not recognized for a long time. Finally experi- 

 ments 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 prepa- 

 ration of the slag for fertilizing purposes, when its value was first recognized, consisted 

 in having it finely irnnmd in especially prepared mills, so that 75 per cent would pass 

 through a sieve with perforations 0.17 mm in diameter. This requirement was sug- 

 gested by M. I-Mei>cher, who used the slag with much success in improving the condi- 

 tion of marsh and meadow lands. 



\l \ ni'ii.s FOR DETERMINING AVAILABILITY AND ADULTERATION. 



Previous to 1890, by means of pot experiments, as well as by laboratory investiga- 

 tion-. Wanner demonstrated that tin- phosphoric acid in different slags of the same 

 of fineness vari.-d in its availability from 30 to 90 or more per cent, and, further, 

 thai many brand.- were adulterated with Belgian or other insoluble mineral phos- 

 phate-;. The method therefore of determining the value of a slag by the percentage 

 .il ph"-phoric acid present and the degree of fineness was of secondary impor- 

 tance. 



In order to detect adulteration with mineral phosphates, Wagner originally used a 

 dilute Dilution of -itrate of ammonia and free citric acid. The phosphoric acid in 

 all .f the mineral pho-phate< \va> sparingly soluble in such a reagent, while an unadul- 

 terated. hL'h -ride >|;,,_, .^ve up 80 to 90 parts of its phosphoric acid. Further investi- 

 gations on various soils with many brands of slag made clear that the results obtained 

 f i ..MI p.. t experimei ponded quite well with those secured by means of the 



.. id -olntion Thi- may be illustrated as follows: 



Dt / ' iliihilitii of phosphoric add. * 



Etemlta similar to these were secured by Maercker,& who stated that "the results 

 removed all doubt that the citrate solubility and plant experiments were so nearly 

 proportioned that one had the same right to value the slag according to its content of 

 phosphoric arid soluble in citrate solution as to value the superphosphate by its con- 

 tent of water-soluble phosphoric acid." 



flChemiker Zeitung, 1895, No. 63; also Dimgungsfragen, 1896, No. 1, p. 16. 

 *>Landw. Presse, 1895, No. 82. 



