216 AGRICULTURAL ANALYSIS 



phoric acid in basic slags, Mach also found that while some forms 

 of the citric method of direct precipitation gave very good results, 

 the molybdate method, especially in the case of sulfuric acid solu- 

 tions of slags, must be regarded, without doubt, as the most re- 

 liable. 



189. Association and Other American Methods for Basic Slag. 

 The question of adopting a method for determining the avail- 

 ability of phosphoric acid in slag, has been before the Association 

 of Official Agricultural Chemists for the past three years, and 

 quite a number of reagents and processes have been proposed for 

 this purpose. The practical absence of this form of fertilizer 

 from the American market has prevented the manifestation of 

 much interest in the discussion. Solubility has been determined 

 in 1.09 ammonium citrate, in one per cent, citric acid, in two per 

 cent, citric acid, and in all these after preliminary treatment with 

 water or with five per cent, sugar solution followed by five per 

 cent, ammonium chlorid solution as suggested by Macfarlane. 88 

 The referee for 1902 shows that the Wagner method indicates 

 about 80 per cent, of the phosphoric acid in slag as available and 

 the ammonium citrate method, 30 per cent. The former is regarded 

 as too high, and the latter, too low. He suggests that a percentage 

 be established that may be regarded as representing the amount 

 of availability, and a method could then be devised to give this 

 amount. 69 While no action was taken, the sentiment of the asso- 

 ciation appeared to be in favor of a valuation based on the deter- 

 mination of phosphoric acid and of fineness as is now the usage 

 in the case of raw bone. 



Hilgard has called attention to the increasing use of phosphatic 



slags in California and attributes their good effects to the large 



quantity of lime in the arid soils. This condition secures the 



reversion of the water-soluble acid in superphosphates within 



the first three or four inches of the surface of the soil. Deep 



plowing is, therefore, necessary to bring the phosphoric acid into 



contact with the lower roots of the crop. Such plowing would 



also mix basic phosphates with the deeper layers of the soil, and 



* Dirision of Chemistry, Bulletin 62, 1901 : 46. 



69 Bureau of Chemistry, Bulletin 73, 1903 : 16. 



