GERMAN MANUFACTURERS' METHOD 217 



since the slags are cheaper than the superphosphates in California, 

 he recommends their use. He is also in accord with the senti- 

 ment of the association to value these basic slags, at least provi- 

 sionally, by their total content in phosphoric acid and their degree 

 of fineness. 70 



Huston and Jones show that the strength of citric acid, time 

 and temperature of digestion, all exert a marked effect on the 

 amount of phosphoric acid dissolved from slags, as does also the 

 relation of quantity of material to volume of solvent. 71 It was 

 found that even when basicity of the slag was corrected the 

 reaction with citric acid was far from complete in 30 minutes at 

 a temperature of 65. The same conclusion holds with neutral 

 ammonium citrate, though here the differences are not so marked. 

 The work indicates that in a relatively short time all the phos- 

 phoric acid will be dissolved, even by dilute citric acid at any 

 temperature, this indicating, further, that the phosphate of basic 

 slag has practically a uniform composition. 



190. German Manufacturers' Method. In the examination 

 of phosphatic slags, the Union of German Fertilizer Manufac- 

 turers determine total phosphatic acid after solution, (a) in 

 hydrochloric acid, and (b) in sulfuric acid. In the hydrochloric 

 acid method 10 grams of finely ground phosphatic slag, which has 

 passed through a two millimeter sieve, are placed in a flask of 

 one-half liter capacity, 80 cubic centimeters of concentrated hy- 

 drochloric acid added and the mixture evaporated on a sand-bath 

 to a sirupy consistence. The mixture is dissolved in water, treated 

 with a few drops of hydrochloric acid, and after cooling the flask 

 is filled to the mark. In 50 cubic centimeters of the filtrate, after 

 the addition of 100 cubic centimeters of the ammonia-citric acid 

 solution, made up according to the method of Maercker, namely, 

 1500 grams of citric acid, 5000 cubic, centimeters of 24 per cent, 

 ammonia and water to 15 liters, the phosphoric acid is now pre- 

 cipitated by 25 cubic centimeters of the ordinary magnesia mix- 

 ture, stirred for one-half hour in a shaking apparatus, and after 

 standing two hours, filtered and treated as has already been de- 

 scribed for the estimation of phosphoric acid soluble in water. 



70 Bureau of Chemistry, Bulletin 81, 1904 : 169. 



71 Division of Chemistry, Bulletin 49, 1897 : 68. 



