HALLE METHOD FOR BASIC SLAG 199 



of water added. The rest of the operation is carried on in the 

 usual manner. 



172. Halle Method for Basic Slag. The total phosphoric acid 

 is estimated at the Halle Station by the following process : 49 



Ten grams of the substance are moistened in a porcelain dish 

 with a few drops of water and about five cubic centimeters of a 

 one to one solution of sulfuric acid added, and after the mass has 

 hardened, which takes place very soon, 50 cubic centimeters of 

 concentrated sulfuric acid are added and stirred with a glass rod 

 until evenly distributed throughout the whole mass. In stir- 

 ring this mixture the greatest care must be taken, otherwise some 

 of the substance will remain attached to the sides of the dish, 

 which during later heating would cause loss through spurting. 

 The complete solution takes place after a few hours heating on 

 a sand-bath. During the cooling, the jelly-like mass must be 

 stirred with a glass rod, and after it is cool, by means of a wash- 

 ing bottle, gently along the sides of the dish, water is added, and 

 when the mixture becomes hot it is again cooled and washed 

 into a half-liter flask, which is made up to the mark at a tem- 

 perature of 1 7. 5 and filtered. When the acid filtrate stands for 

 some time there is often a separation of gypsum that, however, 

 does not in any way influence the subsequent analysis, which is 

 made in the usual manner. 



Fifty cubic centimeters of the filtrate, representing one gram 

 of the original substance, are placed in an erlenmeyer. In the 

 case of double superphosphates, which often contain large quan- 

 tities of pyrophosphates, 25 cubic centimeters of the filtrate just 

 obtained, equivalent to 0.5 gram of the substance, are diluted with 

 75 cubic centimeters of water, 10 cubic centimeters of nitric acid 

 of 1.42 specific gravity added, and heated on a sand-bath to con- 

 vert the pyro- into orthophosphates. The heating should be con- 

 tinued until the liquid is reduced to its original volume of 25 

 cubic centimeters. The strongly acid liquid is saturated with 

 ammonia and with the addition of a drop of rosolic acid as an 

 indicator, again acidified with nitric acid, and treated as with 

 superphosphates. 



49 Bieler und Schneidewind, Die agrikultur-chetnische Versuchsstation 

 Halle, a/S. ihre Einrichtung und Thiitigkeit, 1892 : 6r. 



