PHOSPHATES AND BASIC SLAGS 185 



potassium chlorate and the whole is intimately mixed. The mix- 

 ture is then placed in a porcelain dish and hydrochloric acid 

 is added, little by little, until the potash salt is completely decom- 

 posed. It is evaporated until the mass is dry. The material is 

 then treated with fuming nitric acid, and the determination of 

 the phosphorus is made by the ordinary gravimetric method. 



By carrying on the operation as described above, a reduction 

 of phosphoric acid is avoided, and the presence of an abundant 

 quantity of potash prevents the formation of basic iron phosphate 

 which is insoluble in nitric acid. 



(2) Citrate-Soluble Phosphoric Acid. One gram of the basic 

 slag or phosphate is placed in a 100 cubic centimeter flask and 

 covered with Wagner's acid citrate solution making the total vol- 

 ume up to 100 cubic centimeters. With frequent shaking the 

 flask is kept at 40 for an hour, or it may be allowed to stand for 

 12 hours at room temperature with frequent shaking. In 50 

 cubic centimeters of the filtrate from this flask the phosphoric 

 acid is determined by the magnesia mixture as described. Since, 

 in the present case, the precipitate of ammonium magnesium 

 phosphate contains some silicic acid it can not be directly ignited 

 but must be treated in the following manner: The precipitate 

 and the filter are thrown into a porcelain dish, the filter paper 

 torn up into shreds with a glass rod, the precipitate dissolved 

 in nitric acid, neutralized with ammonia, acidified with acetic, 

 and treated with uranium solution. The phosphoric acid may 

 also be estimated by the gravimetric method by dissolving the 

 precipitate again in hydrochloric or nitric acid, evaporating to 

 dry ness, and drying for one hour at from 110 to 120, dissolv- 

 ing again in hydrochloric acid, filtering, and washing the precip- 

 itate well. The filtrate, which is now free from silica, can be 

 treated with Joulie's solution, precipitated with magnesia mixture, 

 the precipitate washed, ignited, and weighed as described. The 

 molybdate method is preferred in the estimation of citrate-solu- 

 ble phosphoric acid, especially in slags. For this purpose 50 cubic 

 centimeters of the filtrate from the solution of one gram of slag 

 in 100 cubic centimeters of Wagner's citrate liquid are treated 

 with 100 cubic centimeters of molybdenum solution and 30 cubic 



