ESTIMATION OF ALUMINA AND FERRIC OXID 257 



average of 1.2 milligrams of alumina. The iron, therefore, has 

 a slightly disturbing effect when present in large quantities. 



Solutions containing aluminum sulfate, ammonium phosphate 

 and five grams of ammonio-ferric alum yielded apparently larger 

 quantities of alumina, by the usual methods, than the theoretical 

 amount. When these solutions, however, were previously treated 

 with thiosulfate the theoretical amounts of alumina were ob- 

 tained. 



Effect of Calcium Salts. The presence of calcium salts pro- 

 duces even less disturbance in the results than iron compounds. 

 The addition of two grams of calcium phosphate gave no indi- 

 cation of alumina in the final results. When aluminum phos- 

 phate was present in the same quantity as the calcium salt, the 

 theoretical yield of alumina was 74.3 milligrams instead of 70.5 

 milligrams, doubtless due to the mechanical entanglement of other 

 compounds. When a second precipitation was employed, this error 

 disappeared. There was obtained an average of 31.5 milligrams 

 of alumina where the theoretical yield was 31.9 milligrams. 



From the foregoing results the conclusion seems warranted 

 that aluminum phosphate can be quantitatively separated by a 

 soluble thiosulfate and ammonium chlorid reagent from a hydro- 

 chloric acid solution of iron, alumina, and lime phosphates con- 

 taining only a small amount of sulfates. The statement of many 

 observers, that theoretical results on aluminum phosphates can 

 only be obtained in the presence of an excess of phosphoric acid, 

 has been confirmed. The error produced by precipitating a sec- 

 ond time without adding phosphoric acid amounted in some cases 

 to two milligrams alumina. 



The Effect of Magnesium, Sodium and Potassium Salts. Salts 

 of sodium, magnesium and potassium were added to the solutions 

 containing alumina before precipitation as phosphate, and it was 

 found that they exerted no disturbing influence on the results 

 obtained. 



The Effect of Sulfates. In these cases the removal of silica 

 is necessary and the property of the insolubility of silica in sul- 

 furic acid was used as the basis of separation. The method of 

 9 



