THE ACETATE METHOD 231 



of superphosphates by treatment with sulfuric acid their content 

 of iron and alumina becomes a matter of importance. By reason 

 of the poor drying qualities of the sulfates of these bases their 

 presence in any considerable excess of a few per cent, becomes 

 exceedingly objectionable. The quantity of sulfuric acid re- 

 quired for the formation of the sulfates is also a matter of 

 economic importance. The accurate estimation of these ingre- 

 dients is not only then a matter of scientific interest, but one of 

 great commercial significance to the manufacturer. 



The conventional methods so long in use depending on the 

 precipitation of the iron and alumina as phosphates in the pres- 

 ence of acetic acid have been proved to be somewhat unreliable. 

 Not only does the acetic acid fail to prevent the precipitation of 

 some of the lime, but it also dissolves more or less of the iron 

 and aluminum phosphates. The solution of the precipitate and 

 its reprecipitation by the addition of ammonia, may free the sec- 

 ond precipitate from lime, but it increases the error due to the 

 solubility of the aluminum salt. The methods recently introduced 

 for the estimation of iron and alumina in presence of excess of 

 lime and phosphoric acid are not entirely satisfactory, but are the 

 best which can now be offered. 



204. The Acetate Method. The principal of this process is 

 based on the fact that in a solution containing iron, alumina, 

 lime and phosphoric acid, the iron and aluminum phosphates can 

 be thrown down in a slightly acid solution by ammonium ace- 

 tate while the calcium phosphate remains in solution. The acidity 

 h; the older methods is due to acetic and can be secured by making 

 the solution slightly alkaline with ammonia and adding acetic to 

 slight acidity. One of the methods of conducting the operation 

 is that of C. Glaser. 89 This modification of the older processes is 

 based on the assumption that at 70 the iron and aluminum phos- 

 phate is quantitatively precipitated by ammonium acetate in a 

 dilute solution containing no free chlorin and that the mixed 

 precipitate of iron and aluminum phosphates obtained at this 

 temperature is free of lime. The operation is conducted in the 

 following manner: 



The hydrochloric acid solution of the phosphate must contain 

 M Zeitschrift fur analytische Chemie, 1892, 31 : 383. 



