ESTIMATION OF ALUMINA AND FERRIC OXID 255 



monium acetate, after removing iron, lime, etc., with caustic soda. 13 



The thiosulfate has nothing to do with the precipitation, ex- 

 cept that it is an exact method of obtaining the desired neu- 

 trality. Thomson has devised a method in which he makes use 

 of this principle, neutralizing with ammonia and using a delicate 

 indicator to determine neutrality. 16 



Study of the Proposed Method. One of the first problems pre- 

 .sented in the study of any method for the determination of 

 alumina as phosphate is the composition of the ignited phosphate. 

 While there is a general agreement that the normal phosphate 

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

 It is not certain that it is always obtained, even under these condi- 

 tions. 17 



Wash Solutions. It seems that the true solution of this prob- 

 lem can only be obtained by a study of the solutions used in wash- 

 ing the precipitate. Besides waters of all temperatures, solu- 

 tions of various salts, such as five per cent, ammonium nitrate, 

 ammonium chlorid, one per cent, ammonium nitrate plus 0.02 per 

 cent, ammonium phosphate, and dilute ammonium acetate, have 

 "been proposed and used by many investigators. These various 

 washes possibly account for the variations from the normal, so 

 fiequently noted. The recently precipitated phosphates of iron 

 and aluminum, when freed from adhering salts, are slightly solu- 

 ble, or rather are dissociated, in water of any temperature. Those 

 who have apparently used water successfully as a wash probably 

 did not wash enough, only three or four times, to remove the 

 adhering salts. Cold ammonium or sodium acetate also slowly 

 dissolves aluminum phosphate. 



The effects of the following wash liquors have been studied: 



Water at from 60 to 70 C. 



Five per cent, ammonium nitrate at from 60 to 70 C. 



One per cent, ammonium nitrate at from 60 to 70 C. 



Five per cent, ammonium nitrate and 0.02 per cent, ammonium 

 phosphate at from 60 to 70 C. 



t5 Bulletin de la Socie'te' chimique, de Paris, 1896. [3], 15 : 118. 

 16 Journal of the Society of Chemical Industry. 1896, 15 : 868. 

 117 Chemiker-Zeitung, 1897, 21 : 264. 



Blair, Chemical Analysis of Iron, 6th Edition, 1906 : 196. 



.Sooth Carolina Agricultural Experiment Station, Bulletin 2, 1891. 



