IRON AND ALUMINUM PHOSPHATES 245 



of the salt in a liter. An immediate precipitate is produced at 

 ordinary temperatures, and on heating to 60 it becomes abundant. 

 The addition of ammonium chlorid, phosphate, and nitrate in suc- 

 cessive portions, does not prevent the precipitation. Making 

 the solution more dilute lessens the difficulty. When 20 cubic 

 centimeters of a 10 per cent, solution of ammonium phosphate 

 are first added, followed by the usual quantity of ammonium 

 acetate, a clear crystalline precipitate is sometimes observed. 

 .Experience also shows that the trouble is not due to an excess 

 of the ammonium acetate. 



In treating a solution of iron-aluminum phosphate, in similar 

 circumstances, with the ammonium acetate, it is found that a 

 complete precipitation takes place. 



Since diluting the solution of the calcium salt diminishes its 

 tendency to form a precipitate with the ammonium acetate, the 

 true method of separation seems to lie in that direction. The 

 calcium salt is held completely in solution when the separation 

 is made in the following way : 



The solution containing the mixed phosphates is diluted so as 

 to contain not more than one gram thereof in half a liter. To 

 this is added one drop of methyl orange, and afterwards 

 ammonium hydroxid, until a very slight precipitate is formed. 

 The mixture is heated to 70 and from 20 to 25 cubic centimeters 

 of a 25 per cent, solution of acid ammonium acetate are added, 

 enough to change the rose color of the indicator to orange. The 

 iion-aluminum phosphate is separated by filtration and washed 

 with a hot five per cent, solution of ammonium nitrate. 



The washed precipitate shows no impurity due to calcium, as is 

 proved by dissolving it, reprecipitating and filtering, adding 

 ammonium hydroxid to the filtrate, and heating for a long time. 

 Sometimes a slight troubling of the clear liquid may be observed 

 which may be due to a slight solubility of the iron-aluminum 

 phosphate in washing, an accident that may occur if the tem- 

 perature be allowed to fall below 70, but no weighable amount 

 of material is obtained. If due to calcium phosphate, a greater 

 dilution in the first precipitation will remove even this mere trace 

 of that salt. In the above conditions the contamination of the 



