FERRIC PHOSPHATE AND THE ALKALINE EARTHS 6ll 



and weighed, giving the weight of silica plus sand, from which 

 the weight of sand is deducted to obtain soluble silica. It is 

 inadmissible to separate the soluble silica from the residue after 

 it has been ignited. 



Instead of limiting the quantity of hydrochloric acid used for 

 moistening the dried residue, as suggested above by the official 

 chemists, enough should be employed to fully saturate the mass. 

 The weight of pure ash is obtained by subtracting from the 

 weight of the sample used the sum o-f the weights of carbon, 

 sand, and carbon dioxid. 



519. Ferric Phosphate and the Alkaline Earths. The ferric 

 phosphate, lime, magnesia, and manganese are determined in an 

 aliquot part of the first hydrochloric acid solution and wash- 

 ings obtained above. Fifty or TOO cubic centimeters may be 

 used, corresponding to one or two grams of the original ash. 

 The accurately measured quantity of the solution is carefully 

 treated with ammonia until the precipitate formed on its addi- 

 tion becomes permanent on shaking. Ammonium acetate and 

 acetic acid are then added until the mixture has assumed a 

 strongly acid reaction. The separation of the ferric phosphate 

 precipitate is promoted by gentle warming, and it is separated 

 by filtration without unnecessary delay. If the precipitate be 

 not large the sample contains no manganese and alumina in 

 weighable quantities, and if the filtrate be not red, the precipi- 

 tate is washed with hot water containing a little ammonium 

 nitrate. It is then ignited and weighed as Fe 2 P 2 O 8 and the 

 quantity of ferric oxid computed therefrom. If, however, the 

 precipitate be large, it is well washed as above and then dis- 

 solved in as small a quantity as possible of hydrochloric acid, 

 and the solution is again precipitated as above by the addition 

 of ammonia, ammonium acetate, and acetic acid. The ferric 

 phosphate obtained by the second precipitation is treated exactly 

 as above described. 



In case, however, any weighable quantities of manganese or 

 alumina are present it will not do to weigh the precipitate of 

 ferric phosphate directly even after a second precipitation. Also 

 if the filtrate at first obtained have a red color, the precipitate 



