184 AGRICULTURAL ANALYSIS 



ammonia, and then acid with acetic. This solution is treated 

 with 10 cubic centimeters of sodium acetate and titrated with 

 uranium, as described in ( i ) . As an alternative method, 200 cubic 

 centimeters of the superphosphate solution may be treated with 50 

 cubic centimeters of sodium acetate, allowed to stand for some 

 time, and filtered through a filter of known ash content. In 50 

 cubic centimeters of the filtrate, which correspond to 40 cubic 

 centimeters of the original solution, phosphoric acid may be de- 

 termined as described above. The precipitate, consisting of iron 

 and aluminum phosphates, is washed three times on the filter with 

 boiling water, dried, and ignited in a platinum dish. The weight 

 of ignited precipitate, diminished by the weight of the ash con- 

 tained in the filter and divided by two, gives the quantity of phos- 

 phorus pentoxid which it is necessary to add to that obtained by 

 titration. 



158. Determination of the Phosphoric Acid in all Phosphates 

 and Basic Slags. 



(i) Total Phosphoric Acid: 



Five grams of the fine phosphate meal, or slag meal, are moist- 

 ened in a flask of 500 cubic centimeters content with some water 

 and boiled on a sand bath with 40 cubic centimeters of hydro- 

 chloric acid of from 16 to 20 Beaume. The boiling is continued 

 until only a few cubic centimeters of a thick jelly of silicic acid 

 remain. After cooling, some water is added and the phosphate 

 shaken until the thick lumps of silica are finely divided. The 

 flask is then filled to 500 cubic centimeters and its contents fil- 

 tered. Fifty cubic centimeters of the filtrate are mixed with 15 

 cubic centimeters of the Joulie solution and treated in the manner 

 described with magnesia mixture, precipitated, ignited and 

 weighed. The precipitate can also be dissolved and treated with 

 uranium solution as described. 



The method used by Oliveri for basic slags may also be em- 

 ployed and it is carried out as indicated in the following descrip- 

 tion. SB 



A weighed quantity of the slag is reduced to a fine powder. 

 To five grams of the sample is added three times its weight of 

 34 Le Stazioni sperimentali agrarie italiane, 1891, 20 : 159. 



