The Phosphates of America. 151 



and allowed to stand in a cool place until perfectly cold. It is then 

 filtered on an ashless filter and the beaker and residue are carefully 

 washed twice with boiling water. The flask containing the filtrate 

 is then removed from beneath the funnel and replaced by the 

 beaker in which the first precipitation was made. The substance 

 on the filter is now carefully dissolved in a little hot, fifty-per-cent. 

 solution of hydrochloric acid, and the filter is washed twice with 

 Lot water. The filtrate in the beaker is next made alkaline with 

 ammonia in slight excess ; then made strongly acid with pure con- 

 centrated acetic acid ; well stirred up, and again allowed to stand 

 until absolutely cold. The flask containing the first filtrate is now 

 replaced under the funnel, the liquid in the beaker is filtered 

 into it, the filter is washed twice with cold water containing a 

 little acetic acid, and then three times with boiling distilled water. 

 The funnel containing the filter is now placed in the oven and com- 

 ompletely dried, after which the filter and its contents are cal- 

 cined, and weighed as phosphates of iron and alumina in one 

 gramme of the material. For all the general purposes of the 

 factory, or for the control of daily work at the mines, it is 

 only necessary to divide the figure thus found by 2, and to state 

 the result roughly as "oxides of iron and alumina (combined)." 

 As we have given our reasons for this proceeding in an earlier part 

 of this chapter, it is not necessary to repeat them, and we will con- 

 tent ourselves with a mere example. 



The weight of the combined phosphates in one gramme was .058 ; 

 then .058 -f- 2 = .029 = 2.90 per cent, oxides of iron and alumina 



When reporting upon a sample for commercial purposes 

 that is to say, when determining its value to the manufacturer 

 of water-soluble superphosphates, it is sometimes necessary to 

 carry this analysis a little further. In such cases, after carefully 

 noting the accurate weight of the combined phosphates, they are 

 dissolved in boiling hydrochloric acid. The solution is filtered 

 into a 100-c.c. flask and washed up to the mark with boiling water. 

 No residue should remain on the filter save perhaps a speck or two 

 of carbon resulting from, the recent incineration. In one half of 

 the filtrate, the phosphoric anhydride is determined by the molyb- 

 date method already described. The resulting Mg 2 P 2 O 7 X .6396 X 2 

 equals the P 2 O 5 in one gramme of the combined phosphates. 



The remaining half of the filtrate is boiled with a small piece 

 of zinc in a flask fitted with a Bunsen valve. When the iron is com- 

 pletely reduced and gives no trace of pink coloration with potas- 



