138 MANUFACTURE OF FERTILIZING MATERIALS 



ignited and weighed by some, and half its weight 

 taken as that of the iron alumina oxide, which 

 roughly speaking is true. It is, however, more 

 exact and satisfactory to dissolve the moist, 

 hydrates in nitric acid, neutralize closely, pre- 

 cipitate out phosphoric acid with a sufficient 

 but not too large excess of ammonium molyb- 

 date, letting it stand warm for some hours, 

 and in the filtrate precipitate with ammonia, 

 boiling out the excess to render the alumina 

 insoluble. Filter, and then treat the precipitate 

 with about 10 cc. of strong ammonia to dissolve 

 out the molybdic acid, wash again, and dry, 

 ignite, and weigh the mixed oxides. 



If desired, the precipitate may be brought 

 into solution, and the iron reduced and titrated 

 in the usual manner, the alumina being obtained 

 by difference. 



