148 MANUFACTURE OF FERTILIZING MATERIALS 



point for half an hour to complete the destruc- 

 tion of organic matter. At the end of this time 

 five grams of ammonium nitrate are added to 

 facilitate the precipitation of the phosphoric 

 acid, and 50 cc. of molybdate solution, and the 

 mixture kept at a temperature of about 100 C. 

 for an hour. The precipitate obtained is washed 

 twice by decantation with water containing 

 one-fifth of its volume of ammonium molybdate 

 solution. It is dissolved in 30 cc. of ammonia 

 diluted with an equal bulk of warm water. The 

 solution and washings should measure 80 cc. 

 and the ammonia therein is neutralized with 

 nitric acid, keeping the temperature below 40 C. 

 When the yellow precipitate formed ceases to 

 redissolve on stirring, that is, when the ammonia 

 has been neutralized, a mixture of 3 cc. of 

 pure nitric acid and 5 cc. of water is added, 

 together with the same quantity of molybdate 

 solution. After standing for two hours at 40 C. 

 the precipitate is brought upon a filter, washed 

 first with water containing 1 per cent of nitric 

 acid, and finally with a little pure water, and 

 dried at 100 C. and weighed. The weight of 

 the precipitate multiplied by the factor 0.0373 

 gives the quantity of phosphoric acid. The 

 object of the second precipitation is to relieve the 

 process of the necessity of rendering the silica 

 insoluble, as the presence of silica in the solu- 

 tion as above treated does not interfere with 

 the complete precipitation of the phosphate. 



