156 The Phosphates of America. 



less filter, washed as in the case of raw phosphates, dried, calcined 

 in a porcelain crucible and weighed as Mg 2 P 2 O 7 . The weight of 

 the residue X .6396 X 2 = the water-soluble phosphoric anhydride 

 in one gramme of the superphosphate. 



Citrate-insoluble Phosphoric Anhydride. 



The residue from the treatment with water is washed into a 

 200-c.c. flask, with 100 c.c. of strictly neutral ammonium citrate 

 solution of density 1.09. The flask is securely corked and placed 

 in a water-bath, the water of which stands at 65 C. (The water- 

 bath should be of such a size that the introduction of the cold 

 flask may not cause a reduction of the temperature of the bath of 

 more than 2 C.) 



The temperature of 65 C. is maintained for thirty minutes, with 

 vigorous shaking of the flask every five minutes. The warm solu- 

 tion in the flask is then filtered quickly and washed with water of 

 ordinary temperature. The filter is transferred, with its contents,, 

 to a capsule, and ignited until the organic matter is destroyed. It 

 is then treated with 10 to 15 c.c. of concentrated hydrochloric acid ;. 

 digested over a low flame until the phosphate is dissolved ; diluted 

 to 200 c.c. mixed, and passed through a dry filter. One hundred 

 c.c. of it are nearly neutralized with ammonia ; 10 grammes of 

 ammonium nitrate are added ; the liquid is made quite warm and 

 there are then added to it 150 c.c. molybdic solution. The process 

 is completed exactly the same way as with raw phosphates. 



The weight of the Mg 2 P 2 O 7 X .6396 X 2 -=- 5 equals the citrate- 

 insoluble phosphoric anhydride in one gramme of the substance. 



Total Phosphoric Anhydride. 



Two grammes of the superphosphate are weighed with great 

 accuracy and treated in a porcelain capsule with 30 c.c. concen- 

 trated hydrochloric acid. Heat is applied and there is added cau- 

 tiously, and in small quantities at a time, about .5 gramme of 

 finely-pulverized potassium chlorate. 



The mixture is gently boiled until all phosphates are dissolved 

 and all organic matter destroyed, and is then diluted to 200 c.c.,. 

 mixed and passed through a dry filter. Fifty c.c. of filtrate 

 equal to half a gramme of the superphosphate are then taken and 

 neutralized with ammonia, and about 15 grammes of dry am- 

 monium nitrate are added. The solution is now made warm ; 150- 

 c.c. molybdic solution are added, and thenceforward the process 

 is conducted exactly as in the case of raw phosphates. 



