54 AGRICULTURAL ANALYSIS 



61. Official Method. The official chemists recommend seven 

 methods of solution for mineral phosphates, phosphatic materials 

 and preparations thereof; viz., 28 



1. Ignite and dissolve in hydrochloric acid. 



2. Evaporate with five cubic centimeters of magnesium nitrate 

 solution and dissolve in hydrochloric acid. This method is ap- 

 plicable in the presence of organic matter. 



3. Boil with from 20 to 30 cubic centimeters of strong sulfuric 

 acid, adding from two to four grams of sodium or potassium 

 nitrate at the beginning of the digestion and a small quantity, 

 after the solution has become nearly colorless. Or the nitrate in 

 small quantities may be added at regular intervals during the 

 whole time of the digestion, which is conducted in a kjeldahl 

 flask marked at 250 cubic centimeters. When the solution is 

 colorless add 150 cubic centimeters of water, boil for a few 

 minutes, cool and make up to the mark with water. 



4. Digest with strong sulfuric acid and such other reagents as 

 are used in the processes for converting nitrogen in nitrogenous 

 compounds into sulfate of ammonia as described in the second part 

 of this volume. Do not add any potassium permanganate but 

 after the solution has become colorless add about 100 cubic centi- 

 meters of water, boil for a few minutes, cool and make up to a 

 convenient volume (250 cubic centimeters). The operation should 

 be conducted on about 2.5 grams of substance. 



Processes 3 and 4 are especially applicable to organic sub- 

 stances such as oil cakes, which contain considerable quantities 

 of phosphorus. 



5. Dissolve in 30 cubic centimeters of concentrated nitric and a 

 small quantity of hydrochloric acid and boil until organic matter 

 is destroyed. 



6. Add to the substance 30 cubic centimeters of concentrated 

 hydrochloric acid, heat and add cautiously in small quantities at 

 a time about 0.5 gram of finely pulverized potassium chlorate to 

 destroy organic matter. 



7. Dissolve the substance in from 15 to 30 cubic centimeters of 

 strong hydrochloric acid and from three to 10 cubic centimeters 



w Bureau of Chemistry, Bulletin 107, 1907 : 2. 



