OFFICIAL METHODS OF BELGIUM AND HOLLAND. 305 



until evolution of gas commences. The flame is then removed until 

 the evolution subsides. Finally the flask is heated gently for about 

 5 minutes. One hundred cubic centimeters of distilled water is added 

 and the ammonia distilled oft' in the presence of 3 gm. of calcined mag- 

 nesia or of 30 cc. of a soda solution of 1.25 sp. gr. 



Organic nitrogen. — Two methods of determining organic nitrogen are 

 employed, the Kjeldahl and the modified Gunning methods. In the 

 first 1 gm. of blood or horn, U gm. of leather, wool, oil cake, or fish 

 guano, and 2 gm. of ground bone is digested with 10 to 20 cc. of sul- 

 phuric acid of 66° Baume, containing 10 per cent of phosphoric anhy- 

 drid and a drop of mercury (about 0.5 gm.) or from 0.5 to 1 gm. of mer- 

 cury bioxid. The digestion is continued at least 1 hour after the 

 solution has become colorless. After cooling the solution is nearly 

 neutralized with potash solution (1 part of potash to 2 of water), and 

 then 40 cc. of a solution containing 50 gm. of caustic soda and 20 gm. 

 of sodium sulphid per liter is added. The operation is continued in 

 the usual way. 



In the modified Gunning method the same weights of material are 

 used, the substance being digested in 20 cc. of 6G° Baume sulphuric 

 acid with the addition of 1 gm. of mercury and 1 gm. of copper sul- 

 phate. When the substance has become charred 10 to 15 gm. of potas- 

 sium sulphate in crystals is added and the mixture strongly heated. 

 Digestion is complete in about half an hour. The operation is com- 

 pleted as in the Kjeldahl method. 



With fertilizers containing a mixture of nitric and ammoniacal nitro- 

 gen 10 gm. is dissolved in 500 cc. of water and 25 or 50 cc. of the solu- 

 tion used for the different determinations, nitric nitrogen being deter- 

 mined by the Schloesing-Grandeau method, ammoniacal nitrogen by 

 distillation with magnesia. 



With fertilizers containing organic and ammoniacal nitrogen the total 

 nitrogen is determined in 2 gm. by the Kjeldahl method, ammoniacal 

 nitrogen in 5 gm. by distillation with magnesia. 



With fertilizers containing organic and nitric nitrogen the total nitro- 

 gen is determined in 1 to 2 gm. by the Kjeldahl-Jodlbauer method as 

 follows: Digest the fertilizer in 20 to 30 cc. of sulpho-phenic acid con- 

 taining from GO to 100 gm. of crystallized pbenic acid per liter. For 

 hastening solution it is recommended to heat slowly to about 10° C, 

 cool and add 1 gm. of zinc powder in small portions, digest in the cold 

 for at least 2 hours, then proceed as in the ordinary Kjeldahl method. 

 The nitric nitrogen is determined by the Schloesing-Grandeau method. 



•In fertilizers containing the 3 forms of nitrogen the total nitrogen is 

 determined by the Kjeldahl-Jodlbauer method, ammoniacal nitrogen 

 by distillation with magnesia, and nitric nitrogen by the Schloesing- 

 Grandeau method. 



Phosphoric acid soluble in mineral acids. — To 50 gm. of the phosphate 

 add 50 cc. of nitric acid (1.2 sp. gr.) or aqua regia and 50 cc.of water. Boil 



