464 AGRICULTURAL ANALYSIS 



boiling water for 6 hours. Disulfonic instead of monosulfonic 

 acid is thus produced by the prolonged high temperature, and 

 this reacts readily upon the nitrate. 



Standard potassium nitrate prepared as described above. 



397. Variation of Johnson. The ammonium picrate method 

 has given very satisfactory results as practiced by Johnson, who 

 varies the process as described below: 83 



The standard solution of potassium nitrate is prepared by dis- 

 solving 0.7215 gram of the pure salt in a liter of distilled water, 

 and diluting 100 cubic centimeters of this solution to one liter 

 with distilled water. Ten cubic centimeters of this dilute solu- 

 tion contain nitrogen equivalent to one part as nitrates in 100,000. 



The Solution of Acid Phenyl Sulfate. This is prepared by 

 pouring two parts, by measure, of pure crystallized phenol lique- 

 fied by hot water into five parts, by measure, of pure concentrated 

 sulfuric acid and digesting in the water-bath for eight hours. 

 After cooling, add one and one-half volumes of distilled water and 

 one-half volume of strong hydrochloric acid to each volume of 

 the above mixture. 



The analytical processes are carried on as follows: Ten cubic 

 centimeters of the sample or extract under examination and 10 

 cubic centimeters of the standard potassium nitrate are placed in 

 small beakers and put near the edge of a hot plate. When nearly 

 evaporated they are put on the top of the water-bath and left 

 there until completely dry. The residue, in each case, is treated 

 with one cubic centimeter of the acid phenyl sulfate and the 

 beakers placed on the top of the water-bath. In an extract very 

 poor in nitric acid a red color ought not to appear for about 10 

 minutes. 



After standing about 15 minutes, the beakers are removed, 

 and the contents of each washed successively into 100 cubic centi- 

 meter flasks ; about 20 cubic centimeters of 0.96 per cent, ammo- 

 nia are then added, the 100 cubic centimeters made up by the 

 addition of water, the yellow liquid transferred to the nessler 

 glass and the tints appropriately compared. 



M Chemical News, 1890, 61 : 15. 



