3/6 AGRICULTURAL ANALYSIS 



Oxidation flasks holding about 200 cubic centimeters, and dis- 

 tillation flasks holding about 750 cubic centimeters, both of Bo- 

 hemian glass are used. 



Manipulation. Moisten one gram of substance with water, dry 

 and introduce into an oxidation flask. Cover with 15 cubic cen- 

 timeters of phenolsulfuric acid and, after cooling, thoroughly mix 

 by gently shaking. After five minutes add from two to three 

 grams of zinc in small proportions, keeping the flask cool, then 20 

 cubic centimeters of sulfuric acid, and finally two" drops of 

 mercury. Boil the mixture till the fluid is colorless, cool and 

 dilute. Wash into a distillation flask and add an excess of sodium 

 hydroxid solution and 25 cubic centimeters of the sodium (or 

 potassium) sulfid solution. Distil and titrate as in the kjeldahl 

 method. 



326. The Halle-Jodlbauer Method. At the Halle Station it is 

 the uniform practice to mix the nitrate with gypsum before 

 the combustion. 18 In the case of Chile nitrates 10 grams 

 are rubbed with an equal amount of gypsum, and two grams of 

 the mixture, equal to one gram of the nitrate, used for the 

 determination. In the case of saltpeter mixtures which contain 

 over eight per cent, of nitrogen, one gram of the mixture with 

 gypsum is used, of guanos one and a half grams, and of lower 

 forms of nitrates or mixtures thereof, from three to five grams. 



The sample, as prepared above, is treated with 30 cubic centi- 

 meters of a mixture of phenolsulfuric acid and phosphoric 

 anhydrid. The mixture is prepared by dissolving 66 grams of 

 phenol and 250 grams of phosphoric anhydrid in strong sulfuric 

 acid, and, after cooling, mixing the two solutions and making 

 the volume up to 1650 cubic centimeters with pure sulfuric acid. 

 The mixture contains, in 30 cubic centimeters, one and two-tenths 

 grams of phenol and four grams of phosphoric anhydrid. In the 

 use of phenolsulfuric acid the presence of phosphoric anhydrid 

 is indispensable in keeping the sulfuric acid water-free and in 

 absorbing the water produced by the combustion. 



18 Bieler und Schneidewind, Die agricultur-chemische Versuchsstation 

 Halle a/S, 1892 : 34. 



