358 AGRICULTURAL ANALYSIS 



4. Paraffin in small pieces. 



5. Dilute sulfuric acid and dilute potash solution, both of known 

 strength. 



6. Pieces of previously ignited pumice stone or of granulated 

 zinc. 



7. Neutral solution of rosolic acid or litmus. 



Apparatus. The necessary apparatus consists of oxidation 

 flasks of about 200 cubic centimeters capacity and distillation 

 flasks of about 500 cubic centimeters capacity, both of Bohemian 

 glass. Copper may be used for the distillation flasks. 



The Process. A gram of the sample to be analyzed is placed 

 in an oxidation flask, together with 20 cubic centimeters of phos- 

 phosulfuric acid and a drop of mercury (about 600 milligrams), 

 and heated till the fluid becomes colorless. After cooling, dilute 

 and wash the contents of the flask into a distillation flask. The 

 resulting volume should be about 300 cubic centimeters. Add 

 loo cubic centimeters of the alkaline sodium sudfid solution and 

 some pieces of ignited pumice stone or granulated zinc. Distil 

 the ammonia, receiving the distillate in a flask containing a known 

 volume of the standard sulfuric acid. Titrate with tenth-normal 

 potash, using litmus or rosolic acid as indicator. 



315. The Kjeldahl Method as Practiced at the Halle Station. 

 The method in vogue in the German stations of conducting 

 the moist combustion process is well illustrated by the 

 method of procedure followed at Halle. 6 From 0.7 to 1.5 

 grams of the sample are used for analysis, according to its rich- 

 ness in nitrogen. Because of the fact that so small a quantity 

 of the sample is used, it is of the highest importance that it be 

 perfectly homogeneous throughout its entire mass. Otherwise, 

 grave errors may arise. From the sample as sent to the labo- 

 ratory the analyst should remove a subsample, and this should be 

 rubbed to a fine powder and the part used for analysis carefully 

 selected therefrom. If the sample be moist it may be rubbed up 

 with an equal weight of gypsum, in which case a double quantity 

 is employed for the determination. Substances like bone-meal, 



6 Bieler und Schneidewind, Die agricultur-chemische Versuchsstation 

 Halle a/S., 1892 : 34. 



