374 AGRICULTURAL ANALYSIS 



zoic acid should be used. At the end of the combustion the re- 

 sidual benzoic acid is oxidized by means of potassium perman- 

 ganate with a subsequent reheating. If the nitrogen be present 

 as an oxid or as cyanid, one gram of sugar is added. The me- 

 tallic element added is half a gram of copper oxid. Asboth also 

 recommends that the soda-lye used in the distillation be mixed 

 with sodium potassium tartrate for the purpose of holding the 

 copper and manganese oxids in solution and thus preventing 

 bumping. The alkaline liquor contains in one liter 350 grams 

 of the double tartrate and 300 grams of sodium hydroxid. 



The principle on which the use of benzoic acid rests is found 

 in the fact that it easily yields nitro-compounds and thus pre- 

 vents the loss of the nitrogen oxids, these readily combining 

 with the benzoic acid. The nitro-compounds can be subsequently 

 converted into ammonia by treatment with potassium perman- 

 ganate. 



The pyridin and chinolin groups of bodies do not yield all their 

 nitrogen as ammonia by the above treatment. 



The conclusions drawn by Asboth from the analytical data ob- 

 tained are: 



(1) Sugar should be used in the ordinary kjeldahl process in 

 those cases where the nitrogen in the organic substance is pres- 

 ent as oxids or as cyanogen. 



(2) In the case of nitrates good results may be secured with 

 benzoic acid but permanganate must be added at the end. 



(3) The kjeldahl-wilfarth process can be applied with sub- 

 stances difficultly decomposed, e. g., alkaloidal bodies. 



324. Variation of Jodlbauer. The benzoic acid method, al- 

 though a step forward, is not entirely satisfactory in the treat- 

 ment of nitrates by moist combustion. Jodlbauer has proposed to 

 substitute for the benzoic, phenolsulfuric acid. 10 



From two- to five-tenths gram of a nitrate are treated with 

 20 cubic centimeters of concentrated sulfuric and two and a 

 half of phenolsulfuric acid, together with three grams of zinc 

 dust and five drops of a solution of platinic chlorid of the strength 

 mentioned above. The phenolsulfuric acid is prepared by dis- 

 18 Chemisches Central-Blatt, 1886 : 433. 



