DUTCH JODLBAUER METHOD 375 



solving 50 grams of phenol in 100 cubic centimeters of strong 

 sulfuric acid. The combustion is continued until the solution is 

 colorless, which may take as much as five hours. If phosphoric 

 anhydrid be used the time of the combustion may be diminished 

 by one-half, but in such a case the glass of the combustion flask 

 is strongly attacked and is quite likely to break. 



When the substances used are very rich in nitrates, it is advis- 

 able to rub them first with dry gypsum. 



The theory of the process rests on the fact that by a careful 

 admixture of a nitrogenous substance diluted with land plaster 

 with phenolsulfuric acid, it is possible to change the nitric acid 

 into nitro-phenol, and by the reducing action of zinc dust to change 

 the nitro-product formed into amido-phenol. This afterwards 

 is transformed into ammonium sulfate by heating with sulfuric 

 acid, by which process, at the same time, all other nitrogenous 

 compounds present in the substance, as with Kjeldahl's method, 

 likewise form ammonium sulfate, only with the difference that 

 addition of mercury is here absolutely necessary for the com- 

 plete transformation of the slowly decomposed amido-phenol, 

 and this again brings about the necessity of decomposing the ni- 

 trogenous mercury compounds formed in the solution by potas- 

 sium sulfid, which is added after or with the soda-lye. 



325. The Dutch Jodlbauer Method. The Royal Experiment 

 Station of Holland directs that the jodlbauer process be carried 

 out as indicated below. 17 



The reagents necessary are: 



1. Phenolsulfuric acid, prepared by dissolving 100 grams of 

 pure crystallized phenol in pure sulfuric acid (1.84) and making 

 up the solution to a liter with the same sulfuric acid. 



2. Zinc, carefully washed and thoroughly dried. 



3. Sodium hydro.vid solution, the same as is used in the kjeld- 

 ahl method. 



4. Potassium sulfid solution, made by dissolving 355 grams of 

 potassium sulfid (K 2 S), or sodium sulfid solution, made by dis- 

 solving 250 grams of sodium sulfid (Na,S) in a liter of water. 



17 Methoden van Onderzoek aan de Rijkslandbowproefstations voor 

 het Jaar, 1894. 



