MODIFICATIONS OF ASBOTH 373 



ing from 250 to 550 cubic centimeters, place from 0.7 to 3.5 

 grams of the substance to be analyzed, according to its propor- 

 tion of nitrogen. Add 10 grams of powdered potassium sulfate 

 and from 15 to 25 cubic centimeters (ordinarily about 20 cubic 

 centimeters) of concentrated sulfuric acid. Conduct the diges- 

 tion as in the kjeldahl process, starting with a temperature be- 

 low boiling-point and increasing the heat gradually until all froth- 

 ing ceases. Digest until colorless or nearly so. Do not add either 

 potassium permanganate or potassium sulfid. Dilute, neutralize, 

 and distil as in the kjeldahl method. In neutralizing, it is conven- 

 ient to add a few drops of phenolphthalein indicator, by which one 

 can tell when the acid is completely neutralized, remembering 

 that the pink color, which indicates an alkaline reaction, is de- 

 stroyed by a considerable excess of strong fixed alkali. The dis- 

 tillation and titration are conducted as in the kjeldahl method. 

 In distilling, the use of zinc or of some substance to prevent 

 bumping or foaming is generally necessary. The amount of sul- 

 furic acid recommended by Gunning is two grams for each gram 

 of potassium sulfate ; but Van Slyke has found that this mixture 

 is so viscous as to cause troublesome foaming frequently, and 

 after cooling it cakes in a hard mass, which may be difficult to 

 redissolve. 14 To avoid foaming and caking, he has found it an 

 effective means to increase the amount of sulfuric acid used, 

 using instead of two grams to one of potassium sulfate, three or 

 four grams of acid to one of potassium sulfate. It is, therefore, 

 suggested in carrying out the work, to use from five to 25 cubic 

 centimeters (ordinarily about 20 cubic centimeters) of sulfuric 

 acid for 10 grams of potassium sulfate. In case the potassium 

 sulfate is not free from nitrogen compounds, one or two recrys- 

 tallizations will make it pure. 



CHANGES IN KJELDAHL METHOD TO INCLUDE NITRIC ACID 



323. Modifications of Asboth. In order to adapt the moist 



combustion process to nitric nitrogen Asboth proposed the use of 



benzoic acid. 15 For half a gram of saltpeter 1.75 grams of ben- 



u Division of Chemistry, Bulletin 35, 1892 : 68. 



15 Chemisches Central-Blatt, 1886 : 161. 



