IJ FERTILIZERS 



with the condenser, mix the contents by shaking, distil until all ammonia has 



over into a measured quantity of the standard acid and titrate with the standard 



alkali. The first 150 cc. of the distillate will generally contain all the ammonia. 



The use of mercuric oxid in this operation greatly shortens the time necessary 

 for digestion, which is rarely over an hour and a half in case of substances most 

 difficult to oxidize, and is more commonly less than an hour. In most instances 

 the use of potassium permanganate is quite unnecessary, but it is believed that in 

 exceptional cases it is required for complete oxidation, and in view of the uncer- 

 tainty it is always used. The potassium sulphid removes all the mercurj"- from the 

 solution, and so prevents the formation of mercuro-ammoniura compounds which 

 are not completely decomposed by the sodium hydroxid. The addition of zinc 

 gives rise to an evolution of hydrogen and prevents violent bumping. 



Previous to use the reagents should be tested by a blank experiment with sugar. 

 The sugar partially reduces any nitrates present that might otherwise escape notice. 



Gunning Method. — Official. 



19 REAGENTS. 



Potassium sulphate. — Pulverized. 



The other reagents and standard solutions used are described under 16. 



20 APPARATUS. 



The apparatus used is described under 17. 



21 DETERMINATION. 



Place 0.7-3.5 grams, according to the nitrogen content, of the substance to be 

 analyzed in a digestion flask. Add 10 grams of powdered potassium sulphate and 

 15-25 cc. (ordinarily about 20 cc.) of sulphuric acid (0.1-0.3 gram of crystallized 

 copper sulphate may also be added). Conduct the digestion as in the Kjeldahl 

 process, starting with a temperature below the boiling point and increasing the heat 

 gradually until frothing ceases. Digest for a time after the mixture is colorless or 

 nearly so, or until oxidation is complete. Do not add either potassium permanganate 

 or potassium sulphid. Cool, dilute, neutralize, distil, and titrate with the standard 

 alkali. In neutralizing before distilling it is convenient to add a few drops of 

 phenolphthalein indicator or litmus paper. The pink color given by phenolphthal- 

 ein indicating an alkaline reaction is destroj-ed by a considerable excess of strong 

 fixed alkali. 



Kjeldahl-Gunning -Arnold Method. — Official. 



22 REAGENTS AND APPARATUS. 



Described under 16, 17 and 19. 



DETERMINATION. 



23 



Place 0.7-3.5 grams, according to the nitrogen content, of the substance to be 

 analyzed in a digestion flask. Add 15-18 grams of potassium sulphate, 1 gram of 

 copper sulphate, 1 gram of mercuric oxid, or its equivalent in metallic mercury, 

 and 25 cc. of sulphuric acid. Heat gently until frothing ceases, then boil the mixture 

 briskly, and continue the digestion for a time after the mixture is colorless or nearly 

 so or until oxidation is complete. Cool, dilute with about 200 cc. of water, add 50 cc. 

 of potassium sulphid sqlution, make strongly alkaline with sodium hydroxid solu- 

 tion and complete the determination as directed under 18. 



