744 



DR CHARLES HUNTER STEWART ON THE ESTIMATION OF 



into ammonia in the case of easily decomposed bodies, as uric acid, asparagin, and most 

 albuminoid substances. Most of the alkaloids and all the aromatic bodies give, by simple 

 heating with sulphuric acid, a much smaller percentage of their nitrogen as ammonia. 



When the reaction is ended, the flask is allowed to cool, and then the contents are 

 diluted with distilled water, emptied into a distilling flask, and made frankly alkaline 

 with a strong solution of caustic potash previously boiled and cooled. In the distillation 

 bumping must be avoided. 150 c.c. are distilled over and collected in an Erlenmyer 

 flask of 250 c.c. capacity, containing a measured quantity of ^\jth normal sulphuric acid. 

 This flask has a double-bored cork ; through one of the holes passes the delivering end 

 of the condenser about half-way in, in the other there is a glass tube cut flush with the 

 cork inside, and opening free to the outside. The titration is done by ^th normal 

 alkali, litmus being the indicator. 



The following are some of the results given by him, compared with results by Will 

 and Varrentrap's method. 





Kjeldahl's Method. 



Will and Varrentrap. 



Triethylamine, 



Asparagin, 



Uric acid, 



Urea, ..... 



Chloride of aniline, 











10' 16 per cent, nitrogen. 



18-7 



33*1 „ „ 



46-6 



1065 „ 



10-18 per 



18-67 



33-3 



46-7 



10-82 



cent, nitrogen. 

 > »» 



7 » 



Indigotin, .... 

 Hippuric acid, 

 Hydrochlorate of morphia, 

 „ „ quinine, 

 Caffein, 











106 



7-75 „ 

 4-21 „ 



7-47 „ 

 28-6 



10-68 



7-82 



436 



7-77 



28-86 



> J 

 } 1 

 1 ) 



y y 

 y y 





Casein, 











156 



15-6 



y y 





Egg albumen, 











15'3 „ „ 



15-6 



y } 





Many modifications of this process have been proposed, both for the purpose of 

 hastening the decomposition of the organic matter, and also for making it more generally 

 applicable. The more important among these are : (1) The addition of a small quantity of 

 phosphoric anhydride to the sulphuric acid. (This was first suggested by Kjeldahl 

 himself, but only in certain cases.) (2) The addition of about 0*5 gramme anhydrous 

 sulphate of copper and about 1 gramme metallic mercury. 



An elaborate investigation into this whole question was made by Dafert.* Regard- 

 ing the action of the sulphuric acid itself, he says (p. 329) : " The sulphuric acid 

 withdraws from the nitrogenous substance the elements of water and ammonia with the 

 formation of the latter." 



" The sulphurous acid formed during the decomposition acts in a reducing way on 



* Beitrcige zur Kentnisx den Kjeldahlschen Stickstoff-Bestimmungsverfahren ; Landwirthschaftlichen- Versuchs-Stationen, 

 Band xxxiv., 1887. 



