114 THE ROLK OF NITROGEN IN PLANT-METABOLISM, iii., 



acid used. Secondly, the titrations, after distilling for four 

 hours, are still yielding nuich ammonia, and, no doubt, 

 would have continued for many hours longer, so that even 

 the last result of 31% is not at all the maximum figure 

 obtainable. 



Thirdly, the ammonia which distils is not all preformed in 

 the solution ; after the first hour, all preformed ammonia 

 must have been evolved, and the solution, by the continued 

 boiling with magnesia, still liberates ammonia slowly, and 

 in gradually lessening quantity. This is not characteristic 

 either of amides or amino-acids. 



However, the residual fluids in the distillation flasks were 

 now examined for compounds possessing the amino-group. 

 The apparatus for the nitrous acid method of Sachsse was 

 used as in a former operation. In the majority of these 

 determinations, no nitrogen was evolved. In a few, a small 

 amount only was obtained, which would account for less 

 than 0-5% of the non-protein nitrogen. 



The same residual fluids, after distillation with magnesia, 

 were next submitted to the Sorensen* titration. 



In this, the solution is titrated with one-fifth normal 

 sodium hydroxide, before and after treatment with neutral 

 formaldehyde. In the first stage, free acid and also those 

 carboxyl groups which are distant from an amino-group are 

 neutralised ; and, in the second stage, the formaldehyde 

 removes the amino-group, and with it disappears the pro- 

 tective influence of the latter on the a carboxyl-group, there- 

 by making the carboxyl-group available in the second 

 titration. 



Results. — Solutions a, h, c, d , e, when titrated, were 

 found to be neutral. After addition of the formaldehyde 

 solution, they still remained neutral. From these results 

 we should conclude that compounds containing the amino- 

 group were absent. 



»Biochem. Zeitsch. 7, 1907, s.45. 



