[Vol. 10 



330 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



sulphanilic acid, and a-naphthylamine-HCl) were then added to 

 the standards and 5-ml. portions of unknowns. One or more 

 drops of the respective reagents may be employed so long as the 

 amounts are constant for each test. The same concentration of 

 HC1 as given in the official method is obtained by diluting the 

 C.P. HC1 to one-tenth its strength. The solutions are allowed 

 to stand 30 minutes before the color comparisons are made. The 

 standards are made up fresh each time determinations are made. 

 Other comparable ratios for pipettes delivering other than 20 

 drops per ml. are readily calculated, and a volume other than 5 

 ml. may be chosen if the proper adjustments are made. The 

 advantages of the "micro" method are the ease of making quickly 

 a large number of standards, the economy in the use of reagents 

 and unknown solution, and the more accurate comparison of the 

 unknowns and standards by use of the comparator block and the 

 Duboscq colorimeter. Turbidity and color is compensated for 

 the same as in the hydrion determinations. 



Amino nitrogen determinations were made on the material 

 aerated in the NH a estimations by means of the van Slyke "mi- 

 cro" method in which 2 ml. of unknown solution were used. The 

 aeration removes NH 3 and free amides which would interfere, 

 giving abnormally large quantities of free N. Several preliminary 

 experiments showed that an interfering NH 4 salt may be separated 

 from an amino acid in this way. One of these experiments is 

 here given. Two 10-ml. samples of 0.1 N solution of (NH0»SO« 

 were added respectively to two 10-ml. quantities of an approxi- 

 mately 0.1 N alanine solution, 1 gm. K,CO» added, and the com- 

 bined solutions aerated for separation and determination of the 

 NH..N. Two 10-ml. samples of 0.1 JV (NH«) 2 SO« plus 1 gm. 

 KjCOi were aerated alone, as were 2 similar quantities of alanine 

 solution. Three 10-ml. portions of the (NH 4 ) 2 S0 4 solutions were 

 estimated by the Kjeldahl method, as were two 10-ml. aliquots of 

 alanine. 



