DETERMINATION OF AMINOACIDS 121 



If the solution be carefully neutralized before its trans- 

 formation with formaldehyde, the masking of the basic NH 2 

 groups becomes evident at once by the development of an 

 acid reaction ; and as a matter of fact this increase of acidity 

 after addition of f ormol, which may be determined by titra- 

 tion, is a precise measure of the amount of amino groups 

 present. It cannot be questioned that the method, the 

 technique of which has received much criticism and has been 

 improved in a number of ways, is really a valuable addition 

 to our scientific equipment. 73 



78 V. Henriques and S. P. L. Sorensen, Zeitschr. f . physiol. Chem., 6$, 27, 

 1909; 64, 120, 1910; V. Henriques, ibid., 60, 1, 1909; S. P. L. Sorensen, 

 Biochem. Zeitschr., 25, 1, 1910; H. Malfatti, Zeitschr. f. physiol. Chem., 61, 

 499, 1909; 66, 152, 1910; L. de Jager, ibid., 65, 185, 1910; 67, 1, 105, 1910; W. 

 Frey and A. Gigon, Biochem. Zeitschr., 22, 309, 1909; T. Yoshida, ibid., 23, 239, 

 1909; ef. also Neubauer-Huppert's Analyse des Harnes, 2d ed., article by A. 

 Ellinger, 1, 641 to 647, 1910; Neuberg, Der Harn., article by A. C. Andersen, 

 1, 569-630, 1911. 



