268 Stiggestions to Teachers of Biochemistry [Dec. 



fact that colorless (reduced) Pavy reagent is a very affective Sub- 

 stitute for the biuret reagent in the biuret test. Each of many tests 

 confirmed this finding. The tendency to prompt restoration of the 

 blue color, unless we devise means of preventing it, makes it neces- 

 sary to prepare fresh portions of this colorless reagent frequently 

 for its satisfactory general employment. 



The biuret reagent itself is easily reduced to a practically color- 

 less condition by heating it with a proper amount of very dilute 

 glucose Solution, but cuprous oxid may then be seen in it. If, 

 however, the biuret reagent is rendered ammoniacal and then 

 cautiously reduced to the colorless condition with dilute glucose 

 Solution, the resultant colorless liquid is free from cuprous oxid 

 and with it protein gives the biuret test beautifully. The keeping 

 qualities of the decolorized biuret reagent are better than those of 

 the reduced Pavy reagent, evidently because of the lower concen- 

 tration of copper in the former. 



These observations naturally led to the trial of an " alkaline 

 reducing agent." Zinc dust, the only reducing agent of this kind 

 that it has been convenient to try thus far, promptly reduces the 

 biuret reagent to the colorless condition. In this State the reagent 

 produces the biuret coloration in a protein Solution but the reagent 

 is less effective than before its decolorization. Many more experi- 

 ments than the few we have been able to find time to conduct will 

 be required, in connection with methods of reduction, before we 

 shall be satisfied that a permanently colorless, perfectly satisfactory, 

 biuret reagent cannot be prepared by such means. 



Thus far the most satisfactory attempts to prepare a colorless 

 biuret reagent have depended upon ( i ) the Solution of cuprous oxid 

 in ammonium hydroxid Solution under conditions that prevent oxi- 

 dation, and (2) the addition of caustic alkali to this colorless am- 

 moniacal Solution in sufficient proportion to accomplish effective 

 disOrganization of protein for the maximum production of typical 

 biuret coloration. We hope to extend these particular experiments, 

 and others collateral to them, at an early opportunity. 



The Chief difficulties in the way of satisfactory preparation of a 

 colorless biuret reagent have been (i) the persistent tendency of the 

 colorless ammoniacal reagents to acquire color spontaneously or 



