Nitrogen Determinations by Direct

All methods for the determination of urea in urine dependent on purely chemical processes for the hydrolysis of the urea are apparently destined to become antiquated, if not forgotten, because of the abundant supply of urease now available for such hydrolysis. It would be easy to devise an excellent direct Nesslerization method for the determination of urea in urine on the basis of the Folin-Pettibone process, in which the urea is decomposed by the help of phosphoric acid and heat; but, recognizing the superiority of urease for the hydrolysis of urea we decided first to see whether a combination of direct Nesslerization with a urease decomposition of the urea could be obtained. The starting point of our research was the idea that ?n-phosphoric acid, which we had found so effective for the removal of blood proteins, might be used to remove from urine the urease materials added for the hydrolysis of the urea, and should thus yield filtrates suitable for direct Nesslerization. The out,come proved to be quite in accordance with our expectations and the remainder of the research has consequently been only a matter of deciding certain minor details in the practical application of the method to urine. Concerning these details there is much room for choice and individual preference. Since the added urease-containing material is removed before Nesslerization of the ammonia, it makes no difference within rather wide limits whether much or little of the material is used, or whether the ferment is added in the form of a concentrated enzyme powder, or as crude soy bean flour suspension. 501