1914] Anton R. Rose and Katherine R. Coleman 413 



As a result of this study, two procedures have been adopted in 

 this laboratory.* 



I. The micro-urease method is used in determining urea in 

 small samples or when the amount of this substance is present in 

 only minute quantities. Into a 22 X 200 mm. test tube, the Solu- 

 tion to be analyzed is carefully pipetted in an amount not exceeding 

 5 c.c, and containing not more than 2 mg. of nitrogen in the form 

 of ammonia and urea. When only i c.c. is used, 2 c.c. of water 

 are also added. If the Solution is acid, it should be neutralized. 

 Then 0.2-0.4 grn. of the bean flour is added and the mixture stirred, 

 0.5 c.c. of amyl or octyl alcohol run in, the tube attached to the 

 apparatus, and aeration started. Under the tubes is placed a nar- 

 row pan into v/hich is poured some water warmed to 50-60° C. 

 In 5 min. the reaction is complete. To facilitate the removal of 

 ammonia, 1-2 c.c. of saturated sodium carbonate sol. is drawn into 

 the tube. The time of aspiration under the conditions prevailing in 

 our laboratory need not exceed 35 min. 



[The experience of this laboratory, as to the time required for 

 the removal of the ammonia from a Solution by aeration in micro 

 and macro determinations of nitrogen and ammonia, does not agree 

 with the published Statements of Folin and his co-workers. In the 

 latter six hours are usually required and in the former not less than 

 thirty minutes. Sjoquist^ presents data in harmony with this and 

 also notes that the time may be materially shortened by warming the 

 Solutions. These variable time requirements are due to local con- 

 ditions and should be tested in each laboratory where the methods 

 are used.] 



The receiving pipette is removed, the acid previously placed in 

 it diluted to about 75 c.c, Nessler reagent added and then, after 

 mixing, made up to the mark and matched against the appropriate 

 platinum Standard in the Duboscq colorimeter or titrated with w/50 

 Solutions. From these readings is subtracted the readings previously 

 obtained for ammonia nitrogen, and the urea nitrogen calculated. 



When the nitrogen of the sample taken is less than 0.4 mg., it is 



*A paper by Plimmer and Skelton in a recent issue of the Bicochemical 

 Journal (viii, p. 70) is in dose agreement with the subject matter treated in 

 this paper. 



6 Sjoquist: Sv. Kern. Tidskr, 1913, xxv, p. 167. Cf. C. A., 1914, viii, p. 743- 



