336 PHYSIOLOGICAL CfiEMlSTRY 



mination of urea in urine by the direct Nesslerization process 

 of Folin and Denis. By using urease preparations sufficiently 

 free from nitrogenous materials the urea nitrogen can be Ness- 

 lerized without any charcoal treatment. 



UREASE PREPARATION. Wash about 3 g. of permutit in a flask 

 once with 2% acetic acid, then twice with water; add 5 g. of 

 fine Jack bean meal and 100 c.c. of 15% alcohol (16 c.c. of 

 ordinary alcohol plus 84 c.c. of water). Shake gently but con- 

 tinuously for 10 to 15 minutes, pour on a large filter and cover 

 with a watch glass. The filtrate contains practically the whole 

 of the urease and extremely little of other materials. The urease 

 solution will keep for about a week at room temperatures and 

 for 4 to 6 weeks in an ice box. 



BUFFER MIXTURES FOR UREASE DECOMPOSITIONS. Mixtures of 

 mono- and disodium-phosphates in the proportion 1 molecule 

 of the former to 2 of the latter, and in molar concentrations, 

 are usually employed to preserve a substantially neutral reac- 

 tion during the decomposition of urea by means of urease. Dis- 

 solve 69 g. of monosodium phosphate and 179 g. of crystallized 

 disodium phosphate in 800 c.c. of warm distilled water. Cool 

 and dilute to a volume of 1 liter. 



It would seem to be rather doubtful whether the maintenance 

 of neutrality is adequate to fully explain the accelerating action 

 of phosphates on the urea decomposition, because pyro- and 

 metaphosphates seem to be more effective than orthophosphates. 

 An excellent buffer mixture is obtained by dissolving 14 g. of 

 sodium pyrophosphate (Na 4 P 2 7 , 10H 2 0) in enough half normal 

 phosphoric acid to make a volume of 100 c.c. The half normal 

 phosphoric acid is made by diluting 20 c.c. of 85% phosphoric 

 acid to 1 liter and titrating 5 c.c. with tenth normal alkali and 

 phenolphthalein as indicator to a faint pink color. On the 

 basis of this titration dilute the acid to a substantially correct 

 half normal solution. Metaphosphoric acid is fully as good as 

 phosphoric acid, but it is much more difficult to prepare a solu- 

 tion of the requisite degree of neutrality with metaphosphoric 

 acid because of its variable water and free phosphoric acid con- 



