JJ38 



was then prepared by mixing this filtrate with tlie required volume 

 of 9.6 7, solution of Na,HPO, 2 aq and KH^PO^. A row of Jena 

 test-tubes, each with 10 cc. of this liquid, was placed in the thermo- 

 stat together with a 250 or 500 cc. flask with a 0.12 "/, or a 0.06 V, 

 urea soiutioii, in short, the same methods were followed as described 

 above in the determination of the constant ii. 



Some preliminary experiments had shown, that w, as calculated 

 with our formula, was small at low and at high H-ion concen- 

 tration, and that two hours' standing at 27° was alieady somewhat 

 destructive to the enzyme in distinctly alkaline solution, not, however, 

 in acid ones. 



unless the acidity has been too high, the diminution of the urease- 

 activitv by acids is a reversible process, like the iieutralisation of a 

 basic substance. 



This fact was established by experiments, the particulars of which 

 will be omitted here for want of space. 



In Sept. 1916 the following series of experiments was made with 

 0.027, "I'ea. The correction for the traces of NH,, developed from 

 the materials employed, waS estimated in the ordinary way by col- 

 lecting these small quantities from 3 tubes, each with 10 cc. extract, 

 in the same absorbing tube with 5 cc. H,SO< 750 N. 



In order to meet the possible objection, that the enzyme might 

 have suffered by the influence of time, temperature and true reaction, 

 in both the last experiments a tube with 10 cc. of the same mixture 

 as contained in the other ones, was left for 4 hours in the bath 

 before introducing into it 2 cc. of urea solution. After 60 minutes 

 the same amount of urea was found to have been hydrolysed as 

 recorded in tables 10 and 11. As mentioned before and as will be 

 demonstrated more extensively further on, the stability of urease is 

 still greater at lower pff. 



These experiments already confirm the theory. At high H-ion 

 concentration the course of the reaction, as seen by comparison of 

 the last columns, is practically identical with that which can be 

 represented by the law of mass-action. The lower this concentration, 

 the more it deviates from it and approaches to a straight line, just 

 in the same degree, as predicted by the formula: 



lorj 1- ay 



0,434 ^ 1 



m = 



t 



By taking as the unit of urease concentration 1 gram of Soja 

 to 150 cc total 9.6 7o phosphate solution and reducing to this the 



