804 EXPERIME-\'T STATION KECORD. 



velocity of the hydrolysis Is liulepeudent of the hydrogen or hydroxyl ion con- 

 centration within rather narrow limits. Hydrochloric acid or sodium hydroxld 

 in sufficient amounts inhibits the action of the enzym and also destroys it. 

 Ethyl alcohol exercises only a moderate inhibitory effect, and its destructive 

 action is apparently very sliglit." 



The mode of action of urease, D. D. Van Slyke, G. Zachabias, and G. E. 

 CuLLEN {Abs. in Proc. Soc. Expt. lUol. and Med., 11 (I'JUt), JVo. 5, p. 155). — 

 The all^allnity of the ammonium carbonate generated during the process ac- 

 counts for the retardation of urease activity. 



" When the solution is liept neutral by a proper phosphate mixture the prod- 

 ucts have no effect on the velocity of the reaction. Elimination of the effect 

 of the products maizes urease a particularly favorable enzym with which to 

 study the reaction between enzym and substrat. The results indicate that the 

 action consists of two successive reactions; combination of enzym and sub- 

 strat in definite proportions; and decomposition of the compound, the urea 

 being thrown off as ammoniuju carbonate ; each of the two reactions consuming 

 a definite portion of the total time. Formulation of these relations leads to 



the equation t= — lo"-^+4-- ^ repre.senting the time required for the decom- 



c '^ a—x ' a 



position of x amount of the initial substrat amount, « ; c is a constant repre- 

 senting the velocity of combination of enzym and substrat, d representing the 

 velocity of decomposition of the complex. The values of c and d can be de- 

 termined independently, and one can thereby determine whether changes in 

 conditions affect the combination reaction or that of decomposiiion. Neutral 

 salts retai'd the combination. Alkaline reaction hastens it, but retards the de- 

 composition. Slightly acid reaction greatly retards the combination, affecting 

 the other reaction but little. The independent variation of the two phases of 

 the process of enzym action explains some previously obscure facts in regard 

 to the effect of allialis, acids, and other substances on enzym action." 



The preparation of " neutral " ammonium citrate, E. D. Eastman and J. H. 

 HiLDEBRAND {JouT. ludus. mid Engiii. Chem., 6 {1914), A'O- 7, pp. 577-580, figs. 

 3). — Following a discussion of methods previously proposed by others for pre- 

 paring neutral ammonium citrate (PI S. R., 29, pp. 203, 718), it is announced 

 that with the aid of the hydrogen electrode '^ an indicator method has been 

 developed for the preparation of triammonium citrate. The hydrogen ion con- 

 centration given by a solution of this salt having a specific gravity of 1.09 is 

 lO"'*. " This concentration is obtained in the preparation of the citrate by 

 the use of an easily prepared color standard, made by mixing HCl and 

 Na2-HP04 solution. The results of a simultaneous determination of the 'neu- 

 tral point ' with the electrode and conductivity methods are shown graphically, 

 and there are given results of several trials of the formula suggested." 



The difficulties of the fertilizer chemist in determining the available phos- 

 phoric acid do not seem to be due entirely to the lack of uniformity of am- 

 monium citrate solution used. " It may be impossible to distinguish shari>ly 

 between 'reverted' and 'available' phosphate by means of neutral am- 

 monium citrate solution." 



Cause of error in the precipitation of ammonium-magnesium phosphate 

 in the presence of ammonium citrate, A. Quartaroli {Staz. Sper. Agr. Itah, 

 JfG {1913), No. 5, pp. 322-328). — It is believed by some that ammoniuni-jn.'ig- 

 nesium phosphate is not entirely insoluble in a strong solution of ammonia, and 

 that danger also exists of the i)recipitation of magnesium oxyeitrate. In these 

 investigations it is shown that when either ferric chlorid or aluminic chlorid 



".Tour. Amer. Chem. Soc, 35 (1913), Nos. 7, pp. 847-871, figs. 15; 10, p. 1538. 



