Apr. 15, 1920 Effect of Solution Reaction on Germination and Growth 75 



would be one which would permit a variation in unit steps over the 

 desired range and at the same time produce solutions of sufficient stability 

 to prevent small changes in the total amount of acid or base from seriously 

 affecting the reaction. In other words, the solution should have a " buffer " 

 nature. In the titration of strong acids with strong bases, a point is 

 reached, as neutrality is approached, at which further additions of small 

 increments of base produce voxy rapid decreases in the hydrogen-ion 

 concentration. This corresponds to a rapid rise in the voltage curve 

 obtained in the electrometric titration of such solutions. Any solution 

 selected within this region of rapid change is unsuited to work requiring 

 constancy of reaction, particularly when subject to possible small changes 

 in total acidity. With acids and bases of low dissociation this difficulty 

 is not so marked, changes of reaction being much less abrupt under 

 similar conditions.^ Such solutions are commonly said to possess a 

 buffer nature and are well adapted to work similar to that herein 

 reported. 



In series A the reaction was varied by adding HgCg and NaOH to 

 the successive cultures in amounts equivalent to the following volume- 

 molecular concentrations : 



Culture No. 



3 

 4 

 5 

 6 



7 



The reaction curve as determined by the hydrogen electrode for this 

 series is shown in figure i, A.^ It mil be noted that this solution pos- 

 sesses sufficient buffer action to prevent any rapid changes in reaction 

 with change in total content of acid and base. 



' For a more complete discussion of this subject see Hillebrand {lo). 



2 The measurenients of hydrogen-ion concentration were made by means of the gas chain and hydrogen 

 electrode, using the potentiometer system and measuring electromotive force to o.oooi volt. For electro- 

 metric titrations a special cell equipped with mechanical stirring device was designed. 



164176''— 20 3 



