The Estimation of Acidity. 



249 



generally used in this laboratory. It has been shown by Has- 

 selbalch that a steady e.m.f. is rapidly obtained when the elec- 

 trode vessel is shaken, thus bringing all the solution into contact 

 with the electrode, and he has devised special apparatus for 

 doing this. (20) The Hasselbalch electrode has undergone 

 some modification at the hands of other workers, and of these, 

 that constructed by Clark has found general acceptance. A full 

 description of the electrode will be found in the article by 

 Clark. (16) 



Hydrogen Electrode. 



The Barendrecht electrode consists of a capillary glass tube, 

 having an elongated bulb of about 0.5 c.c. capacity blown upon 

 it. A platinum wire is sealed in through the side of the bulb, 

 and bending at right angles, approaches the construction in the 

 lower part. This is shown in Fig. 7. 



Fig. 7. 



