5* 



Scientific Proceedings (71). 



33 (1097) 



The availability of certain indicators in the determination of 



gastric acidity. 



By Chester C. Fowler, Olaf Bergeim, and P. B. Hawk. 



[From the Department of Physiological Chemistry, Jefferson 

 Medical College.] 



A comparative study was made of certain indicators which 

 have been used in the titration of gastric juice for free and total 

 acidity and for the colorimetric determination of the H ion con- 

 centration of the same. The findings apply particularly to titra- 

 tions where small amounts of gastric juice are available and many 

 determinations must be carried out. 



Phenolphthalein was the most satisfactory indicator for total 

 acidity in spite of the fact that values obtained with it are slightly 

 high, because the end point is definite and speed and accuracy are 

 attainable with its use while the use of litmus or alizarin requires 

 more time and the end points cannot be determined with accuracy. 



For the titration of free acidity the iodometric method was 

 found most useful. In the higher acidities dimethylaminoazo- 

 benzene may be used with an equal degree of accuracy and may be 

 preferred where much starch is present. Congo red possessed 

 no advantages over the foregoing in the determination of free 

 acid but gives high results and the end point is not sufficiently 

 sharp. 



Colorimetric H ion concentration determinations when applied 

 to gastric contents containing varying quantities of protein and 

 salts have so far proven inaccurate and unavailable for following 

 changes in reaction during digestion. Better results have been 

 obtained after partial removal of protein by short dialysis through 

 collodion sacs according to a procedure similar to that used by 

 Levy, Rowntree, and Marriott 1 for blood. The use of adsorbents 

 for protein and substitutive colloid in standards did not give com- 

 pletely satisfactory comparative results, though attempts are 

 still being made in this direction. 



1 Levy, Rowntree, and Marriott, Arch. Int. Med., 16, 389, 1915. 



