THE MICRO-COLORIMETER IN THE INDICATOR 

 METHOD OF HYDROGEN ION DETERMINATION 



B. M. DUGGAR 



Graduate 



Shaw 



Washingt 



In a recent 



drawn to the use of the 



colorimeter in determining accurately by the indicator method 

 the hydrogen ion concentration of pigmented biological fluids. 

 In the method there discussed there was employed the well- 

 known principle of compensating for the color of the test solution 

 by introducing the test solution also as a shield solution. It was 

 pointed out that in order to avoid the optical difficulties of the 



tintometers or com 

 les of the colorimet 



all the ad- 

 within an- 



micro 



other are arranged as cup and shield respectively. Properly 

 made these cells are expensive, and the method requires about 

 15-20 cc. of the liquid for convenient determinations by the 

 colorimeter. 



Recently I have had occasion to test the hydrogen ion con- 

 centration of some fluids obtainable only in small quantity, and 

 while examining the possibilities of adapting the 

 meter for this work it became clear that the Dubosq type of this 

 instrument lends itself admirably to the colorimetric method in 

 general, and to small quantities of fluid in particular. More- 

 over, as the method is now modified the necessity for special 

 cells is eliminated. Instead of employing two special cells in 

 connection with each plunger of the colorimeter the principle of 

 the new procedure lies in the use of the plunger tube and of a 

 colorimeter cup as cells on each side of the system. When the 

 quantity of test material available is not limited it is customary 

 in our work to employ 5-cc. quantities, and 5-cc. quantities of 

 the standards, the solutions being prepared in small serological 

 test-tubes to each of which is added 3 drops of indicator. With 



1 Duggar, B. M., and Dodge, C. W. The use of the colorimeter in the indicator 

 method of H ion determination with biological fluids. Ann. Mo. Bot. Gard. 6 : 61-70. 

 /. /. 1919. 



Ann. Mo. Bot. Gard., Vol. 6, 1919 



(179) 



