THE USE OF THE COLORIMETER IN THE INDICATOR 



METHOD OF H ION DETERMINATION 



WITH BIOLOGICAL FLUIDS 



B. M. DUGGAR. 



Physiologist to the Missouri Botanical Garden, im, Charge of Graduate Laboratory 



Professor of Plant Physiology in the Henry Shaw School of Botany of 



Washington University 



and C. W. DODGE 



Formerly Rufus J. Lackland Fellow in the Henry Shaw School of Botany of 



Washington University 



In recent years it has become essential that physiologists, 

 bacteriologists, and biochemists generally shall be able to de- 

 termine accurately and conveniently the approximate actual 

 reaction or hydrogen ion concentration of solutions or media 

 of various types. It is almost inconceivable that any exten- 

 sive work with biological solutions, including fermentation 

 products and culture fluids, may proceed without adequate 

 consideration of this factor. 



It is clearly recognized that as an absolute standard in the 

 measurement of the H ion concentration of solutions one 

 must rely upon the use of the hydrogen electrode, whether 

 with or without the more recent developments in the way of 

 direct-reading potentiometers. Nevertheless, the electrical or 

 gas-chain method requires considerable physico-chemical ex- 

 perience and a type of apparatus not commonly available to 

 the physiologist or bacteriologist. 



To students working in the fields just mentioned and em- 

 ploying nutrient solutions, decoctions, plant juices, the 

 products of fermentation, etc., the indicator method in its 

 present standard of development makes a strong appeal. 

 This is true because: (1) an adequate degree of accuracy is 

 usually attainable by this means, especially if the standard 

 solutions are occasionally checked by the electrometric 

 method; (2) the indicator method has special application 

 where the quantity of material available may be small and 

 the determinations need to be made promptly, as occasions 



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



(61) 



