1919] 



DUGGAR AND DODGE — COLORIMETER IN H ION DETERMINATION 69 



instance there is still exhibited a remarkable P H . range, de- 

 termined by Haas for the juices of certain higher plants to 

 be between P H 3.0 and P H 7 or 8. This, moreover, is more or 

 less comparable to the relation of certain mould fungi (nota- 

 bly Penicillium italicum and Aspergillus niger) to the reac- 

 tion of nutrient media. 



From the work here reported on the use of the colorimeter 

 it may be concluded that (1) the difficulties involved in the 

 approximate determination of the hydrogen ion concentra- 

 tion of solutions exhibiting color may be largely overcome; 

 and (2) the useful range of certain brilliant indicators may 

 be so considerably extended that the number of indicators 

 employed may be materially reduced. 



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