1919] 



DUGGAR — MICRO-COLORIMETER IN H ION DETERMINATION 181 



is one slight optical defect due to the fact that the surfaces of 

 the liquids in the plunger tubes are not plane surfaces, but this is 

 of no practical consequence in the actual determination, es- 

 pecially where a strong and standard source of light is employed. 

 It is recommended that any of the so-called daylight bulbs be 

 employed in this work. Using the method mentioned no dif- 

 ficulty whatever has been experienced in determining rapidly and 

 effectively the hydrogen ion concentration of such dark liquids 

 as oxidized potato juice, carrot decoction, and decoctions of 

 plants containing considerable chlorophyll. 



It is perhaps unnecessary to add that the technique suggested 

 is equally applicable where the large types of colorimeters are 

 employed, such as the Dubosq of standard size, or the Kober 

 (if plunger tubes are detachable), but somewhat larger quantities 

 of solutions will be required. 



Graduate Laboratory, Missouri Botanical Garden. 



