[Vol. 10 



236 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



HYDROGEN-ION CONCENTRATION 



The P H of the solutions used was determined colorimetrically, 

 using the Clark ('20) series of buffers and indicators. 



REDUCING SUGARS 



Dextrose was used throughout this work, and quantitative 

 determinations were made by the Shaffer and Hartmann ('21) 

 method, using the adaptation of Fehling's solution. 



OXALIC ACID 



For either the qualitative or quantitative determination of 

 oxalic acid the precipitation with calcium acetate in a hot solution 

 acidified with CH.COOH as described by Leffmann ('17) was 

 made use of. The precipitate from the acidified solution was 

 dissolved in H 2 SO< and tested qualitatively with KMnO< and 

 Mn0 2 or determined quantitatively by titration with standard- 

 ized KMn0 4 . 



THE DETERMINATION OF TOTAL CARBON 



It was found desirable to have a means for determining with 

 rapidity the total carbon in the culture solutions used. This 

 involved the oxidation of dextrose, citric acid (peptone in a few 

 instances), and any metabolic derivatives of these substances. 

 A number of dry combustion methods were examined, but besides 

 being complicated and slow required too much equipment. A 

 wet combustion method as sometimes used for carbon determi- 

 nations in soil and steel seemed more feasible, while the method of 

 Friedeman ('21) seemed to fill the need very satisfactorily. 

 Since Friedeman 's work has not been published, a brief account 

 of the method will be included, together with data as to its appli- 

 cation and accuracy in physiological work. 1 



Chemistry of the method. — Oxidation by chromic and sulphuric 

 acids in the presence of HJPO* is made use of in this method. 

 The CO, formed when the reaction mixture is heated is aerated 

 over into a modified Truog ('15) absorption tower and absorbed 



1 The writer is especially indebted to Mr. Friedeman for personal aid in the working 

 up of the method and apparatus used, and for advice on the chemistry involved in 

 its utilization in this line of work. 



