48 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



Complete reduction of these sugars is difficult, if not impos- 

 sible, to accomplish by boiling for 60 to 90 minutes. Ordinarily, 

 inversion is complete to the extent of 96-97 per cent. Heating 

 for a longer time will accomplish more inversion, but is offset by 

 an increasing destruction of the resulting monosaccharides. 



A trial of the method developed by Ling and Rendle ('05) 

 showed that this could not be used because of (1) a clouding 

 of the culture solution immediately upon addition of the Feh- 

 ling's, making it practically impossible to observe discharge of 

 blue color upon nearing the end point, and (2) the CuOa does 

 not settle readily. The trouble is probably due largely to the 

 amino acids of the peptone in the Dunham's solution employed 

 (cf. Davis and Daish, '13). 



i;i-:a!) knts and SOLUTIONS 



Fehling's solution. — It was found best to use the Soxhlet-Feh- 

 ling solution, preliminary tests having demonstrated that the 

 solution as modified by Allihn contained too much alkali, when 

 made up with NaOH at the rate of 178 gins, per liter. 



Cuprous oxide solvent. — The ferric sulphate-sulphuric acid- 

 cuprous oxide solvent recommended by Shaffer ('14) was em- 

 ployed. This solvent contains 10 per cent ferric sulphate, Fe 2 - 

 (SO.i) 3 , in 25 per cent sulphuric acid. It is a very active solvent, 

 and care must be taken in watching for the end point. To be 

 efficacious it should be made up by mixing equal parts of a 20 

 per cent aqueous ferric sulphate and 50 per cent sulphuric acid. 

 The ferric sulphate should be dissolved in hot water, filtered 

 while hot, and the warm acid mixed with the warm ferric sul- 

 phate solution. Just enough permanganate should be added to 

 oxidize any ferrous salt which may be present. 



Potassium permanganate solution. — The potassium perman- 

 ganate used was made up according to Olsen ('10). Freshly pre- 

 pared and carefully standardized N/20 permanganate was em- 

 ployed for titration. One cc. of N/20 permanganate is equivalent 

 to 3.18 mgms. of copper. 



TECHNIQUE 



The determination of reducing sugars. — The following tech 

 nique was followed in determining amounts of reducing sugars ii 

 carbohydrate broth cultures of bacteria. Certain slight modi 



