PlCRAMATES AS A MEASURE OF REDUCTION 



77 



37 (1997) 



Some limiting factors in the use of picramate as a measure of 



reduction. 



By SISTER MARY DENISE, S. S. N. D., and A. R. ROSE. 



[From the Department of Chemistry, Fordham University, 



New York City.] 



This report pertains to the colored solutions formed by the 

 reduction of picric acid. The color is not due to a single sub- 

 stance but to a mixture of several colored substances. In solu- 

 tions where the color is due to some one substance, there is a 

 simple and definite ratio between the concentrations and the 

 color values. When the color is clue to two or more substances 

 a definite ratio holds for differences in concentrations only 

 within relatively narrow limits. The colorimetric determina- 

 tion of picrate reduction mixtures is therefore limited. It is 

 thought that this limitation can in part be counteracted by iso- 

 lating the most characteristic component of the color. This is 

 done by extracting the products after the reduction of picrates 

 with immiscible organic solvents, shaking this extract with an al- 

 kaline solution. The alkaline solution assumes a color which is 

 qualitatively very like the original reduction mixture. The number 

 of colored constituents has been reduced. TJie color values of the 

 reduction mixture and the isolated color component are affected 

 by change in temperature. One degree centigrade decreases the 

 color value one per cent. Salts, cane sugar and alkalies increase 

 the color value. These tests were made by diluting picramate 

 mixtures with molar solutions and comparing them, with a 

 standard prepared in the same manner as the picramate mix- 

 tures which were tested. In half -molar solutions there is but a 

 slight error for sodium chlorid; for the sugar it came to 10 

 per cent., and for potassium carbonate to 12 per cent. Molar 

 solutions gave an error of 17 per cent, in the case of salt, 14.5 

 per cent, for sugar, and 16 per cent, for potassium carbonate. 

 Sodium hydroxide at this concentration caused an error of 8 

 per cent. Higher concentrations made very difficult readings. 

 Sodium chlorid in three-molar concentrations decreased the 

 readings 25 per cent, and five-molar 29 per cent. Sodium hy- 

 droxide in two-molar solution caused a 25 per cent, decrease 



