JOURNAL OF CHEMICAL EDUCATION
DEMONSTRATION OF OXIDATION-REDUCTION SYSTEMS CYRIL E. ABBOTT Westminster College, Salt Lake City, Utah
METHYLENE BLUE is excellent for demonstrating oxidation-reduction in witro. A suggested stock solution contains 0.5 mg. of the dye and 1.0 g. of NaOH in 500 ml. of water. When 5.0 ml. of M/10 sugar (glucose or fructose) is added to 10.0 ml. of the dye solntion and the mixture heated to 40°C. it soon becomes colorless. It remains in that condition indefinitely if not agitated, but when shaken with air the color is restored, only to fade out again when the material is allowed to stand. This oxidatiou-reduction cycle may be repeated many times. The speed of reduction is dependent upon temperature, concentration, and kind of sugar. The speed of oxidation of equimolar solutions of fructose, glucose, andgalactose is directlypro~ortional to their nutrient values to certain organisms,' (i. e., fructose > glucose > galactose). Hemoglobin may be substituted for methylene blue. shaken with About 1.0 g. of powdered 500 ml. of water makes suitable material after filtering, provided it is used the day it is prepared. It has the advantage of demonstrating that blood pigment is part of an oxidation-rednction system, but the disadvantage is that the color change is somewhat difficultto follow, since the oxidized material is amber, the reduced red. 1 ABBOTT,C.E.,Proe. Arkansas A d . Sci., 2,45-47 (1947).
Washed red blood cells in physiological saline, mixed with an equal quantity of liquid containing living yeast cells, soon lose oxygen to the latter, becoming deep p ~ r p l e . ~The reaction is reversible, the suspension regaining its red color when shaken with air. In an actual test case, reduction occurred within 30 seconds. Saturation with NaHCOa prevented reduction. experiments with molds indicated that acts as a respiratoryinhibisodium monofluoracetate tor,~ action on washed blood cells confirms this ~in view~of the effect ~ of N~~ H C O~ ~ conclusion, H the and the fact that monofluoracetate dissociated to give an alkaline condition, it is necessary first to buffer the suspension to p ~ 7.0, , under such mg,/ml, of suspension conditions it was found that prevents reduction to the purple stage indefinitely; tirne to 45 1.48 mg./ml. prolongs 0.77 mg./ml, has no inibiting effect,the occurring in 30 seconds, Intelligent discussion of these demonstrations at the time they are performed will help students understand them. DIVLBKIN, D. L., Science, 101,446--451 (1945). ABBOFT, C. E., Sezence, 102, 71 (19451.