1434
JOURNAL oa CUEMIW EDUCATION
DECEMBER. 1926
AN EXPERIMENT SUITABLE FOR THE DEMONSTRATION OF THE PREPARATION AND PROPERTIES OF OXYGEN AND OF ENZYME ACTION (CATALASE) H. L. W I K O AND ~ J. B. BROWN, COLLEOE OP MEDICINE, Orno STATE UNNERSITY. COLUMBUS, OHIO The usual laboratory method for the preparation of oxygen consists in the decomposition of potassium chlorate by heat, under the catalytic influence of manganese dioxide. This procedure necessitates the devising and setting up of apparatus and involves certain precautions. As a rule the beginner devotes more time to these considerations than to the study of the properties and reactions of oxygen. Another important method for preparing this gas is by electrolysis of water. The apparatus in this instance is too expensive to be used other than for a lecture demonstration. I t occurred to us that a more simple method for the laboratory preparation of oxygen might be based on the catalytic decomposition of hydrogen peroxide. This may be brought about very readily by one of the class of biological catalysts or enzymes called catalase. This substance, which is found in most tissues, occurs to an especially great extent in ordinary compressed bakers' yeast. Thus, for example, when yeast is added to HzOz a vigorous evolution of oxygen takes place. The gas thus obtained can be readily used for any experiments in the study of its properties. The chemical reaction which is involved is as follows: 2HO = 2H2O OZ
+
Theoretically from one volume of three per cent hydrogen peroxide ten volumes of oxygen should result, but practically the yield is less. Directions for the Experiment Mix a cake of compressed yeast* in a beaker with 200 cc. of water and stir until a uniform suspension results. Add to this mixture 200 cc. of 3 per cent hydrogen peroxide in a 500-cc. flask. After mixing, the flask is filled level full with water, a watch glass placed over the top and the whole quickly inverted over water. A vigorous evolution of oxygen immediately occurs which expels the reaction mixture from the flask. In five to ten minutes the flask is nearly full of oxygen. I t can be covered with the watch glass and removed from the water. The gas is now ready for any further experiments desired. I t is to he observed that a considerable excess of peroxide is used, for the sake of simplicity of apparatus, since the reaction mixture is being expelled from the flask as the reaction proceeds. Should the instructor *We are indebted to the Fleischmann Company for supplies of yeast for use in these experiments.
so desire, he may advise the use of other more complex apparatus so that all of the oxygen liberated may be collected. With slight variations in the apparatus including the use of a gas burette, the experiment may he adapted to a quantitative study of the rate of liberation of oxygen.
