DEMONSTRATION EXPERIMENT SHOWING THE EFFECT OF THE GASES, OXYGEN, CARBON DIOXIDE, AND CARBON MONOXIDE ON BLOOD EDWARD ZETTERBERG, CENTRAL HIGHSCHOOL, MUNCE,INDIANA
This experiment is intended to accompany a study of carbon monoxide. About one pint of blood taken from a freshly killed animal (any animal will do; the author has used blood from sheep, hogs, and cows) should be beaten or stirred rapidly for about five minutes. This prevents complete clotting. Clots will form but there will remain plenty of goodliquid blood for the experiment. Three groups of two pupils each have previously been selected to prepare the three gases needed. Each group should have all apparatus and materials ready for the preparation of the gas assigned to it. In about 10 minutes four wide-mouthed bottles (of about 200 ml. capacity) of each gas are prepared. The completely filled bottles of gas are covered with glass plates and set upright on the table. All superfluous apparatus is then removed from the table. A test-tube rack containing six large test tubes numbered from 1to 6 is set facing the class. The following numbered sections indicate treatment of samples of hlood before pouring 10 ml. in the corresponding test tube. In each case after adding the blood to a bottle of gas a tight-fitting rubber stopper is inserted and the contents are shaken vigorously for about a minute. I. 10 ml. of the original hlood is poured in the first test tube for comparison. 11. 20 ml. of blood are added to a bottle of oxygen. 111. 20 ml. of hlood are added to a bottle of Cop. After shaking, half of the blood is put in the third test tube. IV. The remaining 10 ml. from I11 is added to a bottle of oxygen. V. 20 ml. of blood are added to a bottle of CO. After shaking, half of the blood is put in the fifth test tube. VI. The remaining 10 ml. from V is added to a bottle of COz. Results Test tube 1will show rather dark red blood. Test tube 2 will show bright red blood. Test tube 3 will show darker red than 1. Test tube 4 will show bright red blood. Test tube 5 will show bright red blood. Test tube 6 will show bright red blood. Interpretation of Results 1. Hemoglobin, the red coloring matter of the red corpuscles, combines readily with the gases-oxygen, carbon dioxide, and carbon monoxide. 2. The equation, carbon dioxide-hemoglobin c--, oxyhemoglobin, is 2427
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JOURNAL OF CHEMICAL EDUCATION
DECEMBER. 1931
shown to be a reversible reaction. (The darkening of blood shaken may be repeated with COz and then the brightening by shaking with 0% several times with the same sample of blood.) 3. Hemoglobin combines with CO and forms a very stable compound not darkened by COz. (Oz would likewise have no effect on carbon monoxide-hemoglobin but since the reaction, if any, would not change the color of the bright red carbon monoxide-hemoglobin, the test has been omitted from this experiment.) Value to Pupils 1. 2.
3. 4. 5. 6.
Illustrates the respiratory process in animals of the elimination of C02 and the taking on of 0%. Illustrates reversibility due to mass action d e c t of the gases Oz and
coz.
The importance of chemical change to life is shown. Gives a few pupils a chance to do demonstration work before the class. Reviews preparation of O2and of Cop. Demonstrates preparation of CO. One bottle of this gas should be used to show its combustibility. Discussion to Follow the Experiment
1. Arterial blood compared with venous blood as to color, and oxygen and carbon dioxide content. 2. Carbon monoxide as a cumulative poison. 3. Sources of carbon monoxide poisoning. 4. Uses of CO and industrial methods of preparation. Notes The author tried bubbling the gases through blood but got poor results due to: (1) generators worked erratically; (2) not as rapid mixing of gases and blood as in the shaken bottles; (3) blood with bubbling gases forms a froth which carries much of the blood out of the reaction vessel; (4) takes more time and distributes the attention of the pupils over too many things a t once. The presence of iron in the hemoglobin may be shown by evaporation and ignition of a sample of blood. The residue is leached with nitric acid and this solution added to a solution of potassium thiocyanate or potassium ferrocyanide. (Iron may also be shown to be present in chlorophyll by dissolving the green coloring matter in leaves with wood alcohol, evaporation, and then treating as above.) More bottles of the three gases used are prepared than this experiment indicates are used since i t is desirous sometimes to repeat a test and it is best to have an extra bottle or so handy.
