PASSAGE OF OXYGEN THROUGH THE BODY 113 



Exercises. i. Describe the properties of oxygen. How does it 

 unite with other elements? How does it support combustion? 



2. State the purpose of oxygen in the body. What properties 

 enable it to fulfill this purpose? 



3. What is the proof that oxygen does not remain permanently in 

 the body? How does the oxygen entering the body differ from the 

 same oxygen as it leaves the body? 



4. What is the necessity for the continuous introduction of oxygen 

 into the body, while food is introduced only at intervals ? 



5. How are the red corpuscles able to take up and give off oxygen? 

 How is the plasma able to take up and give off carbon dioxide? 



6. If thirty cubic inches of air pass from the lungs at each expiration 

 and 4.5 per cent of this is carbon dioxide, calculate the number of cubic 

 feet of the gas expelled in twenty-four hours, estimating the number of 

 respirations at eighteen per minute. 



7. What is the weight of this volume of carbon dioxide, if one cubic 

 foot weigh 1.79 ounces? 



8. What portion of this weight is oxygen and what carbon, the ratio 

 by weight of carbon to oxygen in carbon dioxide being twelve to thirty- 

 two? 



9. What is the final disposition of carbon dioxide in the atmos- 

 phere? 



PRACTICAL WORK 



To show the Difference between Free Oxygen and Oxygen in Com- 

 bination. Examine some crystals of potassium chlorate .(KC1O 3 ). 

 They contain oxygen in combination with potassium and chlorine. 

 Place a few of these in a small test tube and heat strongly in a gas or 

 alcohol flame. The crystals first melt, and the liquid which they form 

 soon appears to boil. If a splinter, having a spark on the end, is now 

 inserted in the tube, it is kindled into a flame. This shows the presence 

 of free oxygen, the heat having caused the potassium chlorate to decom- 

 pose. The difference between free and combined oxygen may also be 

 shown by decomposing other compounds of oxygen, such as water and 

 mercuric oxide. 



Preparation and Properties of Oxygen. Intimately mix 3 grams 

 (\ teaspoonful) of potassium chlorate with half its bulk of manganese 

 dioxide, and place the mixture in a large test tube. Close the test 

 tube with a tight-fitting stopper which bears a glass tube of sufficient 



