OXYGEN AND OZONE. 49 



QUESTIONS. 



37. Explain the difference between cohesion and adhesion. What is 

 chemical attraction? Illustrate these forces. 38. What is said about the 

 variety of chemical attractions? What element has the widest range of 

 affinity ? What about the compounds of oxygen with the metals ? Under 

 what circumstances do oxygen and nitrogen combine? 39. What advan- 

 tages result to mankind from the various degrees of affinity? 40. How 

 does solution affect chemical attraction ? Give an example. How does 

 water act on the earth? 41. How does heat modify the attractive force? 

 i2. What is meant by the nascent state ? Why are gases active in this 

 condition ? 43. Name two other circumstances which influence chemical 

 attraction. 44. What are monatomic bodies? Give examples of com- 

 pounds of monatomic elements. What other classes are named? How 

 do these mono-, di-, tri-, and tetr-atomic elements combine ? How is at- 

 omicity expressed in symbols ? What is said of the variableness of this 

 atom-fixing power ? Explain the division into artiads and perissads. What 

 is the atomicity of oxygen ? what of phosphorus ? what of hydrogen ? 



CHAPTER V. 



OXYGEN AND OZONE. 



45. Composition of the Air. The air is composed chiefly 

 of two ingredients, oxygen and nitrogen, which are ele- 

 mentary substances, gaseous in form. These are not united 

 chemically in the air, but are only mingled together. The 

 atmosphere is a mere mixture of gases, just as alcohol and 

 water form a fluid mixture. We will now study oxy- 

 gen at some length, and then take up nitrogen in the next 

 chapter. 



46. Abundance and Importance of Oxygen. Oxygen is 

 the most abundant of all substances. It forms nearly one 

 half the whole bulk of material substances in our earth. 

 It constitutes by weight nearly one fourth of the atmos- 

 phere, eight ninths of the waters of the earth, and about 



C 



