92 CHEMISTRY. 



effects does it produce ? 9G. What is said of its absorbing power ? 97. 

 How is this power to be explained? 98. What is the difference between 

 anthracite and bituminous coal ? What is coke ? 99. What is said of 

 black-lead? 100. What of the diamond? 101. What is meant by allo- 

 tropism ? Whence is the word derived ? 102. State various cases in which 

 carbonic anhydride forms ? 103. Describe and explain the common mode 

 of obtaining it? Write the equation given. 104. What are the properties 

 of carbonic anhydride? How is it collected? Show it has weight. 105. 

 What is said of converting gases into solids ? 106. What effect does car- 

 bonic anhydride have on combustion? Illustrate this. 107. What effect 

 on respiration ? How does it differ from nitrogen in this respect ? 108. 

 How does carbonic anhydride act on the stomach? 109. What is "soda- 

 water?" 110. Why is there no true carbonic acid? 111. State what is 

 said of an apparent inconsistency. 112. What is the composition and nat- 

 ure of carbonic oxide? Where do we often see it burning? Explain its 

 production and burning in this case. 113. How may it be prepared ? Why 

 will it burn when forced out of a jar by pouring in water ? Is it poisonous ? 



CHAPTER VIII. 



THE CHEMISTRY OP THE ATMOSPHERE. 



115. Ingredients of the Atmosphere. The air is a mixture 

 of three gases oxygen, nitrogen, and carbonic anhydride. 

 The proportions of these ingredients are changed by cir- 

 cumstances, as you will soon see, and yet wherever the air 

 is free the proportions are always the same. About one 

 fifth of the air is oxygen, and 

 the remaining four fifths nitrogen. 

 The amount of carbonic acid is 

 very small, there being only 4 vol- 

 umes in every 10,000 volumes of 

 air. These proportions are repre- 



sented to the eye in Fig. 27, the 



largest square representing the nitrogen, the one at its side 

 the oxygen, and the smallest the carbonic anhydride. 



