30 THE EEASON WHY. 



1 A prudent man forseeth the evil, and hideth himself ; but the simple pass on, 

 and are punished." PROVERBS xxvii. 



six times successively, it would have parted with all its oxygen, and 

 could no longer sustain life. 



14. Is the impure air sent out of the lungs lighter or 

 heavier tlian common air ? 



At first, being rarefied by warmth, it is lighter. But, if undis- 

 turbed, it would become heavier as it cooled, and would descend. 



15. Why is it proper to have beds raised about two feet 

 from the ground ? 



Because at night, the bed-room being closed, the breath of the 

 sleeper impregnates the air of the room with carbonic acid gas, 

 ffhich, descending, lies in its greatest density near to the floor. 



16. What are the chief sources of carbonic acid gas ? 



The vegetable kingdom (as will be hereafter explained), the com- 

 bustion of substances composed chiefly of carbon, the breathing of 

 animals, and the decomposition of carbonic compounds. 



17. Is Ijreatliing a kind of combustion ? 



It is. In the breathing of animals, the burning of coal?, or of 

 wood, or candles, &c., similar changes occur. The oxygen of the 

 air combines with the carbon of the substance said to be burnt, 

 and forms carbonic acid gas, which unfits the air for the pur- 

 poses of either breathing or of burning, until it has been renewed by 

 admixture with the air. 



18. What is carbon ? 



It is one of the elementary bodies, and is very abundant through- 

 out nature. It abounds mostly in vegetable substances, but is also 

 contained in animal bodies, and in minerals. The form in which 

 it is most familiar to us is that of charcoal, which is carbon almost 

 pure. 



19. What is meant by an elementary body ? 



An elementary body is one of those substances in which chemistry 

 is unable to discover more than one constituent. For instance, the 

 chemist finds that water is composed of oxygen and hydrogen. 

 Water is therefore a compound body. But carbon consists of carbon 

 only, and therefore it is called a simple, or elementary body. 



