CARBONIC ACID. 189 



the process is called reduction. Gaseous carbonic ox- 

 ide, has the same effect as carbon, because the affinity 

 of its carbon for oxygen, is only partially satisfied. In 

 the process of reduction, these reducing agents are them- 

 selves converted into carbonic acid, by the oxygen with 

 which they combine. Hydrogen gas, in consequence of 

 its strong affinity for oxygen, is also a powerful reducing 

 agent. The reducing power of carbon may be illus- 

 trated by sprinkling a little litharge on ignited charcoal, 

 and blowing upon it at the same time, to maintain its 

 heat. The litharge, or oxide of lead, will thus be par- 

 tially converted into globules of metal. 



CARBONIC ACID. 

 463. DESCRIPTION. Carbonic acid is a 



What ts car- 



bonic acid? colorless gas, without much taste or smell, 



eS l an( ^ a b ut one an d a na lf times as heavy as 

 air. Other properties are illustrated in the 

 experiments which follow. This gas is found in many 

 mineral waters, and frequently escapes from fissures in 

 the earth. It is a constituent of all limestones and 

 and shells, forms ^^Vo- part of the atmosphere. It is 

 exhaled from the lungs of all animals, and is a product 

 of the combustion of coal and wood. 



464. PREPARATION. Carbonic acid may 



How is carbo- 



nic addpre- be prepared by burning charcoal in oxygen 

 pa1 gas, as directed in paragraph 461. Or it 



may be made by hanging a lighted candle, as long as it 

 will burn, in a bottle filled with ordinary air. In this 



