CARBONIC ACID. 265 



instantly extinguished. The rule, there- 

 fore, is this Where a candle will burn t 

 a man can live ; but what will extinguish 

 a candle, will also destroy life. 



Q. Why does a MINER lower a CANDLE into 

 a mine, before he descends ? 



A. Because the candle will be extin- 

 guished, if the mine contains carbonic 

 acid gas : but if the candle is not extin- 

 guished, the mine is safe, and the man 

 may fearlessly descend. 



Q. Wliy are PERSONS sometimes KILLED, by 

 leaning over BEER VATS ? 



A. Vats (where beer has been made) 

 contain a large quantity of carbonic acid 

 gas, produced by the "vinous ferment- 

 ation" of the beer ; and when a man 

 incautiously leans over a beer vat, and 

 inhales the carbonic acid, he is imme- 

 diately killed thereby. 



Q. Why are PERSONS often KILLED, who 

 enter BEER VATS to clean them f 



A. Carbonic acid (being heavier than 

 atmospheric air) often rests upon the 

 bottom of a vat : when, therefore, a person 

 enters the vat, and stoops to clean the 



Aa 



