SCIENCE OF COMMON THINGS. 209 



Carbonic acid a poison. Crowded room unhealthy. 



2. Carbon in. the Hood unites readily -with oxygen 

 during respiration ; and 



3. Carbonic acid is formed in large quantities during 

 the chemical changes which we call fermentation. 



1302 Js carbonic acid in any degree wholesome f 



No / it is fatal to animal life, and (whenever it is 

 inhaled) acts like a narcotic* poison, producing drowsi- 

 ness, which sometimes ends in death. 



1303 When persons commit suicide by building a charcoal fire in a 

 closed room, what occasions their death ? 



The inhalation of carbonic acid, which is generated 

 by the combustion of the charcoal. 



1304 How can any one know if a place be infested with carbonic acid 

 gasf 



If a pit or well contain carbonic acid, a lighted candle 

 (let down into it) will be instantly extinguished. The 

 rule, therefore, is this : where a candle will burn, a man 

 can live / but what will extinguish a candle, will also 

 destroy life. 



1305 Why does a crowded room produce headache? 



Because we breathe air vitiated by the crowd. 



1306 Why is the air of a room vitiated by a crowd ? 



Because it is deprived of its due proportion of oxy- 

 gen, and loaded with carbonic acid. 



1307* How is the air of a room affected thus by a crowd ? 



The elements of the air inhaled are separated in the 

 lungs ; the oxygen, incorporated in the blood, forms 

 carbonic acid ; and the carbonic acid (together with 

 the nitrogen) is thrown back again by the breath into 

 the room, 



1308 Is all the nitrogen rejected by the lungs f 



Yes ; all the nitrogen of the air is always expired. 



1300 How much oxygen does afull-groivn person consume per hourf 



It is calculated that an adult of average size absorbs 



* A narcotic is a substance which, when used as a medicine, relieves 

 pain and produces sleep, but in poisonous doses produces death. Opium, 

 laudanum, tobacco, etc,, are narcotics. 



