14 



paper. Withdraw the wire a couple of minutes after the candle 

 goes out. Note the cloudy appearance of the film of water on 

 the wire. The cloudiness was caused by the carbon dioxid 

 formed while the candle was burning. 



Omitting the candle, hang the freshly wetted wire in the 

 empty chimney. Let the film of lime water remain within the 

 chimney for the same length of time as when the candle was 

 used. It does not become cloudy now. The cloudiness in clear 

 lime water is a test or indication that 

 carbon dioxid is present. 



Qhcs. What caused the white scum 

 on the lime water which stood over 

 night ? 



A)is. Some CO^ in the air. 



Ques. How does the CO2 get into 

 the air ? 



Ans. It is formed whenever wood, 

 coal, oil or gas is burned. 



The amount of COjin ordinary air 

 is very small, being only three parts 

 in ten thousand. If the lime water in 

 the loop be left long enough in the air 

 it will become cloudy. The reason it 

 clouds so quickly when the candle is 

 being burned is that a large amount 

 of CO2 is formed. Besides being made 

 by real fiames, CO2 is formed every 

 time we breathe out air. Renew the film of water in the loop 

 and breathe against it gently for two or three minutes. 



The presence of CO2 in the breath may be shown better by 

 pouring oflf some of the clear lime water into a clean glass and 

 blowing into it through a straw. 



An interesting question to end the lesson with is : Why does 

 water put out a fire ? The answer is, not alone because it wets, 

 but because it cools the carbon, which must be hot in order to 

 unite with the oxygen, and prevents the oxygen of the air from 

 getting as near the carbon as before. 



iS. The lesl ■with IJie film of lime water. 



