132 'Introduction to the Study of Science 



proportion. It appears that wherever combustion occurs, 

 whether slow or rapid, carbon dioxid is produced. Combustion 

 is going on everywhere in the world, so that the quantity 

 produced must be large. The following data may be suggestive 

 of the amount produced by just one sort of combustion, that 

 of coal. 



Coal on the average contains about eighty per cent carbon, a 

 small percentage of hydrogen, and a small amount of incom- 

 bustible substances that remain as ash. More than a thousand 

 million tons of coal are mined and burned in a year. The 

 burning is often incomplete as evidenced by the quantities of 

 escaping smoke and soot ; but for our present purpose it may 

 be assumed that combustion is complete. 



Carbon, when burned, combines with enough oxygen to pro- 

 duce more than three and one half times its own weight of 

 carbon dioxid; that is to say, one pound of carbon unites 

 in combustion with enough oxygen to produce three and one 

 half pounds of carbon dioxid. How many pounds of oxygen 

 are taken from the air for each pound of carbon burned? 



Now multiply the thousand million tons of coal by eighty per 

 cent, the average amount of carbon, to find the total carbon 

 content ; and multiply this product by three and one half to 

 find the quantity of carbon dioxid produced. The output of 

 carbon dioxid from this one source is seen to be stupendous. 



This is only one of the many ways in which carbon dioxid is 

 produced and liberated in the air. All fuels and all foods con- 

 tain carbon in large proportions, and when consumed are 

 oxidized or turned into large amounts of carbon dioxid. Let us 

 consider a few typical instances from everyday life. 



Exercise : Testing for carbon dioxid. Blow through a glass tube 

 into a beaker containing limewater. What does the reaction indi- 

 cate? If you can get a bellows, fill it with air from near the floor of 

 the room and force it through the limewater. Is the effect similar 

 to that of air expired from the lungs ? 



Heat a small quantity of sugar in a test tube or iron spoon until 



