THE PLANT AND THE AIR. 21 



charred plant into a strong iron vessel, having only one small 

 open pipe leading from it, we would find that there were 

 gases coming away that would burn with a flame ; and when 

 you are further advanced in the study of chemistry you will 

 be able to prove that these gases contain, besides carbon, 

 another substance also, called hydrogen. 



In addition to these two, carbon and hydrogen, both of 

 which will burn in the air, there are in the plant small quan- 

 tities of nitrogen and sulphur and some oxygen. All of this 

 cannot be proved by you at present, but you will now have to 

 accept the statement that these parts of the plant that are 

 burned up contain carbon, hydrogen, oxygen, nitrogen, and 

 sometimes sulphur in varying quantities. The chemist, for 

 shortness, refers to them often simply by the first letters, thus : 

 C H O N S. 



WHAT THE PLANT GETS FROM THE AIR. The next 

 question is as to where these elements came from and when 

 they got into the plant. If they came from the soil they must 

 have been contained either in the water or in the salts or 

 mineral matter carried in through the roots. Water is a 

 compound of only two substances, hydrogen and oxygen. 

 Two of them, then, may have come from the rains and soil 

 water. The sulphur and the nitrogen may have come from 

 the soil in part or in whole, for we sometimes find soluble com- 

 pounds of sulphur in the soil, and also compounds of nitrogen. 

 But the carbon which is found in such large quantity does 

 not come from the water, nor from the mineral matter of the 

 soil. There is only one other source, and that is the atmos- 

 phere, or, as we say, the air. If the carbon comes from the air, 

 we at once conclude that it gets into the plant through the leaves. 

 And how wonderfully well supplied is every plant with leaves 

 for taking in food from the air ! 



The air is a mixture of gases. Coal and charcoal are almost 

 pure carbon, so that we think of carbon as being a solid. And 



