CHAPTER XIII 



Plant Chemistey 



Chemistry, the science which studies what everything is 

 made of, can tell us a good deal that we never could guess 

 by ourselves. For example, the air that we breathe is not 

 one thing, but three or four, and is made chiefly of the gases 

 oxygen and nitrogen. These are called elements, because 

 they cannot be farther divided. Other elements may be com- 

 mon, such as iron, silver, gold, lead ; but not all common 

 materials are elements. Water is made of hydrogen and 

 oxygen ; salt is made of sodium and chlorine ; wood is made 

 of several elements, different woods being different in their 

 make-up. These are all compounds. The chemist, by 

 methods which we do not need to study, can find out the ele- 

 ments of which any compound is made. 



Plants, he tells us, are made chiefly of thirteen elements, 

 some of them in very small amounts. They are combined 

 in various ways. Water is the largest part of any growing 

 plant, arid even when these plants are dried water is often 

 still the largest part. Grass, when it is dried into hay, 

 loses most of its moisture ; but turnips, cabbages, and other 

 such crops, keep their moisture for a long time. Shred some 

 cabbage, or slice a turnip or potato, weigh it, and set it over 

 the fire, or in the sun, until it is quite brittle. Then weigh 

 it again, and see how much water it has lost. If you want 

 to see how much more water can be driven off, put it in an 

 oven which is not so hot as to scorch the plant, and then 

 weigh again. 



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