22 ENVIRONMENT OF LIVING THINGS 



burning match lowered into the jar, the match will at once go out, 

 showing the presence of a gas heavier than air which will not 

 support a flame. We might suspect the presence of nitrogen, but 

 nitrogen would not respond to the test which follows. If we pour 

 into the jar a few spoonfuls of limewater, 1 a colorless liquid, and 

 shake it up with the gas in the jar, the limewater turns milky in 

 color. This is a test for a compound known as carbon dioxide. 

 This compound was evidently formed by the union of the 

 carbon with the oxygen of the air in the jar. 



All organic or living substances, when oxidized, form 

 carbon dioxide. That oxidation of carbon takes place 

 within our own bodies may easily 

 be proved by exhaling through a 

 clean glass tube into some lime- 

 water. The heat of our body 



(98.5 F.) is the result of oxidation Oxyger > in - the air 



taking place within the body, fr j j^ =\> 



The heat given off from oxidation . , 



Diagram of combustion or rapid 

 Of WOOd Or COal in a Stove IS de- oxidation in a stove. 



termined by the supply of oxygen 



we allow to pass to the burning material. If we open the 

 draft, allowing more oxygen to get to the fire, we increase 

 the heat by more rapid oxidation; if we shut off the oxygen 

 supply, we decrease the amount of oxidation. Does this help to 

 explain our deep breathing after doing hard physical exercise? 



Problem II. Are mineral matter and water present in liv- 

 ing things ? (Laboratory Manual, Prob. //.) 

 (a) Mineral matter. 

 (6) Water. 



Mineral Matter in Living Things. If a piece of wood is burned in a 

 very hot fire, the carbon in it will all be consumed, and eventually nothing 

 will be left except a grayish ash. This ash is well seen after a wood fire in 

 the fireplace, or after a bonfire of dry leaves. It consists entirely of min- 

 eral matter which the plant has taken up from the soil dissolved in water, 

 and which has been stored in the wood or leaves. 



1 Limewater can be made by shaking up a piece of quicklime the size of your 

 fist in about two quarts of water. Filter or strain the limewater into bottles, and it 

 is ready for use. 



