126 CHEMISTRY OF RESPIRATION. 



EXPERIMENT 13. Scrape a piece of magnesium ribbon 

 bright, and place it in a glass of water. In a day or so it will 

 be found to be coated with a white substance, which is mag- 

 nesium oxid, the same as was produced by the rapid oxida- 

 tion, or combustion. In the latter experiment we should 

 probably call it magnesium rust. 



EXPERIMENT 14. Exhale slowly through a tube extend- 

 ing to the bottom of a fruit-jar. Continue exhaling for a long 

 time, to be sure to drive out the air that was in the jar. Cap 

 the jar tightly, and set it in a warm place for twenty-four 

 hours. It will have a bad odor from the putrefaction of the 

 organic matter thrown out in the wastes from the tissues. 



EXPERIMENT 15. With a pair of bellows force the air of 

 the room through a small quantity of lime-water. By con- 

 tinuing the process for a long time it may be shown that there 

 is carbon dioxid in the air, but not nearly so much as in the 

 expired breath. 



EXPERIMENT 16. Exhale for a long time through a small 

 quantity of sulphuric acid (chemically pure), using a pipette 

 with a large bulb, so that the acid could not be drawn up into 

 the mouth (the acid is very strong). The acid will gradually 

 grow dark colored, indicating the presence of organic matter. 



EXPERIMENT 17. Hold a thermometer at arm's length. 

 It indicates the temperature of the air of the air that you 

 are breathing in. Breathe for a few minutes upon the bulb of 

 the thermometer, and the fact is clearly shown that the air 

 we breathe out is much warmer than the air that we breathe 

 in. 



These experiments show that breathed air has gained : 



1. Heat. 



2. Water vapor. 



3. Carbon dioxid. 



4. Waste products, or impurities, having no definite name, 



