COMMON THINGS. 



AIR 



1. Air most necessary to existence. 2. Respiration. 3. Fresh air neces- 

 sary. 4. Air is material. 5. Its weight and momentum. 6. How 

 weighed. 7. The atmosphere. 8. Its pressure. 9. Why bodies not 

 crushed by it. 10. Illustrated by a cupping-glass. 11. Compres- 

 sibility. 12. Elasticity. 13. Elastic pressure. 14. Varies with the 

 density. 15. Strata of atmosphere near the surface of the earth 

 and at greater elevations. Diminished pressure at great elevations. 

 16. Anciently supposed to be an element. 17. Air a compound. 

 18. Gases. 19. Proportion of the constituents of air. 20. Azote or 

 nitrogen. 21. Oxygen gas. 22. Combustion. 23. Its products. 

 24. Carbonic acid. 25. Unfit for respiration. 26. Impure air pro- 

 duced in warming and lighting. 27. Ventilation of public buildings. 



LABDKER'S MUSEUM OF SCIEXCE. B 1 



No. 14. 



