SCIENCE OF COMMON THINGS. 207 



Carbonic acM gas. The composition of the air never varies. 



functions of life would be called into such rapid action 

 as to soon exhaust the powers of the system. 



1370 Are the two gases, oxygen and nitrogen, existing in tlie atmo- 

 sphere, chemically combined, or merely intermingled ? 



They are merely mixed, and not combined with each 

 other. 



1377' Does thv atmosphere always contain any other ingredients besides 

 oxygen and nitrogen f 



There is always in the air, at all places, carbonic acid 

 gas, in variable proportions, and watery vapor, besides 

 the odoriferous matter of flowers and other volatile 

 substances. 



1378 What is carbonic acid gas f 



A gas formed by the union of carbon and oxygen ; 

 it used to be called fixed air. Its chemical com- 

 position is one atom of carbon united to two of 

 oxygen. 



1379 Is the air collected on the tops of high mountains, over marshes 

 in hospitals, and over deserts, the same in character and composition f 



It is not found to vary, but is the same in all regions 

 of the earth and at all altitudes. 



1380 Are the component parts of air, oxygen, nitrogen, carbonic acid, 

 and watery vapors, of different specific gravities, or do they all differ in 

 weight ? 



They are all different, carbonic acid gas being the 

 heaviest. 



1381 Then, as we have before stated that they are merely mixed, and 

 not combined, why do they not arrange themselves in the order of their densi- 

 ties, and float one upon the other, as oil and water do when mingled f 



Because of a wonderful principle or law of nature, 

 that when two gases of different weights or specific 

 gravities are mixed together, they cannot remain sepa- 

 rate, as fluids of different densities do, but diffuse them- 

 selves uniformly throughout the whole space which 

 both occupy. 



1383 Carbonic acid is tiventy times heavier than hydrogen gas ; if we 

 fill the lower part of a tatt jar with carbonic acid, and the upper part with 

 kydrogen, will the two gases mix ? 



After a few hours the two gases will be found equally 



