208 SCIENCE OF COMMON THINGS. 



Carbonic acid gas in the atmosphere. 



mingled, as much carbonic acid being at the top of the 

 jar as at the bottom. 



13 S3 Does this law appear to be opposed to the principles of the law of 

 gravitation ? 



It appears to be opposed to it ; the only exception we 

 are acquainted with in the natural world. 



1384 How much carbonic acid is estimated to exist in the atmosphere f 



I About one part in two thousand, by volume. 



1335 If this were all collected in one layer over the surface of the earth, 

 how great a thickness would this layer or stratum have ? 



About thirteen feet. 



138Q Can we breathe carbonic acid? 



No the animal immersed in it dies instantly. 



1387* If, then, this singular law of the diffusion of gases did not prevail, 

 would the surface of the earth be habitable ? 



It would not; carbonic gas would fill up all the 

 valleys and lower levels, separating every hill and ele- 

 vation by an invisible ocean of poisonous gas, as im- 

 passable as the barrier between the dead and the 

 living. 



1388 Is it owing to this law that we are enabled to enjoy and perceive 

 at a distance the odor of a flower-garden, or the perfume which has been 

 opened in an apartment f 



It is by this law that a vapor, arising by its own 

 elasticity from a volatile substance, is caused to extend 

 its influence and mingle with the surrounding atmo- 

 sphere, until its effects become so enfeebled by dilution 

 as to be imperceptible to the senses. 



138Q If the oxygen and nitrogen of which our atmosphere is composed 

 were combined together, instead of being merely mingled, what would the 

 compound be ? 



A most deadly poison. 



1390 What gas is generated by a lighted candle or lamp ? 



Carbonic acid gas formed by the union of the carbon 

 of the oil or tallow with the oxygen of the air. 



1391 Under what circumstances does carbon most readily unite with 

 oxygen ? 



1. When its temperature is raised : thus, if carbon 

 be red hot, oxygen will most readily unite with it ; 



