NITROGEN. 



THE ATMOSPHERE. 



According to the careful experiments of Dr. Prout, 100 cubic 

 inches of atmospheric air, deprived of aqueous vapour and the 

 small quantity of carbonic acid it usually contains, weigh 

 31.0117 grains, at 60 and 30 Bar. Its density at the same 

 temperature and pressure is estimated at 1000, and is con- 

 veniently assumed as the standard of comparison for the den- 

 sities of gaseous bodies, as water is for solids and liquids. 

 Hence, at 62, air is 815 times lighter than water, and 1 1,065 

 times lighter than mercury. The bulk of air varies with its 

 temperature and the pressure affecting it, according to the same 

 laws as other gases (pages 11 and 66.)"* 



The mean pressure of the atmosphere at the surface of the sea 

 is generally estimated as equal to the weight of a column of 

 mercury of 30 inches in height, which is about 1 5 pounds on 

 the square inch of surface, and is equivalent to a column of 

 water of nearly 34 feet in height. The oxygen alone is equal 

 to a column of 7-8 feet of water over the whole earth's surface, 

 from which an idea may be formed of the immense quantity of 

 that element, and how small the effect must be of the oxidating 

 processes observed at the earth's surface in diminishing it. If 

 the atmosphere were of uniform density its height, as inferred 

 from the barometer, would be 11,065 times 30 inches, or 5.238 

 miles, but the density of air being proportional to the pressure 

 upon it, diminishes with its elevation, the superior strata being 

 always more rare and expanded than the inferior strata upon 

 'which they press. 



* The rate of the expansion of gases by heat has lately been corrected by Rud- 

 berg, who finds that 1 volume of gas at 32 becomes 1.365 vol. at 212, which gives 

 a dilatation of 0*002028, or l-493rd part, instead of l-480th of the bulk at 32, for 

 each degree Fahrenheit. If the expansion be expressed in parts of the bulk at 

 Fahr. which is more convenient for calculation, the expansion is 1-461 part for 

 each degree. The volume of a gas at being 1, at any higher temperature it is 



Temp. Fahr. . 

 always = 1 + f^ 



