CHEMISTRY 47 



kingdoms of nature, of any substance: it enters largely into 

 the composition of living animal bodies, and constitutes, ac- 

 cording to Johnston, half the weight of all green or newly 

 gathered vegetables which are cultivated for the use of man. 



Without water, neither animals nor plants could exist, (with 

 their present organization,) the earth would become a scorched 

 and sterile waste : many compounds resulting from chemical 

 affinities which require the presence of water, would be un- 

 known : the varieties of climate which now exist would also 

 to a great extent be unknown. Water in its relations to vege- 

 table life, and also its meteorological influences, will be more 

 particularly discussed in a subsequent part of this book. 



THE ATMOSPHERE ITS PROPERTIES AXD RELATIONS. 



The atmosphere which we breathe is an immense ocean of 

 gaseous fluid : the depth of this ocean is about 45 miles, at 

 the bottom of which we live, or rather, it extends about 45 

 miles above the surface of the earth, which it entirely sur- 

 rounds. It is composed of the two gases oxygen and nitro- 

 gen, in volume in the proportions of about 21 of the former 

 to T9 of the latter in 100. It contains also, according to 

 Sausseur, ^ jV ^ f ^s bulk of carbonic acid. 



The quantity of this gas is greater in cities than in the coun- 

 try, slightly less in the air over the seas and great lakes, it 

 is less over a wet than a diy soil, and by day than by night. 

 The air is imbued with watery vapor which varies in different 

 climates : it holds in suspension, traces of various animal and 

 vegetable matters and ammonia. Heat and electricity also 

 exist more or less at all times in the atmosphere. Air diffuses 

 itself everywhere, penetrates the minutest recesses of every 

 porous body, and presses with the almost incredible weight of 

 15 pounds to every square inch of the earth's surface: it is 

 transparent, colorless, invisible, elastic, tasteless and inodorous. 

 The two essential elements of the atmosphere, viz. oxygen and 



