OXYGEN HYDROGEN NITROGEN. 35 



perhaps the most important, offices in the che- 

 mistry, of nature. It is therefore by far the 

 most abundant of the elementary bodies. It 

 is the largest constituent by weight of the 

 ocean, forming eight-ninths by weight of pure 

 water. It forms a fifth part, by bulk, of the 

 atmosphere : and it enters into a large number 

 of combinations with the solid ingredients of 

 the globe. It is possessed of the most exten- 

 sive range of chemical affinities; that is, it is 

 capable of entering into chemical union with 

 by far the greatest number of the other ele- 

 mentary or simple substances. Its connexion 

 with, and its relation to, the vital functions of 

 the animal frame, the necessities of mankind, 

 the purity of the atmosphere, and the renovation 

 of the face of the earth, will come into considera- 

 tion in different portions of this work. When it- 

 combines with another body, the chemical name 

 of that process of union is " oxidation," and 

 when it is completed the resulting substance is 

 an " oxide." 



Hydrogen is also an important element. It 

 forms about one-ninth of the weight of water, 

 which is, in fact, an oxide of hydrogen; it also 

 enters largely into the composition of animal and 

 vegetable structures. 



Nitrogen forms one of the chief constituents 

 of the atmosphere. It is remarkable chiefly for 



