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CHAPTER III 



OXYGEN AXD THE CHIEF ASPECTS OF ITS SALINE COMBINATIONS. 



ON the earth's surface there is no other element which is so widely dis- 

 tributed as oxygen in its various compounds. 1 It makes up eight-ninths 

 of the weight of water, which occupies the greater part of the earth's 

 surface. Nearly all earthy substances and rocks consist of compounds 

 of oxygen with metals and other elements. Thus, the greater part of 

 sand is formed of silica, SiO 2 , which is a compound of oxygen with silicon, 

 and contains 53 p.c of oxygen ; clay contains water, alumina (formed of 

 aluminium and oxygen), and silica. It may be considered that earthy 

 substances and rocks contain up to one-third of their weight of oxygen ; 

 animal and vegetable substances are also very rich in oxygen. With- 

 out counting the water present in them, plants contain up to 40, and 

 animals up to 20 p.c. by weight of oxygen. Thus, oxygen compounds 

 predominate on the earth's surface, and form about one-half of the 

 whole of the solid and liquid matters of the earth's crust. Besides 

 this, a portion yet remains free, and is contained in admixture with 

 nitrogen in the atmosphere, forming about one-fourth of its mass, or 

 one-fifth of its volume. 



Being so widely distributed in nature, oxygen plays a very im- 

 portant part in it, for a number of the phenomena which take place 

 before us are mainly dependent on it. Animals breathe air in order 

 to obtain only oxygen from it, the oxygen entering into their 

 respiratory organs (the lungs of human beings and animals, the gills of 

 fishes, and the trochae of insects) ; they, so to say, drink in air in order 

 to absorb the oxygen. The oxygen of the air (or dissolved in water) 

 passes through the membranes of the respiratory organs into the blood, 

 is retained in it by the blood corpuscles, is transmitted by their 

 means to all parts of the body, aids their transformations, bringing 



1 As regards the interior of the earth, it probably contains far less oxygen compounds 

 than the surface, judging by the accumulated evidences of the earth's origin, of mete- 

 orites, of the earth's density, &c., as set forth in the fourth chapter of my work on the 

 ' Naphtha Industry,' 1877, in speaking of the origin of naphtha. 



