PROPERTIES OF HYDROGEN. 25 



But the quantity of tliis substance which is stored up in the solid rocks 

 is still more remarkable. Nearly one-half of the weight, of the solid 

 rocks which compose the crust of our globe, of every solid substance we 

 see around us — of the houses in which we live, and of the stones on 

 which we tread — of the soils which you daily cultivate, and much more 

 than one-half by weight of the bodies of all living animals and plants, 

 consist of this elementary body oxygen, known to us, as I have already 

 said, only in the state of a gas. It may not appear surprising that any 

 one elementary substance should have been formed by the Creator in 

 such abundance as to constitute nearly one-half by weight of the entire 

 crust of our globe, but it must strike you as remarkable, that this should 

 also be the element on the presence of which all animal life depends — 

 and as nothing less than wonderful, that a substance which we know 

 only in the state of thin air, should, by some wonderful mechanism, be 

 bound up and imprisoned in such vast stores in the solid mountains of 

 the globe, be destined to pervade and refresh all nature in the form of 

 water, and to beautify and adorn the earth in the solid parts of animals 

 and plants. But all nature is full of similar wonders, and every step 

 you advance in the study of the principles of the art by which you live, 

 you will not fail to mark the united skill and bounty of the same great 

 Contriver. 



Oxygen gas is heavier than common air in the proportion of about 11 

 to 10 [its specific gravity by experiment is 1-1026, air being 1] ; it is 

 also capable of being absorbed by water to a certain extent. One hun- 

 dred measures of water dissolve 6i of this gas. [De Saussure. Ac- 

 cording to Dr. Henry, 100 volumes of water absorb only 3^ of oxygen.] 

 Rain, spring, and river waters, alwaj-s contain a portion of oxygen 

 which they have derived from the atmosphere, and this oxygen, as they 

 trickle through the soil, ministers to the growth and nourishment of plants 

 in vaAous ways. Some of these will be explained in a subsequent lecture. 



In an atmosphere of pure oxygen gas, plants refuse to vegetate, and 

 speedily perish. 



§ 4.' Hydrogen — its properties and relations to vegetable life. 



Hydrogen is also known to us only in the state of gas, and when per 

 fectly pure agrees wiih oxygen and common air in being without colour, 

 taste, or smell. It is not known to occur in nature in a free or simple 

 state, nor does it exist so abundantly as either carbon or oxygen. It 

 forms a small per centage of the weight of all animal and vegetable 

 substances, and constitutes one-ninth of the weight of water, but with 

 the exception of coal, it does not enter as a constituent into any of the large 

 mineral masses that exist in the crust of the globe. 



When a lighted taper is plunged into this gas it is immediately ex- 

 tinguished, but if in contact with the air the gas itself takes fire and burns 

 with a pale yellow flame. If previously mixed with air or with oxygen 

 gas, it liindles and burns with a loud explosion. During this combus- 

 tion water is formed. [See the Second Lecture.] 



It does not support life, animals cease to breathe when introduced into 

 it, and plants gradually wither and die. It is the lightest of all known 

 substances, being about 14^ times lighter than common air, so that if the 

 stopper be removed from a bottle in which it is contained it almost irame- 



