55 



80. Besides these saline and earthy substances, 

 •water always contains atmospheric air dissolved in it. 

 This is essential to the life of fishes, and to the growth 

 of water-plants, which could not exist if they were 

 not thus supplied with common air. 



81. Water is essential to the existence of all plants 

 and animals : it constitutes a large proportion of all 

 animal and vegetable substances, it is the principal 

 component of -the blood of animals, and the sap of 

 plants, and is of the greatest importance, as being 

 the means of introducing into their systems many 

 soluble matters, necessary for their healthy growth. 



82. Hydrogen, the inflammable element of water, 

 is a substance of considerable interest ; it is true, it is 

 never found in Nature in a pure and separate state, 

 but its compounds are abundant, and some of them 

 very important ; w^hen pure, hydrogen is an invisible 

 transparent gas, like the air; very combustible, burn- 

 ing readily when once inflamed, and remarkable for 

 being so much lighter than common air, that a thin 

 bladder, filled with this gas, would rise through the 



