AND AGRICULTURE. 19 



is removed, they resume their original volume. 

 The Germans first called these elements gases, 

 which meant ghosts, because they could not be 

 seen ; they were once supposed to be the soul or 

 spirit of solid matter. 



A great many vegetable substances do not 

 contain all the four elementary bodies named 

 and described, but only three of them, namely, 

 carbon, hydrogen and oxygen; all the bodies 

 which contain no nitrogen are called non-azot- 

 ized substances. 



Starch, sugar, gum, woody fibre, oils and 

 fats, are among the most common of the non- 

 azotized bodies, or those which contain only car- 

 bon, hydrogen and oxygen. Substances which 

 contain nitrogen are called azotized. 



Eight or ten different substances are found in 

 the inorganic part of plants : these are potash, 

 soda, lime, magnesia, oxide of iron, oxide of 



Questions. What do the gases do if the pressure is 

 removed ? Are all the four preceding elements found in 

 vegetable substances ? Which is not found in a great many ? 

 Name some of the most common in which nitrogen is not 

 found. What are those called which contain no nitrogen ? 

 What those which contain nitrogen? How many sub- 

 stances are found in the inorganic part of plants ? Name 

 them. 



