178 MOLECULES OF HYDROGEN. 



the process of driving off the other three kinds of 

 molecules by heat. 



The extent to which this process of carboniza- 

 tion has been carried on during the geological 

 heating of our planet is manifest in the vast beds 

 of mineral coal, organized by antediluvian sunshine 

 on the leaves of plants. Indeed, molecules of car- 

 bon, oxygen, hydrogen, and nitrogen, combined 

 by the solar excitation transmitted to the outspread 

 leaves of plants, constitute the substances most es- 

 sential for sustaining life, and those whose posses- 

 sion is prized as individual and national wealth. 



MOLECULES OF HYDROGEN. 



Molecules of pure hydrogen, in the form of gas, 

 rarely exist; being generally found in a state of 

 union with oxygen as water, and with other kinds 

 of molecules. 



It is used in balloons on account of its great 

 buoyancy. A triple alliance of molecules of 

 hydrogen, oxygen, and carbon imparts a wonder- 

 ful diversity of properties to numerous organic 

 substances, as wood, vegetable oil, animal flesh 

 and fat, &c. 



One of the most remarkable changes in the 

 properties of hydrogen molecules is their conver- 

 sion into acids, when united with oxygen ; and 

 into alkaloids, when combined with nitrogen, as 

 in the formation of ammonia. 



Equal measures of hydrogen and chlorine gases, 



