THE PLANT. 21 



electrical fluid over the charcoal it mav be ignited, 



* O 



when it will burn with great brilliancy. In burning 

 it unites with the oxygen forming carbonic acid, and 

 disappears. It is no more lost, however, than is the 

 carl >on of wood which is burned in a stove; al- 

 though invisible, it is still in the tube, and may be 

 detected by careful weighing. A more satisfactory 

 proof of its presence may be obtained by decompos- 

 in<l the carbonic acid by drawing the wires a short 

 distance apart, and giving a *jif '//, of electricity. 

 This immediately separates the oxygen from the car- 

 bon, which forms a dense black smoke in the tube. 

 By pushing the corks together we may obtain a 

 wafer of charcoal of the same weight as the piece 

 introduced. In this experiment we have changed 

 carbon from its solid form to an invisible gas and 

 back again to a solid, thus fully representing the 

 continual changes of this substance in the destruc- 

 tion of organic matter and the growth of plants. 



CHAPTER III. 



HYDROGEN, OXYGEN AND NITROGEN. 

 HYDROGEN AXD OXYGEN. 



LET us now consider the three gases, hydarogen^oaBygien t 

 and nitrogen, which constitute the remainder of the 

 atmospheric part of plants. 



