FIRE A SOURCE OF WATER. 



The outer tube, though it improves the ex- 

 periment by confining the combustion gases 

 and spreading them over the inner tube, is not 

 indispensable. The facts can be shown even 

 by holding a cold knife-blade or piece of glass 

 in a flame for a second, when a deposit of mois- 

 ture will appear on its surface. For this pur- 

 pose it is better not to use an ordinary gas or 

 candle flame, as the cold causes imperfect com- 

 bustion and a deposit of soot, which obscures 

 the effect. 



There is no fact of more common observa- 

 tion than the deposit of moisture from the 

 breath on the inner surface of window panes 

 when the air is very cold outside. The same 

 thing can be observed without anyone breathing 

 in the room, if there are plenty of flames burn- 

 ing there, and discharging the gases of combus- 

 tion into the room (not up the chimney). 



It would appear, then, that moisture is 

 actually produced by and in flames. So it 

 is. Combustion is the rapid, heat-producing 

 combination of substances, chiefly carbon and 

 hydrogen, with the oxygen of the air. Nearly 

 all combustibles are composed of carbon or 

 hydrogen or both, often with other elements as 

 well. When carbon combines with oxygen, the 

 product is carbonic acid, with which we have 

 at present nothing to do. 



The product of the combination of hydro- 

 gen and oxygen is water, and as hydrogen is 



.203 



