112 CHEMISTRY. 



in them. You see that there is twice as much gas in /, the 

 tube containing the hydrogen, as there is in e, the tube con- 

 taining the oxygen; this confirms what we have just stated, 

 viz., that two volumes of hydrogen unite with one volume of 

 oxygen. If, when there is a sufficient amount of the gases 

 collected, you cautiously remove the tube e, closing its mouth 

 with your finger, and, turning it upside down, introduce into 

 it a slip of wood with a spark on the end, the wood will burst 

 into a flame showing that the gas is oxygen. If now you 

 remove/, and apply a light to its mouth, the gas will rush 

 out, burning as it comes. Or, if you mingle with it an equal 

 quantity of atmospheric air, and then apply the light, you 

 will have an explosion. These phenomena are characteris- 

 tic of hydrogen, as you will presently learn. 



The above experiment may be varied. Thus, let P 

 and N, Fig. 36, be tubes with their lower ends open, 

 and having wires of platinum passing through their 

 sealed upper ends. The wine-glasses, the curved tube 

 connecting them, and the two tubes, P and N, are filled 

 with acidulated water. On connecting P with the pos- 

 itive pole, and N with the negative, oxygen gas will 

 collect in P and hydrogen in N, and as readily as they 

 would if the tubes were in one vessel. 



This physical method of decomposing water by a 

 current of electricity has received the name of electrolysis of water. Many 

 substances, particularly liquids, both inorganic and organic, may be decom- 

 posed by submitting them to electrolysis. 



142. Mode of Obtaining Hydrogen. Hydrogen can be ob- 

 tained by a process represented in Fig. 37 (p. 113). A gun- 

 barrel filled with clean iron turnings is placed across the 

 fire in a furnace. Steam, or more properly water-gas, is 

 made to pass through the barrel by means of a glass tube, 

 which conducts from a flask where water is boiling by means 

 of a gas-burner. The water-gas that is, the water in the 

 form of vapor passing among the iron turnings, is decom- 



