The Chemical Relations of Water 297 



discontinued, the water should not rise in the glass tube. 

 Having secured a satisfactory result, remove the glass 

 tube. Pass hydrogen through the apparatus slowly 

 so that the bubbles rise in the sulphuric acid at 

 the rate of about two per second. Collect a sample 

 of the gas issuing from the calcium chloride tube and 

 test its character by lighting it. As soon as the sample 

 burns quietly, light the Bunsen burner underneath the 

 hard glass bulb. The oxide should be raised to a dull 

 red heat. Continue the passage of the gas until the 

 oxide has assumed a brownish-red tint and an appreci- 

 able quantity ,of water has collected in the smaller 

 bulb. Turn out the burner, and let the apparatus 

 cool. In exact work, a stream of dry air is passed 

 through the apparatus by disconnecting the hydrogen 

 generator, and replacing it by a gas-holder containing 

 air, the air being sent through for two or three minutes 

 at about the same rate as in the case of the hydrogen. 



Exercise for Student. 



Why is this passage of dry air necessary for an exact determina- 

 tion to be effected ? 



When quite cool, the portions previously weighed 

 are again weighed separately. The gain in weight of 

 the absorbent portion is that of the water formed as 

 the result of the action of the hydrogen on the hot 

 oxide. The loss of weight of the combustion tube 

 and oxide is the weight of oxygen which combined 

 with the hydrogen to form this water. The weight 

 of the hydrogen may be obtained by finding the differ- 

 ence between the weight of water formed and the weight 

 of oxygen contained in it. 



The value of the ratio ^ f *l 8 -- should be 

 weight of hydrogen 



