GAS GENERATORS. 109 



chloric acid gas in water, usually sold strong enough to fume 

 visibly on taking the stopper out of the bottle) with three or four 

 times its bulk of water, and pour a little of the diluted acid into 

 the bottle through the funnel. As soon as the liquid comes in 

 contact with the 

 marble a vigorous 

 effervescence will 

 take place ; the 

 marble dissolves as 

 in Expt. 99, only 

 now, owing to the 

 construction of the 

 apparatus, the gas 

 can only escape 

 through the deli- 

 very pipe. When 

 the evolution of gas 

 slackens it can be 

 renewed by pouring 

 a little more acid in 

 down the funnel 

 tube. 



Expt. 101. To 

 illustrate the 



bon Dioxide In Fig> 57< Collectin S Carbon Dioxide b ? Displacement. 

 Expt. 75 we have seen that ammonia gas, being lighter than 

 air, can be collected by displacement, the collecting jar being held 

 mouth downwards ; carbon dioxide, being heavier than air, can 

 be also collected by displacement, but in this case the jar must 

 be held mouth upwards. In order to collect the gas thus arrange 

 the delivery tube of a carbon dioxide generator so as to pass to 

 the bottom of a gas jar standing on the table mouth upwards (fig. 

 57) ; the air in the jar will be displaced by the heavier carbon 

 dioxide, so that after a little while a lighted candle, lowered into 

 the jar by means of a wire, will be extinguished, as in Expt. 71. 

 Place a bit of lighted candle at the bottom of a second wide jar ; 

 the candle will keep on burning (unless the jar be too narrow). 

 Pour into this jar the gaseous contents of the first jar, holding it 

 just as though it were full of water (fig. 58) ; although the falling 

 of the heavier carbon dioxide into the jar is not visible directly 

 to the eye, yet the passage is at once rendered evident by the 

 extinguishing of the candle. 



Expt. 102. Another Illustration Obtain a large wide glass 



