PREPARATION OF HYDROGEN. 



225 



the cork of a second smaller glass bottle, and reaches in this also 

 nearly to the bottom. The cork of the smaller bottle has also a 

 second hole through which a short glass tube r passes, which is best 

 bent at right angles close to the cork. The corks should be care- 

 fully chosen, well softened by hammering, and neatly bored; no 

 luting should be used for them, as they have to be removed every 

 time that gas is to be generated. The smaller vessel serves for puri- 

 fying the generated gas ; for the present purpose it is loosely filled 

 cotton wool, which retains the small liquid particles which are 



FIG. 154 (| real size). 



Fio. 155 (f real size). 



carried away by the gas while escaping from the generating bottle. 

 About 50s r of zinc in small pieces are thrown into the large bottle ; 

 the india-rubber tube for conveying the gas is passed over the 

 end of the tube r, the whole is put together, and the dilute acid is 

 finally poured into the bottle through the funnel tube t. 



The escape of gas is at first rather slow, but the action soon 

 becomes very lively and is accompanied by brisk effervescence, the 

 frothing liquid rising in the bottle ; the dilute acid should therefore 

 be poured in very gradually, lest the liquid should pass into the 

 smaller vessel. When the action subsides, a little more dilute acid 

 is poured into the bottle. The generation of the gas should be 

 allowed to proceed for some time, before filling soap-bubbles with 

 it, in order that the air which originally filled all parts of the 

 apparatus may be completely displaced by hydrogen. The mouth 

 of the pipe or funnel should be dipped into the soap-water for a 

 very short time only ; if kept too long, a bubble is formed, which, 

 on lifting the mouth of the funnel out of the solution, is deposited 

 upon the surface of it and remains there. The escape of the gas 



Q 



