THE COMPOSITION <>F WATKK. HYDROGEN 



125 



escaping through it. The gas escapes through a special gas-conducting 

 tube, which is firmly tixctl. by a cork, into the other neck, and which 

 ids in a water bath (fig. 20), under the orifice of a glass cylinder full 



FIG. 20. Apparatus for the preparation of hydrogen from zinc and sulphuric acid. 



of water. 16 If sulphuric acid be now poured into the W.oulfe's bottle, 

 it will soon be seen that bubbles of a gas are evolved, which is hydrogen. 



lti As laboratory experiments with gases require a certain preliminary knowledge, we 

 will describe certain practical methods for the preparation and collection of gases. 

 When in laboratory practice an intermittent supply of hydrogen (or other gas which is 

 evolved without the aid of heat) is required the apparatus represented in fig. 21 is the 



FIG. 21. A very convenient apparatus for the preparation of gases obtained without heat. It may 

 also replace an aspirator or gasometer. 



most convenient. It consists of two bottles, having orifices at the bottom, in which 

 corks with tubes are placed, and these tubes are connected by an india-rubber tube 

 (sometimes furnished with a spring clamp). Zinc is placed in one bottle, and dilute sul- 



