SCIOPTICON MANUAL. 



175 



able heat is produced in making tbe mixture, and for 

 this reason it should be made beforeband in an earthen- 

 ware, not a glass vessel, so as to allow sufficient time for 

 it to become cool before being added to the granulated 

 zinc contained in the generator a (Fig. 47). 



b 



Fly. 47 



About two pounds of zinc is introduced into tbe 

 generator (a glass bottle to hold five gallons or more, 

 or a vessel made of lead), the top of which, bearing the 

 tube funnel and bent exit tube, is then replaced, and the 

 joint being made airtighfT^Ih the case of a leaden gene- 

 rator by means of a screw, and in the case of a glass 

 bottle, by a metallic stopper coated with rubber), the 

 diluted acid is poured down the long tube funnel 6, the 

 end of wbich descends far enough into the liquid to 

 prevent the return of gas in tbat direction. A brisk 

 action ensues, the gas effervescing like so much soda- 

 water. The first portions should, however, be allowed 

 to escape for some minutes at the outlet of the wash 

 bottle c, to expel tbe air. To ascertain when hydrogen 

 begins to flow, we might apply a light to soap-bubbles 



