322 APPENDIX 



sufficient granulated zinc into the bottle to completely cover the 

 bottom. Replace the cork, pour enough water into the bottle to 

 seal off the lower end of the funnel-tube. Add strong hydrochloric 

 acid, a little at a time, and in such a manner that air-bubbles shall 

 not be carried down with it. Whenever the evolution of the gas 

 becomes less brisk, more acid should be added. 



CAUTION: No flame should be allowed anywhere near a hydrogen generator 

 until gas has been evolving briskly for at least five minutes ! ! Do not actually apply 

 a flame to any portion of the apparatus, until a test, according to Exp. 1, shall have 

 proved the absence of an explosive mixture ! 



EXPERIMENT 1. To test whether air has been entirely displaced 

 by hydrogen: Pour so much water into the "pneumatic trough " 

 that the perforated shelf is well covered. Immerse a test tube until 

 it is quite full of water; raise the closed end out of the water, and 

 rest the tube with its opened end upon the shelf. Bring the delivery- 

 tube of the gas generator into such a position that the escaping 

 bubbles rise into the test-tube and displace the water contained in 

 it. When the tube is quite full of gas, close it with your thumb and 

 carry it to a lighted burner, not removing your thumb until the 

 mouth of the tube is close to the flame. If the gas lights with a faint 

 sound, and the flame works its way quietly down the tube, no air 

 was mixed with the hydrogen in the generator; but, if the gas 

 burns all at once, with more or less of an explosion, air was still con- 

 tained in the generator at the time the sample was taken. Repeat 

 the experiment, until a sample burns quietly. 



NOTE that this experiment must be repeated every time that the generator is set 

 up afresh. The small volume and the thin walls of the test-tubes make these ex- 

 plosions harmless, whereas a similar explosion in the generator might lead to danger- 

 ous injuries. 



EXP. 2. To compare the density of hydrogen with that of air. 

 Fill two test-tubes over the pneumatic trough with hydrogen: 

 hold one, mouth up, for ten seconds, then approach the mouth 

 to the flame; hold the other, mouth down, for ten seconds, and 

 approach to the flame. Note and explain any difference. 



EXP. 3. Connect the inner tube of the "osmose-apparatus" 

 with the hydrogen generator, by means of a bit of rubber tube. 

 The pipe-bowl will be filled with hydrogen in a little more than two 

 minutes. Pull out the inner tube and set the open end of the outer 



