32 



Elementary Plant Physiology. 



second bottle and nearly to its bottom. The second bottle 

 should be filled to a depth of about six to eight centimeters 

 with a solution of potassium permanganate, and should be 

 provided with an outlet tube to which may be attached suit- 

 able connections for filling the retort containing the seedlings. 

 When all is in readiness, pour hydrochloric acid in the funnel 

 or thistle tube until the zinc is covered to some depth with the 

 liquid. A mixture of one part sulphuric acid and six parts 



of water may be used 

 instead of hydro- 

 chloric acid. A rapid 

 evolution of hydrogen 

 gas should ensue im- 

 mediately, and after 

 two or three minutes 

 all of the air will 

 have been expelled 

 from the apparatus, 

 and the hydrogen pass- 

 ing off through the wash 

 bottle will be purified 

 by the potassium per- 

 manganate solution. 

 Run the tip of the 

 outlet connection un- 

 der the opening of the retort or respiration tube, and fill it 

 with the gas. 



Carbon dioxide may be generated in the apparatus described 

 above, using fragments of marble instead of zinc, and ordi- 

 nary hydrochloric or muriatic acid. Some care will be neces- 

 sary to make all the fittings proof against leakage of gas. After 

 a sufficient supply of gas has been produced, the acid should be 

 poured out and the zinc or marble well washed in water. 



The following form of generator may be found more conve- 



Fig. 17. — Apparatus for generation of hydrogen. 

 Ay wash bottle containing solution of potassium 

 permanganate. 



