62 



PHYSIOLOGY. 



Fig. 6s- 

 Apparatus for col- 

 cting quantity of 

 oxygen from elodea. 



The funnel should be one with a short tube, or the vessel one 

 which is quite deep so that a small test tube which is filled with 

 water may in this condition be inverted over the 

 opening of the funnel tube. With this arrange- 

 ment of the experiment the gas will rise in the 

 inverted test tube, slowly displace a portion of 

 the water, and become collected in a sufficient 

 quantity to afford us a test. When a consider- 

 able quantity has accumulated in the test tube, we 

 may close the end of the tube in the water with 

 the thumb, lift it from the water and invert. 

 The gas will rise against the thumb. A dry lecti ' n s quantity of 



' oxygen from elo 



soft pine splinter should be then lighted, and (D 



after it has burned a short time, extinguish the flame by blowing 



upon it, when the still burning end of the splinter should be 



brought to the mouth of the tube as the thumb is quickly moved 



to one side. The glowing of the splinter shows that the gas is 



oxygen. 



128. It is better to allow the apparatus to stand several days 



in the sunlight in order to 

 catch a full tube of the gas. 

 Or on a sunny day carbon 

 dioxide gas can be led into 

 the water in the jar from 

 a generator, such an one 

 used for the evolution of 

 The CO 2 can be produced 

 by the action of hydrochloric acid 

 on bits of marble. The CO 2 

 should not be run below, the fun- 

 nel. The test-tube should be 

 fastened so that the light oxygen 

 gas will not raise it off the fun- 

 nel. With the tube full of gas the 

 test for pxygen can be made by 

 lifting the tube with one hand and 



Fig. 66. 

 Ready to see what the gas 



