46 LABORATORY LESSONS IN GENERAL SCIENCE 



another bottle inside with strong ammonia water and let it 

 drain. 



Both these liquids are solutions of gases in water. The 

 bottles are thus made to contain in one case hydrochloric 

 acid gas and in the other ammonia gas. In both cases these 

 are mixed, of course, with much air. Observe any color or 

 other evidence of the presence of the gases in the bottles. 



When these gases combine chemically they form particles 

 of a white solid easily seen. This change can occur only 

 where there is intimate contact of the gases. 



Now bring the mouths of the bottles together, holding 

 both horizontally. Note the progress of the chemical 

 change, and explain the mixing of the gases as the bottles 

 are held in place. 1 



OSMOSIS IN THE BODY AND IN PLANTS 



Watch closely while the teacher sets up the apparatus as directed 

 below, noting the results that manifest themselves through a con- 

 siderable period of time afterward : Fill with 

 molasses a "diffusion bulb" that has been 

 thoroughly soaked for a time in hot water, and 

 insert into its mouth a close-fitting rubber stop- 

 per through which has been passed a rather 

 long glass tube of small bore. Twist a wire 

 tight around the top of the bulb to prevent 

 any leakage around the stopper. Set the bulb 

 and its tube down into a bottle of water deep 



1 The striking change in the substances here is 

 indeed a phenomenon. In science any change in 

 matter, however familiar it may be, is considered 

 a phenomenon, and is evidence of the action of some 

 force. All the changes of the preceding experiments 

 of this lesson are illustrations of phenomena. 



FIG. 19. Osmosis 

 apparatus for liquids. 



