48 



the aqueous tension is 16 mm. The pressure of the gas alone is 

 therefore 752 16 = 736 mm. The fully corrected volume = 



175 x 1 x m - mA c - c - 



Molecular Hypothesis. The relations between pressure and 

 volume (Boyle's law) and between either of these and temper- 

 ature (Charles' law) in gases may be explained by the molecular 

 hypothesis. According to this idea, all matter is composed of 

 minute particles called molecules, those of any given substance 

 being all alike in nature and in mass. 



In solids and liquids these molecules are closely packed 

 together. In gases, however, they are widely scattered, with 

 much vacant space between them. A gas is in fact a vacuum, 

 with numerous relatively minute particles scattered through it. 

 When a gas is compressed, only the spaces between the molecules 

 are reduced. By assuming further that, in gases, the molecules 

 are in rapid motion, and produce pressure by striking the walls 

 of the vessel, and that this motion is increased by raising 

 the temperature, all the laws of gases can be completely explained 

 (see p. 88-93). , 



Exercises. 1. Show that, if the levels of the water inside and 

 outside the tube (Fig. 15, p. 26) are equal, the pressure of the gas 

 inside must be equal to the atmospheric pressure. 



2. Find the volume that 48 c.c. of gas at 732 mm. would occupy 

 at 760 mm. 



3. Reduce 48 c.c. of gas at 780 mm. to standard pressure 

 (760 mm.). 



4. Find the volume which 28 c.c. of gas at 775 mm. would 

 occupy if the pressure changed to 730 mm. 



5. Find the volume which 320 c.c. of gas at 20 would occupy 

 at (pressure unaltered). 



6. Reduce 600 c.c. at 25 and 760 mm. to standard conditions 

 (0 and 760 mm.). 



