16 GENERAL PROPERTIES OF LIVING TISSUES 



cules strike against the liquid. As the speed 

 of the molecules and therefore their power to 

 escape from the liquid rises with the tempera- 

 ture, the vapc^ pressure will also rise with the 

 temperature. 



Solution of a gas in a liquid. A liquid 

 brought near a gas is struck by many of the 

 moving molecules of the gas. Some of these are 

 held by the attractive force of the liquid. Some 

 will at length escape. Finally, as the number 

 of molecules striking the surface of the liquid 

 remains constant at the same pressure, the gas 

 molecules leaving the liquid will equal the number 

 entering (saturation). 



Solution of a solid in a liquid. When a crys- 

 talline solid is placed in a liquid solvent, particles 

 escape from the solid and enter the liquid. Some 

 of these particles again enter the solid and are 

 bound by it. Saturation is reached when the 

 number of particles entering and leaving the 

 solid is equal. 



Solution tension. The force with which the 

 particles of the solid pass into the solvent is 

 termed the solution tension. There is equili- 

 brium, i. e. saturation, when the solution tension 

 is balanced by the force with which the particles 

 in the solvent return to the solid. 



Osmotic Pressure. It has been found that 



