GLOSSARY 303 



Valence Electrons. Those outer electrons of an 

 atom through the dnect agency of which the atom 

 oombines with other atoms. 



VanH Hoff Factor i. Van't Hoff found that for 

 many very dilute solutions the osmotic pressure is 

 the same as the gaseous pressure which the substance 

 in solution would exert in the gaseous state, at the 

 same absolute temperature and occupying an equal 

 volume. Van't Hoff's law of osmotic pressure states: 

 "Equal volumes of different solutions, at the same 

 temperature and osmotic pressure, contain equal 

 numbers of molecules of dissolved substances." 

 Electrolytes, because of their dissociation into ions, 

 give greater osmotic pressures than non-electrolytes. 

 To bring these anomalous osmotic pressures into 

 harmony with the general finding, van't Hoff 

 introduced the factor i, the value of which is "the 

 ratio of the total number of ions and molecules to 

 the total number of molecules if no dissociation had 

 occurred." See Osmotic Pressure, Electrolyte, and 

 Avogadro Constant. 



Velocity of Light (symbol c). 186,173 miles a 

 second. (Albert A. Michelson's new figures.) All 

 other known velocities are less than that of light; 

 and it is held to be impossible that material veloc- 

 ities can exceed the velocity of light. 



Viscosity. That property of gases, liquids and 

 semi-fluids by reason of which they resist displace- 

 ment, or change of the arrangement, of their con- 

 stituent parts. 



X-rays, Roentgen Rays. Rays that are sent out 

 when a stream of cathode rays (electrons) strikes 

 the opposite walls of a vacuum tube. X-rays are 

 similar to fight. "Today," says Sommerfeld, "we 

 speak of Roentgen-light, and distinguish it from 

 visible light only through its greater hardness (pene- 



