192 SMELLS AND PERFUMES 



the " smells " of chlorine, of bromine, and of iodine from 

 one another. And there are statements current as to the 

 distinctive smells of metals — though they may possibly be 

 due to the action of the metals on organic matter. In any 

 case it seems, according to our present knowledge, that the 

 smell given out by the rubbing of pieces of silica (quartz, 

 flint, etc.) is due to particles of silica (oxide of silicon) 

 volatilised by the heat of friction, which are capable of 

 acting specifically on the olfactory sense-organ. 



