y -.-X^ 



TOBACCO 



TAR 



~ * • ■ ' A 



.V ■ 



CHIMNEY 

 SOOT 



J 



SCORCHED 

 BREAD 



X-IRRADIATED 

 BREAD 



Fig. 1. Microwave electron spin resonances of radicals in some common 

 substances. The tobacco tar was taken from an old pipe stem. Coal, wood, and 

 other tars give similar resonances. The chimney soot was taken from the flue of 

 an oil-burning furnace. Similar resonances were obtained for soot taken from the 

 exhaust pipe of an automobile and from a wood-burning fireplace. Ordinary 

 bread, unscorched and not irradiated, gave no detectable resonance in the same 



spectrometer. 



to face p. 354 



