Purification of the crude caffeine by sublimation was not performed due to time limitations and technical issues. Under the right conditions, it does work very well! In addition to the description in the Experimental Procedure, see also Technique 9. 

a) What property or properties make caffeine an ideal candidate for sublimation? 

b) How is caffeine separated from impurities during the sublimation procedure? In other words, describe what occurs in the sublimation apparatus – where is the caffeine at the end of the process, where are the impurities at the end of the process, and why?