Re: What does a candle emit when it burns?

Yes, you are correct.  From Wikipedia (http://en.wikipedia.org/wiki/Combustion):

"Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel 
(usually a hydrocarbon) and an oxidant accompanied by the production of heat or both heat and 
light in the form of either a glow or flames, appearance of light flickering."

Because combustion is not 100% efficient, you have a lot of byproducts that are released in the 
reaction.  The black spot you notice is a combination of carbon, unburnt materials, soot, etc.  You 
may also have chemical components, some of which can be toxic.  That's why you should avoid 
smoke (and smoking) whenever possible.