Lightin' a fart (really!)

[drollman]

Here’s one from “The Nephew Files”:
What is the difference between the gas we pass by burping and the gas by pass by farting? You can ignite a fart, but you can’t ignite a burp, what are the differences between the two? Thanks: DJ (Drollman’s Nephew!)

[mangeorge]

I think that a burp is usually air. Read that somewhere.
Peace,
mangeorge

[dtilque]

Cecil has covered this indirectly: http://www.straightdope.com/classics/a1_079.html

Intestinal gas, we learn, is made up mostly of five gases: nitrogen, oxygen, carbon dioxide, hydrogen, and methane. The first two you get from swallowing air during eating, while the last three are generated in the large intestine. From this we may deduce that burps and belches, which emanate from the stomach, consist mostly of air.

Note that two of the gasses that make up a fart are flamable. And this is probably where mangeorge read about belches being mostly air.