E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Small combustible bodies blazing at one end and floating in a glass of liquor. The liquor was stirred about with a candle-end to promote combustion. A skilful toper would swallow them blazing, as we swallow the blazing raisins of snap-dragons.
He drinks off candles ends for flap-dragons.Shakespeare: 2 Henry IV., ii. 4.