Hot as a coal. The expression has an obvious allusion
To post the coal
To pay or put down the cash. Coal=money has been in
use in the sporting world for very many years. Buxton, in 1863, used
the phrase “post the coal,” and since then it has been in frequent use.
Probably rhyming slang “Coal,” an imperfect rhyme of gool
page 248, Chivy and page 266, Coaling)
“It would not suit me to write, ... even if they offered, ..., to
post the cole.” —Hood.
Burnt brandy The ancient way to set brandy on fire was to drop in
it a live or red-hot coal.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894