Green’s Dictionary of Slang

crackskull n.

(US) whisky.

1842		Spirit of the Times (N.Y.) (Sept. 17) 341: Sufficient to debar his fellow beings from the use of the ‘crack-skull,’ i.e., whiskey [...] a quart of real crackskull [HDAS].
1956		S. Longstreet Real Jazz Old and New 103: And the piano chords rode up and down and somebody ran out to get another bottle of crackskull. And the chippie he was dating hitched up her rolled stockings and said, ‘Play it, Daddy’ [W&F].