Green’s Dictionary of Slang

jack (a) dandy n.

brandy.

1828		F.F.Cooper Elbow-Shakers! I iv: I will quit the Jack-a-dandy.
1857		‘Ducange Anglicus’ Vulgar Tongue.
1859		Hotten Dict. of Modern Sl. etc. 144: Jack Dandy brandy.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1886		Sporting Times 9 Jan. 5/4: Thirsting for a little Jack the Dandy.
1894		Pall Mall Gaz. 4 July 3/2: No master of the language would ever brandy or gin their primitive names, ‘Jack the Dandy’ or ‘Brian O’Lynn.’ The one is always referred to as ‘Jack’, the other as ‘Brian’.
1902		Dundee Courier 14 June 7/2: ‘Joe and dandy’ means brandy.
1909		J. Ware Passing Eng. of the Victorian Era.
1910		Eve. Teleg. (Dundee) 3 Aug. 4/1: He was having a 'Jack and Rosie' [...] 'Jack-the-Dandy' (brandy), 'Rosie Loader' (soda).
1933		‘William Juniper’ True Drunkard’s Delight.
1960		J. Franklyn Dict. of Rhy. Sl.
1992		R. Puxley Cockney Rabbit.