Green’s Dictionary of Slang

(US) extremely strong liquor; also attrib.

1903		Harrisburg Dly Indep. (PA) 19 Dec. 9/3: ‘It was regular third-rail whiskey’.
1908		Eve. Star (Wash., DC) 18 Oct. 57/3: You used to [...] toss down your little two bits for a horrible slug of third-rail booze, or a punkerino bottle of beer.
1917		O.O. McIntyre New York Day by Day 25 Nov. [synd. col.] [On the Bowery] they can live cheaply and and buy five-cent third-rail whiskey.
1919		O.O. McIntyre New York Day by Day 22 Mar. [synd. col.] Even on the Bowery a shot of ‘third rail’ whiskey costs 30 cents.
1925		O.O. McIntyre New York Day by Day 24 Aug. [synd. col.] A place [...] near Chatham Square where third rail whiskey was a nickel a shock.
1926		N. Klein ‘Hobo Lingo’ in AS I:12 653: Third-rail — strong wine.
1928		J. Callahan Man’s Grim Justice 4: He was always after my mother for the price of [...] a shot of third-rail booze.
1930		Pittsburgh Post-Gaz. (PA) 22 Mar. 17/1: You take the case of one former boxer who when he gets squiffed on home brew or Third Rail varnish is not allowed to talk like the ordinary fellow who gets squiffed because if he does the boys tap their domes [...] and recall the day that Charley White tapped him on the koko.
1950		Goldin et al. DAUL 221/2: Third-rail. 1. Strong raw whiskey.
1962		Ragen & Finston World’s Toughest Prison 821: third rail – Strong, cheap liquor.