Green’s Dictionary of Slang

a mouth and throat parched through excessive drinking; thus, a hangover; thus cool the coppers, to consume a (supposed) hangover cure; cit. 1909 refers to a dry throat from excessive talk; hot is implied in cit. 1863.

1805		J. Davis Post Captain (1813) 5: ‘I [...] was compelled to rise at midnight, and drink a glass of cold water.’ ‘Damnable [...] then your coppers were hot’.
1830		Egan Finish to the Adventures of Tom and Jerry (1889) 135: The ‘uncommonly big gentleman’ in spite of swallowing oceans of soda-water, declared ‘his copper’ to be so hot that he thought all the water in the sea could not reduce his thirst!
1841		Punch I 244: Oh blow your physiology! [...] You mean to say you’ve got a hot copper – so have I. Send for the precious balm and then fire away.
1850		Thackeray Pendennis II 42: Nothing like that beer, [...] when the coppers are hot.
1852		Exeter & Plymouth Gaz. 14 Aug. 6/2: No more headaches [...] no more cool claret and hot coppers.
1861		Hills & Plains I 38: ‘Hot coppers are the devil [...] Have one of my “doctors” now; it will do you no end of good’.
1863		T. Taylor Ticket-Of-Leave Man Act IV: Suppose we begin with a brandy and soda, to cool the coppers!
1866		Sportsman 13 Oct. 2/1: Notes on News [...] ‘A hair of the (spirituous) dog that bit you’ is [...] said to be a good cure for ‘hot coppers’ [...] the morning after a ‘wet’ night.
1870		Hotten Sl. Dict.
1881		Bulletin (Sydney) 19 Feb. 8/4: She served him with the best of brands, / From bottles with glass stoppers, / When – like weak mortals – of a morn / That brave ‘cop.’ had ‘hot coppers.’.
1881		Nat. Police Gaz. (NY) 29 Oct. 4/1: [headline] he wanted a drink And Got the Very best remedy for Hot coppers which Science can Devise.
1890		Sporting Times 31 May 2/5: There are two heroes [...] in the village who complained hof hot coppers in the morning.
1892		H. Nisbet Bushranger’s Sweetheart 134: As happy-looking and lively as if no such thing as hot coppers existed, nor dry throats.
1900		Bulletin (Sydney) 27 Jan. 15/1: Early next morning, when ‘coppers’ might be expected to be very ‘hot,’ shanty-keeper No.1 filled an empty barrel with water and left his cabin for a few minutes.
1902		Ade ‘R-E-M-O-R-S-E’ in Verses and Jingles (1911) 2: To-day I feel like thirty cents. / My eyes are bleared, my coppers hot, / I’ll try to eat, but I cannot.
a.1909		press cutting in J. Ware Passing Eng. of the Victorian Era 20/2: Let ’em say what they like, and howl themselves dotty. Their barrikin only makes ’em thirsty and when they’ve got hot coppers through chucking the barrikin out too blooming strong, they go in for a little quiet booze themselves, make no error.