Green’s Dictionary of Slang

(UK Und.) the practice of deliberately burning the body with a mixture of acids and gunpowder in order to simulate scars and wounds that should soften the hearts of those from whom one begs.

1845		Morn. Post 29 Mar. 7/2: There is no less than seven young men who has lost the use of their limbs for life [...] going about on the scaldrum gag.
1858		A. Mayhew Paved with Gold 267: ‘Hav the scaldrum dodge been worked much?’ asked the cadger, referring to the art of mutilating the body to make the limbs appear as if they had been injured by fire.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 244/2: Peter was initiated into the ‘scaldrum dodge,’ or the art of burning the body with a mixture of acids and gunpowder, so as to suit the hues and complexions of the accident to be deplored. [Ibid.] IV 24: Having real or pretended sores, vulgarly known as the ‘scaldrum dodge.’.
1861		Melbourne Punch ‘City Police Court’ 3 Oct. 234/1: The Mayor.- Well my flying sawney hunter, I think I twigged you on the scaldrum dodge once, and just before that, you were reported to me as being scammered with some multee kertever flue fakers in a flatty ken.
1865		St James’s Mag. 12 251: The scaldrum dodge is an artifice, however, of recent adoption. It is an imitation of sores upon the skin, by the application of soap and vinegar.
1873		Sl. Dict. 278: Scaldrum dodge a dodge in use among begging impostors of burning the body with a mixture of acids and gunpowder, so as to suit the hues and complexions of any accident to be deplored by a confiding public.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1902		H. Baumann Londinismen (2nd edn).