Green’s Dictionary of Slang

a room in Newgate gaol, dedicated to the imprisonment of debtors, who were known as tangerines.

1708		J. Hall Memoirs (1714) 17: Just by them lye the Tangerines, in a large Room, call’d Tangier, which, next the Lower-ward, is the nastiest Place in the Goal [sic]. The miserable Inhabitants thereof are Debtors.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Tangier A room in Newgate, where debtors were confined, hence caled Tangierines.
1811		Lex. Balatronicum.
1884		A. Griffiths Chronicles of Newgate 97: A second common-side debtors’ room. This came to be called ‘Tangier’ [...] no doubt from the stifling atmosphere.