Fuller’s earth, n.¹ — Green’s Dictionary of Slang

Fuller’s earth n.¹

[SE Fuller’s earth, ‘a hydrous silicate of alumina, used in cleansing cloth’ (OED); thus gin is a scourer and ‘cleaner out’]

gin.

1819		Egan Key to the Picture of the Fancy going to a Fight 9: [note] The Out and Outers, from the addition of bitters to it, in order to sharpen up a dissipated and damaged Victualling Office cannot take any thing but ‘Fuller’s Earth’.
1821		‘An Amateur’ Real Life in London I 394: The Swell Covies and Out and Outers find nothing so refreshing after a night’s spree, when the victualling-office is out of order, as a little Fuller’s-earth, or a dose of Daffy’s.
1832		Egan Bk of Sports 70: [as 1819].
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1890		C. Hindley Vocab. and Gloss. in True Hist. of Tom and Jerry 176: Fuller’s Earth. Another of the thousand endearing names for the universal favourite gin!