Green’s Dictionary of Slang

1. (US) someone who has spent a long time in the American West.

1904		Wash. Post 25 Dec. 12/5: ‘In this country,’ said an old ‘alkali’ [...] ‘you kin see farther and see less than in any other country in the world.’.
1907		S.E. White Arizona Nights 24: A white-faced woman, who looked mighty good to us alkalis, opened the flap. [Ibid.] 55: And yet an old ‘alkali’ is never happy anywhere else.
1914		Ade ‘The New Fable of the Private Agitator’ Ade’s Fables 18: Some Alkali Statesman of the New School would arise in his Place and give our Hero a Turning-Over.
1921		Eve. Star (Wash., DC) 16 Oct. 88/1: [cartoon caption] This is Alkali Ike!
1993		W. Blevins Dict. of the Amer. West 5/2: Alakali (2) A fellow who’s been in the country for a long time.

2. (US) the experience of living in the West as a quality.

a.1858		‘Sweet Betsy From Pike’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 217: Said a Pike County miner, ‘Will you dance with me?’ ‘Oh! yes,’ said Sweet Betsy, ‘if you don’t make too free; / If you want to know the reason why, / Doggone ye, I’m chock full of strong alkali.’.
1927		C.M. Russell Trails Plowed Under 179: I’m clothed from heel to chin in clothes grimed with sweat and alkali dust; but bein’ civilized, I’m forced to stand it.