Green’s Dictionary of Slang

(US) an alcoholic drink; thus in one’s element, intoxicated.

1737		B. Franklin ‘Drinkers Dictionary’ in Pennsylvania Gazette 6 Jan. in AS XII:2 91: They come to be well understood to signify plainly that A MAN IS DRUNK. [...] In his Element.
1855		W.G. Simms Forayers 241: ‘I hope you were sober, sir.’ [...] ‘Oh! yes—couldn’t be otherwise, sir; at that time hadn’t drank a thimbleful of the element.’.