The Collaborative International Dictionary
spirit of salt
Muriatic \Mu`ri*at"ic\, a. [L. muriaticus pickled, from muria brine: cf. F. muriatique.] (Chem.) Of, pertaining to, or obtained from, sea salt, or from chlorine, one of the constituents of sea salt; hydrochloric.
Muriatic acid, hydrochloric acid, HCl; -- formerly called also marine acid, and spirit of salt. See hydrochloric, and the Note under Muriate.
Wiktionary
spirit of salt
n. (context obsolete inorganic compound English) An old name of hydrochloric acid.