it must be the Fifties, or maybe even the late Forties, well before Google et al.
1948; see the link Faldage provided. Unfortunately, that link gives only a review, not the full text. Other url's (per brief googling), though also lacking full text, give a bit more of the flavor.

but I can tell you what it is, according to Asimov:
w-doc, my recall differs on some important details. Perhaps there as two or more spoofs, involving variants of the mythical substance?