I have come across "pass off in vapor" or "pass off in fumes" at several places. But I can't seem to find the corresponding definition of "pass off" that would fit in the context.

The definitions of "pass off", to sum up Merriam Webster and The Free Dictionary, are either to misrepresent something (used transitively), or to carry out (used intransitively).

But neither definition seems to sufficiently explain the following sentences, where the phrase seems to carry the meaning of "evaporate". In fact, MW defines words like "evaporate" and "volatilize" as "pass off in vapor". The meaning of the phrase is pretty obvious, but I just can't find the definition.

Example sentences (from Google books):

The latter plate, being perforated, permits the oil to thence pass onto the next lower ball,and so on downward until it is volatilized and passed off in vapor.

Hydrogen unites with more oxygen to form water, which is passed off in vapor from the lungs, in perspiration from the skin, and in urine from the kidneys.

  • It really means to disappear through evaporation, but, like you, I cannot find a definition. – Mick Nov 14 '17 at 9:02

The OED says (meaning 2b):

intr. Of a vapour or other substance: to leave or come away from, esp. by evaporation. Also fig. Now rare.

with citations from 1791 to 1939.

I would call it obsolete. I've can't find a single instance of this use in COCA (Corpus of Contemporary American English) or the British National Corpus, and the latest example I could find in COHA (Corpus of Historical American English) was from 1910.

  • OIC! That's why I can hardly find anything on Google Books from recent decades. Thanks. – Eddie Kal Nov 14 '17 at 18:45

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