So there I was, try all kinds of librarian ninja tricks on the fanciest, most expensive research databases money can buy (SciFinder, Reaxys, Inspec...) and no joy. Couldn't find what I needed. I'm perfectly willing to admit that I don't know all that much chemistry, but usually I do ok since I work with one chemist quite a bit. Finally I gave up and googled it. After a few tries, I found way down in the results an article about something else (like I needed a chemical in an aqueous solution and it had the chemical in alcohol), but the snippet drew my eye. Sure enough - had a table with my data in it. An ACS journal from 1945.
The data I needed were not the focus of the paper - they were there sort of as a calibration or reference type thingy - to show what the setup would do with no alcohol. So it's absolutely right that the document wouldn't have come up in my search, because technically the article didn't match. That's why the full text search worked.
It could be that I could locate the info using SpringerImages (but it's an ACS article) or using CSA's deep indexing (is illustrata still around? I did try Aerospace & High Tech). Lesson learned.