premise: The thermal exchange of <mask> between * * f and liquid * * f is readily measurable at temperatures in the range of 180 ` and above .
hypothesis: the proper context for <mask> here should be a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)