3 Heat Is Also Lost by Radiation
This takes place less rapidly from a bright, highly polished surface, and for this reason “Thermos” and similar bottles are encased in polished nickle. A cooker-pail with polished outside surface retains heat better than one with a dull finish. In those cookers made with a metal outside retainer, the surface should not be painted or roughened or dulled by any means.
Experiment: Radiation
Take two empty tin cans of the same size and shape. Wash off the paper labels. Keep one of them bright and shining, but move the other through a candle flame until the entire outer surface is smoked. Into each pour exactly the same quantity of water at the same temperature. Note carefully the temperature and the time. At the end of any given period, say one hour, again take the temperature of each. Which has lost the most heat, that in the bright can or that in the dull can?