If the air is dry, evaporation is quite rapid even when water is cool. Thus, when water is placed in a slightly porous unglazed earthen vessel, a small amount constantly filters to the outside and evaporates, keeping the contents several degrees cooler than the surrounding air. This device in various forms has been used for hundreds and perhaps thousands of years.

* U. S. Bur. Standards, Circ. 55.

Fireless Cooker

A fireless cooker (page 214) may be used for keeping foods cool as well as hot, since proper insulation will keep the heat out as well as in.

Thermos Bottle

A thermos bottle is a convenient way of keeping a small amount of food cold. A wide-mouthed bottle can be used for other foods than liquids.