sand bath

from The Century Dictionary.

• noun A vessel containing warm or hot sand, used as an equable heater for retorts, etc., in various chemical processes.
• noun In medicine, a form of bath in which the body is covered with warm sea-sand.
• noun The rolling of fowls in sand, by which they dust themselves over to cleanse the skin and feathers; the act of pulverizing; saburration.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A piece of laboratory equipment consisting of a container fitted with heated sand, that is used to provide an even source of heat