Definition of "crucible"

crucible

/ˈkɹuː.sɪ.bəl/

noun
plural crucibles
1. (chemistry) A cup-shaped piece of laboratory equipment used to contain chemical compounds when heating them to very high temperatures.
  Quotations
  In one corner of the closet was a very small furnace, with a glowing fire in it, and on the fire a kind of duplicate crucible—two crucibles connected by a tube. One of these crucibles was nearly full of lead in a state of fusion, but not reaching up to the aperture of the tube, which was close to the brim.
  1850, Edgar Allan Poe, “Von Kempelen and His Discovery”, in The Works of the Late Edgar Allan Poe
2. A heat-resistant container in which metals are melted, usually at temperatures above 500°C, commonly made of graphite with clay as a binder.
3. The bottom and hottest part of a blast furnace; the hearth.
4. (figuratively) A very difficult and trying experience, that acts as a refining or hardening process.
  Quotations
  But, in considering an author and his works as one, a sufficient distinction is not drawn between the ideal and the real: the last is only given by being past through the crucible of the first.
  1837, L[etitia] E[lizabeth] L[andon], “A First Night”, in Ethel Churchill: Or, The Two Brides. […], volume II, London: Henry Colburn, […], page 70
  We should give our support to the liberation of the captive nations of the world and deliver our compatriots from their crucible of suffering. In other words, we should take up the difficult task of reshaping the world’s destiny by destroying the tyrannical Communist rule now afflicting the earth and by delivering humankind from the Red holocaust.
  1973 July 22 , Kai-shek Chiang, “President Chiang Kai-shek's message to the mass rally supporting Captive Nations Week”, in Free China Weekly‎, volume XIV, number 28, Taipei, page 1
  Some of our ancestors faced trials that we will never know—the snows of Valley Forge; the crucible of a bitter, bloody civil war; and the incredible hardships endured in taming a savage wilderness.
  1982 July 3, Ronald Reagan, Presidential Radio Address‎