Assertion: refining | /r/MadeOf | copper oxide
Facets:
value: in the purification of tin
type: PURPOSE
value: as an impurity
type: MANNER
Source sentences:
text: Poling is a metallurgical method employed in the purification of copper which contains copper oxide as an impurity and also in the purification of tin ("Sn") which contains tin oxide (stannic oxide or "SnO 2 ") as an impurity.