Use the Number element when the source you are citing is part of a sequence, liked a numbered volume, issue, episode or season. Examples of when you will use the number element:
Abbreviate vol._, no._, (insert correct number in blank spaces!). Only include the number, not any other information about the volume.
Examples:
Emberling, Geoff, and Helen McDonald. "Recent Finds from the Northern Mesopotamian City Tell Brak." Antiquity, vol. 76, no. 294, 2002, p. 949. World History in Context, link.galegroup.com/apps/doc/A95914911/WHIC?u=new11256&xid=635aebee.
Maspero, Gaston, and Archibald Henry Sayce. “The Gods of Egypt.” History of Egypt, Chaldaea, Syria, Babylonia, and Assyria. e-Book. Vol. 1, Grolier, pp.105-106, 1903. Gutenberg, 21 Feb. 2006, archive.org/stream/egypt01maspuoft?ui=embed.