If your source is part of a numbered sequence, provide the type of number followed by the number (e.g. vol. 2). Common numbered sequences are volume (vol.), issue (no.), season, episode.
Abbreviate volume to vol. and number to no.
This element ends with a comma.
Rabb, Nathaniel, et. al. "Truths About Beauty and Goodness: Disgust Affects
Moral but not Aesthetic Judgments." Psychology of Aesthetics, Creativity
and the Arts, vol. 10, no. 4, 2016, pp. 492-500. PsycINFO,
doi:10.1037/aca0000051. Accessed 12 Nov. 2016.
Some texts are issued in multi-volume sets. If you consult one volume of a numbered multi-volume set, indicate the volume number.
Rampersad, Arnold. The Life of Langston Hughes. 2nd ed., vol. 2, Oxford UP, 2002.
Wellek, Rene. A History of Modern Criticism, 1750-1950. Vol. 5, Yale UP, 1986.
In the first example, the vol. is not capitalized because it continues from the version core element (2nd. ed.) which ends in a comma.
For more information, refer to pages 39-40 of the MLA Handbook, 8th ed.