It is generally more useful to create a separate entry for each volume. In the following example, the writer has cited a passage from the second volume of a novel scanned and archived on the Web site Internet Archive. Since each volume has a separate URL, a works-cited-list entry has been created for each volume. Following the MLA template of core elements, each entry provides the novel’s volume number and publication information in the first container. The second container lists the name of the Web site and the URL for the volume. The parenthetical citation indicates the volume and page number for the citation:
The narrator of George MacDonald’s David Elginbrod notes that “David was not given to boasting” (2: 160).
MacDonald, George. David Elginbrod. Vol. 1, Hurst and Blackett, 1863. Internet Archive, archive.org/details/davidelginbrod02macdgoog.
---. David Elginbrod. Vol. 2, Hurst and Blackett, 1863. Internet Archive, archive.org/details/davidelginbrod03macdgoog.
---. David Elginbrod. Vol. 3, Hurst and Blackett, 1863. Internet Archive, archive.org/details/davidelginbrod01macdgoog.
You could also site the work as a whole and truncate the URL to the host name (e.g., archive.org). Read more about truncating URLs.