From Safer nicotine wiki
- volume: For one publication published in several volumes. Displays after the title and series fields; volume numbers should be entered just as a numeral (e.g. 37). Volume values that are wholly digits, wholly uppercase Roman numerals, or fewer than five characters will appear in bold. Any alphanumeric value of five or more characters will not appear in bold. In rare cases, publications carry both, an ongoing volume and a year-related value; if so, provide them both, for example |volume=IV / #10.