Begin with the title of the article. Place the title in quotes and follow it with a period. Use the first main word in the title to place it alphabetically in your list of works cited. If the title is "Igneous Rocks," your citation should begin like this:"Igneous Rocks."
Follow the title of the article with the title of the reference book. The title should be italicized or underlined, but if your word processor will not support this type of formatting, use an underscore symbol to indicate that the title should be underlined. For example, if you read the article in "The Encyclopedia Britannica," your citation should thus far look like this:"Igneous Rocks." _Encyclopedia Brittanica_.
Add the edition of the reference book.This information is usually listed right after the title, but it can also be found on the inside cover or on the title page. You can use numerals to indicate the edition number and abbreviate "edition" as "ed." For example, if you are using the 23rd edition of a reference book, your citation should now read:"Igneous Rocks." _Encyclopedia Brittanica_. 23rd ed.
Finish with the year of publication and a final period. This information is also generally available on the inside cover or title page. If the reference book was published in 1999, your finished citation should read:"Igneous Rocks." _Encyclopedia Brittanica_. 23rd ed. 1999.