If your ancestors were immigrants from the Rhineland and left in the 19th century this is a source you don’t want to miss! The Landesarchiv Rheinland has some information on renunciation of citizenship of emigrants leaving their homeland. You can check this site that lists 63347(!) names of emigrants. Go to this link, scroll down and then click on “Zum Findbuch 211.22.01” to get to the spread sheet.