"I am trying to connect John Christmann from Milwaukee b 1818 back to Lorraine. ..."
There were both family death notices and an obit. for a Johann Christmann (90 yr) in local German newspapers. He was survived by an Albert Christmann. The age would match the birth year you've posted (in genealogy years).
"Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950).
For more specific information contact:
Gary Rebholz, compiler/editor
Indexing Milwaukee's German newspapers continuously since 2007... helping to access our historic immigrant cultures.