"United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M9SL-7RD : accessed 28 September 2019), Bulha Haltwig in household of Julius Haltwig, Plymouth Township, Hennepin, Minnesota, United States; citing enumeration district (ED) 149, sheet 5B, family 97, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,240,770.
"Arizona Deaths, 1870-1951," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:FLV6-6HR : 16 May 2019), Bertha Zellmer in entry for Paul August Hartwig, 25 Jun 1944; citing Phoenix, Maricopa, Arizona, reference 282, Department of Library and Archives, Phoenix, Arizona; FHL microfilm 2,135,637.
Ancestry.com. U.S., Social Security Applications and Claims Index, 1936-2007 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2015.
Find A Grave, database and images (https://www.findagrave.com : accessed 28 September 2019), memorial page for Bertha Hartwig (20 Oct 1850–23 Jun 1904), Find A Grave: Memorial #15682865, citing Mount Olivet Chapel Cemetery, Plymouth, Hennepin County, Minnesota, USA ; Maintained by Find A Grave (contributor 8) .
Staatsarchiv Hamburg. Hamburg Passenger Lists, 1850-1934 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2008. Staatsarchiv Hamburg; Hamburg, Deutschland; Hamburger Passagierlisten; Volume: 373-7 I, VIII A 1 Band 070; Page: 207; Microfilm No.: K_1743
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