Links
- Immigrant Entrepreneurship: German-American Business Biographies - Hackfeld, Heinrich (1816-1887)
- Article by Peter Young on H Hackfeld
- https://plus.google.com/+PeterTYoung/posts/Nbwzrk5jTB2
- http://files.usgwarchives.net/hi/statewide/bios/isenberg34bs.txt
- https://www.revolvy.com/main/index.php?s=Amfac%20(Hawaii)&item_type=topic