Вештачка гума — разлика између измена

* {{Cite book |ref= harv|last=Slack|first=Charles|title=Noble Obsession: Charles Goodyear, Thomas Hancock, and the Race to Unlock the Greatest Industrial Secret of the 19th Century|url=http://books.google.com/books?id=XuUjgUaZzOAC|year=2003|publisher=Hyperion Books|isbn=978-0-7868-8856-6}}

* -{Neal Ascherson, ''The King Incorporated'', Allen & Unwin, 1963. ISBN 978-1-86207-290-9 (''1999 Granta edition'').}-

* -{Petringa, Maria: ''Brazza, A Life for Africa''. Bloomington, IN: AuthorHouse. {{page|2006|978-1-4259-1198-0|pages=}}}-