I think the only time you have to use quotation marks is when you want your ref name to have a space in it, as you would between two words, such as <ref name="1850 Census">. To close would be <ref name="1850 Census" />. But instead you can always run your words together, as in <ref name=1850Cen>, and <ref name=1850Cen />.
Spacing is critical, especially no space after the =, and yes before />.