user: Question: Name the date successor seated for successor being Vacant
Columns: ['District', 'Vacator', 'Reason for change', 'Successor', 'Date successor seated']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Colorado Territory At-large', 'New seat', 'New seat', 'Hiram P. Bennett (Conservative R)', 'August 19, 1861']
SQL:

assistant: SELECT "Date successor seated" FROM "Table" WHERE "Successor" = 'Vacant';