user: Question: what is the rank when assumed office on 12 May 1857?
Columns: ['Rank:', 'Premier:', 'Party:', 'Assumed Office:', 'Left Office:', 'TOTAL Time in Office:']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Sir Robert Cosgrove', 'Labor', '18 December 1939', '18 December 1947', '18 years, 182 days']
SQL:

assistant: SELECT "Rank:" FROM "Table" WHERE "Assumed Office:" = '12 May 1857';