Section 6. When a notice has been already served under section sixteen of the said Act on a person chargeable w

6. When a notice has been already served under section sixteen of the said Act on a person chargeable with additional duty under the last preceding section, a supplementary notice shall be served upon him; and the provisions as to notices and receipts, contained in the said Act shall, mutatis mutandis, apply respectively to such supplementary notices and to receipts granted for payments in pursuance thereof.