Customs exemption caps acetic acid import duty at a specified ad valorem rate, limiting excess duty on imports. Acetic acid imported under the specified sub heading of Heading No. 29.01/45 is exempt from that portion of customs duty in the First Schedule which exceeds an amount calculated at the rate of 30 per cent ad valorem; the exemption is made under the statutory power in the Customs Act and is effective until 31 March 1986.