The importation of sheep's wool from several different countries, of cotton wool from all countries, of undressed flax, of the greater part of dyeing drugs, of the greater part of undressed hides from Ireland, or the British colonies, of seal skins from the British Greenland fishery, of pig and bar iron from the British colonies, as well as of several other materials of manufacture, has been encouraged by an exemption from all duties, if properly entered at the custom house.