7. The Collector may also, by a special notice, require any such person to attend before or before any person authorized by the Collector in that behalf, within a specified time, which shall not be less than fifteen days after the service of the notice, at any places, for any of the purposes aforesaid; any every person on whom such special notice may be served shall be legally bound to attend as required by the notice, and to do any of the things mentioned in section 5, and to give any information which may be required, so far as he may be able to give it.