Howard University.

The property, real and personal, of the Howard University shall be exempt from taxation so long as such property shall be used only for the purposes set forth in the charter of said institution; provided, that nothing in this section shall exempt any real estate of said University from assessment and liability for special improvements authorized by law; provided also, that this section shall not include any real estate sold or contracted to be sold by said University to any other person than the United States, the title to which may be still in the said University.