No portion of the property of any of said cities¹ shall be used for purposes of private gain by any official, councilman, agent or employé of said city, or of any department thereof, nor shall the same be wilfully used or injured, or sold or disposed of in any manner, without the consent of councils, by any such official, councilman, agent or employé. Nor shall any official, councilman, agent or employé of said city, or any department thereof, be interested, either directly or indirectly, either personally or as a member or officer of any firm, company or corporation contracting with the said city, or any department thereof, for the use, lease, occupation or enjoyment of any of the works, material or property of said city; and any breach of the provisions of this section shall be a misdemeanor, and upon conviction thereof shall be punished by fine not exceeding one thousand dollars and imprisonment not exceeding one year, or either, at the discretion of the court trying the same; and upon such conviction the party offending shall be forthwith removed from his office or employment, and shall not be eligible to appointment to any place of profit or trust under said city or any department thereof.