Section 23. Powers hereby granted, how to be exercised

1. The powers
  granted by this act are to be exercised  by  the  officer,  officers  or
  official  body  vested with such powers by any other provision of law or
  ordinance (subject to amendment or repeal of any such ordinance) and  in
  the  manner and subject to the conditions prescribed by law or ordinance
  (subject to amendment or repeal of any such ordinance), but no provision
  of any special or local law shall operate to defeat or limit  in  extent
  the  grant  of  powers  contained  in this act; and any provision of any
  special or local law which in any city operates, in terms or in  effect,
  to prevent the exercise or limit the extent of any power granted by this
  article,  shall  be  superseded.  Where any such provision of special or
  local law is superseded under the provisions of this  subdivision,  such
  power,  freed  from  the limitations imposed by such provision, shall be
  exercised by the same officer, officers or official body that  would  be
  vested  with  the same under the provisions of this subdivision, if such
  provision had not been superseded, but the  exercise  thereof  shall  be
  subject  to  the  limitations  provided  for  in subdivision two of this
  section.
    2. In the absence of any provision of law or ordinance determining  by
  whom  or  in what manner or subject to what conditions any power granted
  by this act shall be exercised, the common council or board of  aldermen
  or  corresponding  legislative  body  of  the city shall, subject to the
  provisions of this section, have power by ordinance to determine by whom
  and in what manner and subject to what conditions said  power  shall  be
  exercised.    The  exercise  by  any  city  of any power granted by this
  article not now vested in such city or now vested in such  city  subject
  to  provisions which are superseded by the provisions of subdivision one
  of this section, shall be subject to the following limitations:
    b. No sale or lease of city real estate or of any franchise  belonging
  to  or  under the control of the city shall be made or authorized except
  by vote of three-fourths of all the members of  the  common  council  or
  corresponding  legislative  body of the city. In case of a proposed sale
  or lease of real estate or of a franchise, the  ordinance  must  provide
  for  a  disposition of the same at public auction to the highest bidder,
  under proper regulations as to the giving of security and  after  public
  notice  to  be  published at least once each week for three weeks in the
  official paper or papers. A sale or lease of real estate or a  franchise
  shall  not  be  valid  or  take  effect  unless  made  as  aforesaid and
  subsequently approved by a resolution  of  the  board  of  estimate  and
  apportionment  in any city having such a board, and also approved by the
  mayor. No franchise shall be granted or be operated for a period  longer
  than  fifty  years. The common council or corresponding legislative body
  of the city may, however, grant to the owner or lessees of  an  existing
  franchise,  under  which  operations are being actually carried on, such
  additional rights or extensions in the street or streets  in  which  the
  said  franchise exists, upon such terms as the interests of the city may
  require, with or without any advertisement, as the  common  council  may
  determine,  provided,  however,  that  no  such grant shall be operative
  unless approved by the board of estimate and apportionment in  any  city
  having  such  a  board, and also by the mayor.  In any city the question
  whether any proposed sale or  lease  of  city  real  estate  or  of  any
  franchise  belonging  to  or  under  the  control  of  the city shall be
  approved shall, upon a demand being filed, as hereinafter  provided,  be
  submitted  to  the voters of such city at a general or special election,
  after public notice to be published at least once each  week  for  three
  weeks  in  the official paper or papers. Such demand shall be subscribed
  and acknowledged by voters of the city equal in number to at  least  ten
  per  centum  of  the total number of votes cast in such city at the last

  preceding general election and shall be filed in the office of the clerk
  of such city before the adoption of an ordinance or resolution making or
  authorizing such sale or lease. If such demand is filed,  as  aforesaid,
  such  sale  or  lease  of  real  estate or such franchise shall not take
  effect unless in addition to the foregoing requirements  a  majority  of
  the  electors  voting  thereon  at  such  election  shall  vote  in  the
  affirmative.
    The foregoing limitations shall not apply to the exercise by any  city
  of  any  power  now  vested  in it, where the existing provisions of law
  determining by whom or in what manner or subject to what conditions such
  power shall be  exercised  are  not  superseded  by  the  provisions  of
  subdivision  one  of this section; but in such case the exercise of such
  power shall be subject only to such  existing  provisions  of  law,  and
  shall not be limited or restricted by any provision of this section.