Section 121. Proposals

No  contract shall be let, except after the receipt
  of sealed bids or proposals therefor, and no bids or proposals shall  be
  received  at any time other than at a regular meeting of said board, and
  unless they conform to the rules of the board and the general ordinances
  of the common council. All bids or proposals must be indorsed  with  the
  title  of  the  work  or materials to which they relate, the name of the
  bidder and his residence. It shall be the duty of  each  member  of  the
  board to be present at the time and place mentioned in the public notice
  for  the  receipt  and  opening  of bids or proposals, and such meetings
  shall be open to the public. After all the bids or proposals  have  been
  presented,  but  not  until  one-half  hour after the time stated in the
  public notice for holding the meeting, all bids or  proposals  shall  be
  opened  by some member of the board or by its secretary, publicly and in
  the presence of the bidders and other  persons  there  present,  and  an
  abstract  of all of such bids or proposals, with the prices and security
  offered, shall be transcribed in a book kept for that  purpose,  without
  any  change,  correction  or  addition whatever. A majority of the board
  need not be present when such bids or proposals are  opened.  The  board
  may  reject  all bids or proposals received at any meeting and advertise
  again for new bids or proposals to be received  at  another  meeting  as
  above  prescribed.  No  person  submitting,  or on whose behalf a bid or
  proposal is submitted, nor the principal or  sureties  on  any  bond  or
  security  accompanying  the  same,  shall  have the right to withdraw or
  cancel any such bid, proposal,  or  bond  until  the  board  shall  have
  awarded  the  contract  for which such bid or proposal is made, and such
  contract shall have been duly executed.