Section 157. Release of part of mortgaged premises

If  the owner of
  mortgaged premises sell a part thereof, the comptroller, on  application
  and with the consent of the mortgagor or such owner may release the part
  of  the  mortgaged  premises  sold  from  the lien of the mortgage. Such
  release, however, shall not be  given  unless  a  sum  approved  by  the
  comptroller shall be first paid upon the mortgage and unless the part of
  the  mortgaged  premises  remaining  unsold,  exclusive of buildings and
  prior liens, is worth double the  residue  of  the  mortgage  debt.  The
  comptroller  shall  execute  such release in the usual form, which, when
  acknowledged, shall be recorded by the county clerk and a minute thereof
  made upon a margin of the mortgage.