law: Transfer of Property Act, 1882
  82. Contribution to mortgage-debt
  Where property subject to a mortgage belongs to two or more
  
  persons having distinct and separate rights of ownership therein, the different
  
  shares in or parts of such property owned by such persons are, in the absence
  
  of a contract to the contrary, liable to contribute rateably to the debt
  
  secured by the mortgage, and, for the purpose of determining the rate at which
  
  each such share or part shall contribute, the value thereof shall be deemed to
  
  be its value at the date of the mortgage after deduction of the amount of any
  
  other mortgage or charge to which it may have been subject on that date.
  Where, of two properties belonging to the same owner, one is
  
  mortgaged to secure one debt and then both are mortgaged to secure another
  
  debt, and the former debt is paid out of the former property, each property is,
  
  in the absence of a contract to the contrary, liable to contribute rateably to
  
  the latter debt after deducting the amount of former debt from the value of the
  
  property out of which it has been paid.
  Nothing in this section applies to a property liable under section
  
  81 to the claim of the subsequent mortgage.