A sinking fund or any part thereof shall be applied in or towards the discharge of the loan or a part of the loan for which such fund was created, and until such loan or part is wholly discharged shall not be applied for any other purpose:
     Provided that when any loan or part thereof has been consolidated under section 193, the Commissioner shall transfer to the sinking fund of the consolidated loan such part of the sinking funds of the original loans as may be proportionate to the amount of the original loans incorporated in the consolidated loan.