Interest on delayed tax refunds accrues after statutory period, with higher rate for refunds following final adjudication. Interest is payable where a refund ordered under section 54 is not paid within sixty days of receipt of the application: generally at a rate not exceeding six per cent. from the day after the sixty day period until refund; and, where the claim follows a final order by an adjudicating, appellate or judicial authority, at a higher rate not exceeding nine per cent. for the same period. Appellate or court orders reversing a proper officer are deemed orders under the refund provision.