72 Pa. Stat. § 3649
It shall be the duty of the commissioners of the sinking fund, on the first business day of the months of March, April, May, September, October and November respectively, when the certificate named in the preceding section of this act shall be furnished to them, forthwith to use the money shown to be due to them thereby, in purchasing the interest bearing indebtedness of the state, at current market rates, provided the same does not exceed three per cent. above par, and they shall immediately cancel the said indebtedness, and charge the same to the sinking fund in the sinking fund ledger aforesaid, and file the cancelled evidences of indebtedness as vouchers for such payment; it shall also be the duty of the commissioners of the sinking fund, upon the delivery to them of the certificate named in the preceding section of this act, on the first business day of the months of January, February, June, July, August and December, to immediately deposit at the Farmers' and Mechanics' National Bank, in Philadelphia, to the credit of the state, the whole of the moneys shown by said certificates, respectively, to be due to the sinking fund, or such part thereof as in their opinion will be sufficient, with accruing balances, to pay the semiannual interest then next maturing upon the debt of the state; and all of the moneys remaining thereof, after making such deposits, if any, shall be by them forthwith applied to the purchase of the interest bearing debt of the commonwealth, in the manner hereinbefore specified, and the evidences thereof shall in like manner be cancelled, charged to the state sinking fund, and the vouchers duly filed as aforesaid.
72 P.S. § 3649