For the purpose of obtaining such loan the Governor may issue certificates of loan or bonds of the Commonwealth. Such certificates or bonds shall bear interest at not more than four per centum per annum, which shall be payable in lawful money of the United States, semiannually, at the office of the State Treasury at Harrisburg, on the first day of February and the first day of August.

The certificates of loan or bonds, issued under the authority of this act, shall be payable at any time after the expiration of ten years, and within twenty-five years from the date of issue. Such bonds or certificates shall not be subject to taxation for any purpose whatsoever.