The Department of Administration is hereby directed to require that all state or federal agencies to be housed in the new state office building shall pay rent therefor at a square foot rate to be determined by the Department of Administration, such rent to begin on and continue after July 1, 1965. The revenue derived from the rental paid for space in the said building shall be used by the Department of Administration to apply to the amortization of the cost of the said building, the new office and laboratory building of the Department of Health, and Environmental Control, the purchase of the Standard Oil building on Gervais Street, the equipment for and renovation of the other state office buildings, and for certain other parcels of land previously bought for the account of the state sinking funds in connection with the building program cited above. The total expenditures for which this program is provided shall not exceed the sum of six million five hundred thousand dollars. The amortization of this debt shall be on the basis of three per cent interest for a period of twenty-five years.