72 Pa. Stat. § 3732
The said fund, and all interest, increment, and additions thereto, shall be and remain in the custody of the State Treasurer, and shall be invested and reinvested by him, under the supervision and direction of the Board of Finance and Revenue, in lawfully issued interest-bearing securities of the United States of America, the Commonwealth of Pennsylvania, or any other of the United States, or any county, city, borough, or school district of this Commonwealth, or any obligations of municipalities of other States, but, preferably, in such securities issued by municipalities within this Commonwealth: Provided, however, That current receipts and income applicable to said fund shall be deposited, at interest, in the legal depositories of the public funds, until the same shall accumulate in sufficient amount to justify the investment thereof in interest-bearing securities, as hereinbefore provided.
72 P.S. § 3732