Section 33. And be it further enacted by the authority aforesaid, That it shall be the duty of the said board of health, and they are hereby authorised, to invest all sums of money which may at any time be in the hands of their treasurer, over and above the amount which may be necessary to meet their current expenses in the funded debt of the United States, the stock of the bank of the United States, or in the stock of any other incorporated bank in the city of Philadelphia, and to sell and transfer the same at such times and in such portions as necessity may require.