31 USC 3302 - Custodians of money

(a) Except as provided by another law, an official or agent of the United States Government having custody or possession of public money shall keep the money safe without
(1) lending the money;
(2) using the money;
(3) depositing the money in a bank; and
(4) exchanging the money for other amounts.
(b) Except as provided in section 3718 (b)1 of this title, an official or agent of the Government receiving money for the Government from any source shall deposit the money in the Treasury as soon as practicable without deduction for any charge or claim.
(c) 
(1) A person having custody or possession of public money, including a disbursing official having public money not for current expenditure, shall deposit the money without delay in the Treasury or with a depositary designated by the Secretary of the Treasury under law. Except as provided in paragraph (2), money required to be deposited pursuant to this subsection shall be deposited not later than the third day after the custodian receives the money. The Secretary or a depositary receiving a deposit shall issue duplicate receipts for the money deposited. The original receipt is for the Secretary and the duplicate is for the custodian.
(2) The Secretary of the Treasury may by regulation prescribe that a person having custody or possession of money required by this subsection to be deposited shall deposit such money during a period of time that is greater or lesser than the period of time specified by the second sentence of paragraph (1).
(d) An official or agent not complying with subsection (b) of this section may be removed from office. The official or agent may be required to forfeit to the Government any part of the money held by the official or agent and to which the official or agent may be entitled.
(e) An official or agent of the Government having custody or possession of public money shall keep an accurate entry of each amount of public money received, transferred, and paid.
(f) When authorized by the Secretary, an official or agent of the Government having custody or possession of public money, or performing other fiscal agent services, may be allowed necessary expenses to collect, keep, transfer, and pay out public money and to perform those services. However, money appropriated for those expenses may not be used to employ or pay officers and employees of the Government.
[1] See References in Text note below.