-668§ 3655. Payment of interest on failure to invest A trustee who omits to invest the trust moneys according to section 3654 of this title shall pay simple interest thereon, if the omission is negligent merely, and compound interest if it is willful. § 3656. Purchase by trustee of claims against trust fund A trustee may not enforce a claim against the trust property which he purchases after or in contemplation of his appointment as trustee; but he may be allowed, by a competent court, to charge to the trust property what he has in good faith paid for the claim, upon discharging it. Subchapter III—Powers of Trustees § 3681. Authority as general agent A trustee is a general agent for the trust property. His authority is only such as is conferred upon him by the declaration of trust and by this chapter. His acts, within the scope of his authority, bind the trust property to the same extent as the acts of an agent bind his principal. § 3682. Uniting by cotrustees in acts to bind trust property Where there are several cotrustees, all shall unite in an act to bind the trust property, unless the declaration of trust otherwise provides. § 3683. Discretionary powers A discretionary power conferred upon a trustee is presumed not to be left to his arbitrary discretion, but may be controlled by the proper court if not reasonably exercised, unless an absolute discretion is clearly conferred by the declaration of trust. Subchapter IV—Rights of Trustees § 3701. Indemnification A trustee is entitled to the repayment, out of the trust property, of all expenses actually and properly incurred by him in the performance of his trust. He is entitled to the repayment of even unlawful expenditures, if they were productive of actual benefit to the estate. § 3702. Compensation Except as provided by section 3782 of this title, when a declaration of trust is silent upon the subject of compensation the trustee is entitled to the same compensation as an executor. If it specifies the amount of his compensation, he is entitled only to the amount thus specified. If it directs that he shall be allowed a compensation but does not specify the rate or amount, he is entitled to such compensation as may be reasonable under the circumstances. If there are two or more trustees, the compensation shall be apportioned among the trustees according to the services rendered by them respectively. § 3703. Involuntary trustee An involuntary trustee, who becomes an involuntary trustee through his own fault, has none of the rights mentioned in this subchapter. Subchapter V—Termination of the Trust § 3721. Extinguishment A trust is extinguished by the entire fulfillment of its object, or by the object of the trust becoming impossible or unlawful.