Any committee of either House of Congress before which any private claim against the United States may at any time be pending, being first thereto authorized by the House appointing them, may order testimony to be taken, and books and papers to be examined, and copies thereof proved, before any standing master in chancery within the judicial district where such testimony or evidence is to be taken. Such master in chancery, upon receiving a copy of the order of such committee, signed by its chairman, setting forth the time and place when and where such examination is to be had, the questions to be investigated, and, so far as may be known to the committee, the names of the witnesses to be examined on the part of the United States, and the general nature of the books, papers, and documents to be proved, if known, shall proceed to give to such private parties reasonable notice of the time and place of such examination, unless such notice shall have been or shall be given by such committee or its chairman, or by the attorney or agent of the United States, or waived by such private party. And such master shall issue subpoenas for such witnesses as may have been named in the order of such committee, and such others as the agent or other representative of the United States hereinafter mentioned shall request. And he shall also issue subpoenas at the request of such private party, or parties, for such witnesses within such judicial district as they may desire: Provided, That the United States shall not be liable for the fees of any officer for serving any subpoena for any private party, nor for the fees of any witness on behalf of such party. Said committee may inform the United States attorney for the district where the testimony is to be taken of the time, place, and object of such examination, and request his attendance in behalf of the Government in conducting such examination, in which case it shall be his duty to attend in person, or by an assistant employed by him, to conduct such examination on the part of the United States, or such committee may, at its option, appoint an agent or attorney, or one of its own members, for that purpose, as they may deem best; and in that event, if the committee shall not be unanimous, the minority of the committee may also appoint such agent or attorney or member of such committee to attend and take part in such examination.