Provide that all tenders of cotton and settlements therefor under such contract shall be in accordance with the classification thereof made under the regulations of the Secretary by such officer or officers of the Government as shall be designated for the purpose, and the costs of such classification shall be fixed, assessed, collected, and paid as provided in such regulations and shall be credited to the account referred to in section
55 of this title. The Secretary may provide by regulation conditions under which cotton samples submitted or used in the performance of services authorized by this act shall become the property of the United States and may be sold and the proceeds credited to the foregoing account: Provided, That such cotton samples shall not be subject to the provisions of chapters 1 to 11 of title
40 and division C (except sections
3302,
3307
(e),
3501
(b),
3509,
3906,
4710, and
4711) of subtitle I of title
41. The Secretary is authorized to prescribe regulations for carrying out the purposes of this subparagraph and the certificates of the officers of the Government as to the classification of any cotton for the purposes of this subparagraph shall be accepted in the courts of the United States in all suits between the parties to such contract, or their privies, as prima facie evidence of the true classification of the cotton involved.