Section 236. Prima facie proof

1.  In  any  action  relating  to the
  enforcement of any provision of this article, a certificate duly  issued
  by  an  assay  office  of  the treasury department of the United States,
  certifying the weight of any article, or any part  thereof,  or  of  the
  kind,  weight,  quality, fineness or quantity of any ingredient thereof,
  shall be receivable in evidence as constituting prima facie proof of the
  matter or matters so certified.
    2. In any action relating to the enforcement of any provision of  this
  article,  proof  that  an  article  has  been marked in violation of the
  provisions of this article shall be deemed to be prima facie proof  that
  such article was manufactured after this article became effective.