In the performance of their duties, the Commissioner of Agriculture or any of his duly authorized agents shall have free access at all reasonable hours to any store, warehouse, factory, storage house, or railway depot where petroleum products are kept or otherwise stored, for the purpose of examination or inspection and drawing samples. If such access shall be refused by the owner of such premises or his agent or other persons occupying and using the same, the Commissioner of Agriculture or his duly authorized inspectors or agents may apply for a search warrant, which shall be obtained in the same manner as provided for obtaining search warrants in other cases. Their refusal to admit an inspector to any of the above-mentioned premises during reasonable hours shall be construed as prima-facie evidence of a violation of this part.