Section 13. When any such officer has, in exercise of the powers conferred by section 12, or by purchase, obtain

13. When any such officer has, in exercise of the powers conferred by section 12, or by purchase, obtained a sample of petroleum in the possession of a dealer, he may give a notice in writing to the dealer informing him that he is about to test the sample, or cause it to be tested, at a time and place to be fixed in the notice, and that the dealer or his agent may be present at the testing. Possession and transport of petroleum. Power to inspect and require dealer to sell samples. Notice to be given when officer proposes to test samples.