Section 11. When any such officer has, in exercise of the powers conferred by section ten, or by purchase, obtai

11. When any such officer has, in exercise of the powers conferred by section ten, or by purchase, obtained a sample of petroleum in the possession of a dealer, he may give a notice in writing to such dealer informing him that he is about to test such sample or cause the same to be tested with the apparatus and in the manner described in the schedule hereto annexed, at a time and place to be fixed in such notice, and that such person or his agent may be present at such testing. Certificate as to result of such testing.