Dense smoke shall mean any smoke so heavy and thick that it substantially obscures any object from plain visibility, or any smoke through which an object can only be seen dimly, or any smoke which is heavy enough to substantially cloud and blanket the surrounding neighborhood atmosphere, or that smoke which has a density of number 2 or greater as established by the Ringelmann's Chart hereinafter referred to and adopted. The Ringelmann's Chart, as used in this section, shall be that standard published by the United States Bureau of Mines to determine the density of smoke as follows:
"The Ringelmann Chart. The standard by which the density of smoke is to be measured will be the Ringelmann Chart, officially published by the United States Bureau of Mines.
"Use of the chart will be made by placing it at such distance from the observer so that the squares appear as even shades of coloring, or when no white spaces between the lines are visible. Comparison of the smoke under observation with the various shades of the chart will then indicate the density of the smoke. Observation distances shall be not less than one hundred (100) feet nor more than one-quarter mile from the smoke observed."
(1953 Code, ch. 18, § 37a)