Ringelmann smoke chart  
U.S. Bureau of mines. 
 - IC 8333 
 - Washington  Bureau of mines  1967 
<br/><br/><label>Subjects--Topical Terms: </label><br/>CUADRO<br/>MINERALOGIA<br/>MINERIA<br/>HUMO
<br/><br/><label>Universal Decimal Class. No.: </label>622 : 549 (797) (047)