National Geographic : 1939 Nov
626 THE NATIONAL GEOGRAPHIC MAGAZINE Photograph by J. Baylor Roberts BELCHING POISON AGAINST TOBACCO WORMS AT ONE ACRE A MINUTE The plane flies low and operates only in early morning, when the air is still and the crops wet with dew. Poison itself is carried in dust made of lime, talc, or bentonite clay (page 628). moLHiH^H Photograph by Akron Studios GLOVED AND GOGGLED, AMID HEAT AND STENCH HE TESTS HIS ACID These jumbo vats are sulphuric-acid coolers in the chamber acid plant of the du Pont Com pany's Grasselli Chemicals Department, at Philadelphia. By odd coincidence, the first United States patent ever granted went to a Philadelphian for a sulphuric-acid process (page 632).