The Long Salt Pour finish to the old magical transposition of a handful of salt from one hand to another (a variation of an older trick using loose tobacco) was devised by Dai Vernon for his 1938 Harlequin Act. He later traded the secret to Roy Benson, who made it a signature closing piece, as did Fred Kaps some years after. For a detailed history of the Salt Trick and Long Salt Pour, see Levent and Karr's Roy Benson by Starlight (2006, p. 163).
Dick Piser was the first to publish a method for the Long Salt Pour using a hollow rubber ball with a slit, and a thread loop, à la a Stillwell Ball. This appeared in Phoenix, No. 291, Oct. 9, 1953, p. 1162, under the title “Supreme Salt”.