As a youth, Deats started collecting postage stamps of the United States and the Confederate States of America and eventually created one of the finest collections of his era, eventually selling the collection.
Deats specialized in the collecting of United States revenue stamps, and his collection, which in 1888 included the revenue collection of Edward Sterling, was unsurpassed. George L. Toppan and Alexander Holland used this collection as a basis for writing, in 1899, An Historical Reference List of the Revenue Stamps of the United States Including the Private Die Proprietary Stamps, which was re-printed in 1979 as The Boston Revenue Book.
Deats also formed one of the finest libraries of philatelic books and literature in the United States, which, in 1952, he donated to the Free Library of Philadelphia.