after robert collier's death in 1918, p.f. collier & son company was bought by crowell publishing company (later the crowell-collier publishing company). in 1950 collier books published the 20-volume "collier's encyclopedia" (full title "collier's encyclopedia with bibliography and index"). it was expanded to 24 volumes in 1962. until its print edition ceased in 1998, "collier's encyclopedia" was sold almost exclusively door-to-door, one of the last big-ticket items of that nature in the united states.in fact in the 1930-50s one of the qualifiers for the door to door salesman to determine if one could afford the books, was if there was a telephone present in the household..to make 24 volumes more affordable, they were purchased one or two volumes each month over one or two years. for many families they became a status symbol.