PARIS — “Histoire du No.5 Chanel, Un Numéro Intemporel” (or “Story of Chanel No.5, A Timeless Number,” in English) is a book billed to be an “authorized biography” on the mythic scent introduced in 1921. Written by François Ternon and published in French by Editions Normant, it will be released in France, Belgium and Switzerland on Oct. 20. The subjects covered in the 186-paged book include how the fragrance got its name and the manner in which its bottle was chosen. Ternon also retraces important moments in the lives of Gabrielle Bonheur “Coco” Chanel and Ernest Beaux, No.5’s two creators. For the book, Ternon consulted numerous sources, including those from the Société Française des Parfumeurs and the house of Chanel, which also supplied 32 illustrated pages.