The Chaplin Conway Papers contain fifty-three letters, written by Chaplin to his second wife, Sarah, during his long sea voyages to South America as shipmaster. The only exceptions are the earliest letter of the collection, written to Chaplin from his brother John, expressing sympathy on the death of his first wife (Folder 1), and two letters from Sarah, Chaplin's second wife, to her husband on board ship. The letters are arranged in chronological order. Each letter is folded to be a self-envelope, addressed on the outside, and many are stamped with a postal or shipping rate. Each letter indicates the date and Chaplin's location at the time of writing. Because of the necessity of waiting for a carrier for the letters, many of them are written in the form of journals, and include entries for many days.

The letters provide interesting details of the Salem-Brazil trade, giving the names of ships used in the trade, tracking the trade routes of Chaplin's vessels from one Brazilian port to another in search of favorable trading conditions, and delivering and receiving consignments. There are frequent references to the cargoes carried, both to and from Brazil, with rubber and hides among the important imports into Salem. Only a few comments by Chaplin relate to the political and social events of the time: He hopes "Old Zack" (Taylor) will be elected president. At one point he has taken on a crew member that he believes to be a runaway slave. There are a few brief comments on the population and nature of certain Brazilian ports.