This letterbook covers the period April-September 1906. Most of the correspondence is by Edison and John F. Randolph. There are also a few letters by Mina Miller Edison. Many of the items relate to Edison's search for ores of cobalt and other metals. Included is a letter mentioning his intent to abandon his cobalt search in Canada and to construct mills to extract cobalt from the manganese beds of the southern United States. Also included are letters pertaining to Edison's automobile trip to the manganese belt in North Carolina and adjacent states in May and June. In addition, there are items relating to the business of the Edison Portland Cement Co.; to Edison's plans to construct concrete houses; and to his stock holdings in the Edison Ore Milling Syndicate, Ltd., and the Dunderland Iron Ore Co., Ltd. There are several letters to Josiah C. Reiff discussing Edison's work on quadruplex telegraphy during the 1870s and Reiff's protracted litigation over related matters. Also included are letters regarding the accidental death of Edison's associate A. Theo E. Wangemann. Some of the letters refer to supplies of chemicals and equipment for the West Orange laboratory. Among the items pertaining to family and personal matters are letters concerning Edison's diet; the purchase of property in Fort Myers, Florida, and Milan, Ohio; and the upkeep of Edison's homes in Llewellyn Park and Fort Myers. Also included is a letter to the Bank of Metropolis in which Edison declares his net worth to be "over a million dollars."

The label on the front cover contains the following notation: "Thos. A. Edison. - Personal. - Letter Book from April 1 - 1906 to October 1 - 1906." There is an inscription on the spine with similar information. The spine is also stamped "5." The book contains 498 numbered pages and an index. Approximately 10 percent of the book has been selected.