This notebook was used by Edison, William Walter Dinwiddie, Archie D. Hoffman, and possibly other experimenters during April-June 1917 for notes on efforts to produce a perfect disc record blank. The entries pertain primarily to a sequence of experiments numbered from 1472E through 1567E. Included are tests of experimental lots of record blanks constructed by different methods or prepared with different ingredients, along with \"drop\"" tests intended to determine the durability of disc records by dropping them numerous times on the floor. Between experiments 1495 and 1496 is a summary by Dinwiddie of previous \""Rosin Blank experiments,\"" numbered from 1470 through 1486. Many of the entries are in the form of instructions by Edison or Dinwiddie describing the experimental records wanted, accompanied by evaluations of the test records produced. Flaws and successful results are both noted, along with comments on the durability and thickness of the records. One entry refers to the possible use of nickel plating (later adopted) on the face of the copper record molds. The last entry announces the \""discovery of an important principle,\"" which is pursued in Book No. 22: the powder in the rubber-packing press must be considered as a mixture of powder and air, and the air must somehow be eliminated. Inserted into the book is one note by Edison, as well as some calculations by an unidentified experimenter. The front cover is labeled \""Disc Records\"" and \""21\""; the back cover is labeled \""21.\"" The pages are unnumbered. Approximately 150 pages have been used."