From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison table of material properties for carbon products from makers Le Carbone and Morganite.
| Identifier | WestWitteringFiles\I\July1922\ Scan107 | |
| Date | 24th July 1922 | |
| EPC4/T24.7.22. Maker. | Grade. | Specific Resist: in Ohms per in. cube. | Coefficient of Friction. | Normal Current Density amps. per sq. inch. | Contact Drop in Volts at normal current density. Le Carbone. | Z | .0012 | Not given. | 50 " | EG30 | .0014 | " | 50 Morganite. | EG2 | .0012 | .22 | 60 | .85 " | EG0 | .0016 | .18 | 65 | .85 EPC. | ||