The major experimental problems involved in this investigation were two in number. The first problem was that of obtaining an accurate calibration of the electron microscope to be used for making electron micrographs. This was done by comparison with a secondary standard. A Bausch and Lomb Type ILS metalloscope, which was calibrated by use of a steel grating furnished by the manufacturer, was used as the secondary standard. The second problem was the examination of yellow iron oxide pigments manufactured by three major manufacturers for the purpose of comparing individual pigment particles and also determining particle shape and dimensions. Both problems were successfully solved and the following observations were made: 1. The magnification of the RCA Type ENC electron microscope used in the investigation is 4274. 2. The particle size and structure of yellow iron oxide paint pigments made by different manufacturers are the same, i.e., 0.5 micron by 0.1 micron and rod-like in structure. / Master of Science