Absolute X-Ray Wave-Length Measurements

Wave-length of the Kα₁ lines of Cu, Fe, and Mo as determined by a speculum metal grating.---By means of a speculum metal grating, 50 lines to the mm, ruled over a length of 5 mm, the wave-lengths of the Kα₁ line of copper, iron and molybdenum were determined as 1.5373±{}0.0008, 1.937(6)±{}0.002(3) and 0.708(3)±{}0.001(1) angstroms respectively. Using the Kα₁ line of copper the following constants were calculated: the grating space of calcite 3.0290±{}0.0016A, Avogadro's number (6.061±{}0.009) ×{} 10²³ molecules per gram molecule, and the electronic charge (4.774±{}0.007)×{}10^-10 e.s.u. A discussion is given of the sources of error involved, of which the most important are those due to the settings on the lines of the diffraction pattern and those due to the inexact setting of the grating.