Absolute X-Ray Wave-Length Measurements

Wave-length of the $\mathrm{K}{\alpha }_1$ 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 $K{\alpha }_1$ 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 $K{\alpha }_1$ line of copper the following constants were calculated: the grating space of calcite 3.0290±0.0016A, Avogadro's number (6.061±0.009) × ${10}^{23}$ molecules per gram molecule, and the electronic charge (4.774±0.007)×${10}^{-10\mathrm{}}$ 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.