The lattice constant a has been determined within 0.1 percent (.03 percent for W) for aluminum, iron, nickel, copper, molybdenum, palladium, silver, tungsten, platinum, gold, lead and bismuth, by direct comparison with NaCl, a(NaCl)=2.814A. As pure samples as could be obtained were used, from 99.55 percent for Ni to 99.9995 percent for tungsten, and in many cases commercially pure samples were also measured for comparison. The results for the purest samples are summarized in Table XIII. The density from the x-ray data is in each case (except Al and Ag) greater than the density of the bulk metal as given in the literature, the difference being rather large for Mo (10.21 vs 9.1), for Pd (12.25 vs 11.9) and W (19.32 vs 18.77). For pure W remarkably sharp lines were obtained. For Bi a piece of a single artificial crystal was used.