The low-temperature form of C₁₈H₃₈

The low-temperature form of C₁₈H₃₈, which is iso-structural with that of other even paraffins from C₂₂ down to C₆, is shown to be triclinic, with one molecule in the unit cell, which has dimensions a = 4.28₅ A., b = 4.82₀ A., c = 23.07₀ A., [alpha] = 91° 6', [beta] = 92° 4', [gamma] = 107° 18'. Measurements were made of 118 spacings and 65 angles, by means of Laue, powder, rotation and Weissenberg photographs. The `X-ray' density is 0.93 g.cm^-3 at 21° C., as compared with the liquid density at the melting-point, 27° C., of 0.777 g.cm^-3.