The crystalline structure of naphthalene. A quantitative X-ray investigation

Crystal Data .Naphthalene .—C10 H8 . Melting point 80° C. Density 1·152 (calc. 1·172). Monoclinic prismatic,a = 8·29,b = 5·97,c = 8·68 A., β = 122·7°. Space group C2λ 5 (P21 /a ). Two molecules per unit cell. Molecular symmetry, centre. Molecular volume, 362 A3 . Total number of electrons per unit cell = F(000) = 136.Experimental—Measurements of Intensities . When a small single crystal is placed completely in an X-ray beam, the integrated reflection is proportional to the mass of the crystal, if the latter is sufficiently small. Although fairly large crystals of naphthalene can easily be obtained, the aim in this work has been to carry out the measurements on specimens small enough for this proportionality to hold good. With soft, organic crystals of the hydrocarbon type, the size required for reliable results is found to be of order of 0·1 milligrams.