228 



SCIENCE 



[N. 8. Vol. LII. No. 1340 



and zinc, and partly from a statement of Mois- 

 san^ that it grows in hexagonal plates and 

 rhomhohedra. 



The X-ray analysis shows it to be a perfect 

 face-centered cubic arrangement of atoms, the 

 side of the elementary cube being 5.56 A. 

 Each Ca atom is surrounded by 12 equidistant 

 nearest neighbors, at distances of 3.93 A. 



TITANIUM 



There is no crystallographic data regarding 

 titanium. The X-ray analysis shows it to be 

 a centered cubic arrangement, like chromium 

 and iron. The side of the elementary cube is 

 3.144 A. Each atom is surrounded by eight 

 others, at distances of 2.72 A. 



The arrangement of atoms in zinc is like that 

 in magnesium, namely : hexagonal close packed 

 (one of the two alternative arrangements that 

 solid spheres assume when packed as closely as 

 possible) except that it is elongated 14 per 

 cent, in the direction of the hexagonal axis. 

 The arrangement is that of solid prolate sphe- 

 roids in closest possible packing. 



Each atom is surrounded by six nearest 

 neighbors, in its own plane, at distances of 

 2.67 A, and by six others, three above and three 

 below, at distances of 2.92 A. 



The observed axial ratio, 1.86, bears no 

 simple relation to the value 1.356 found by 

 crystallographers. The data on which the 

 latter is based are, however, very unsatis- 

 factory. 



CADMIUM 



The structure of cadmium is like that of 

 zinc, namely: a close packed arrangement of 

 prolate spheroids. The elongation of the sphe- 

 roids is slightly greater than for zinc, viz., 16 

 per cent., corresponding to an axial ratio (ratio 

 of altitude to side of elementary hexagonal 

 prism) of 1.89. 



Each atom has six nearest neighbors in its 

 own plane at distances of 2.98 A., and six 

 others almost as near, three above and three 

 below, at distances of 3.30 A. 



2 See Groth, Chemische Krystallographie. 



As in the case of zinc the observed axial ra- 

 tio, 1.89, bears no obvious relation to the crys- 

 tallographer's value, 1.335. 



INDIUM 



The atoms of indium are arranged in a 

 face-centered tetragonal lattice. The axial 

 ratio, that is, the ratio of altitude to base of 

 the elementary tetragonal prism, is 1.06. The 

 lattice is therefore like " cubic close packing " 

 except that it is elongated 6 i>er cent, in the 

 direction of one of the cubic axes. It is a close- 

 packed arrangement for prolate spheroids, al- 

 ternative with the zinc and cadmiiun type. 



The side of the elementary prism is 4.58 A., 

 and its height 4.86 A. Each indium atom has 

 four nearest neighbors at distances of 3.24 A., 

 and eight others, four above and four below, at 

 distances of 3.33 A. 



The crystallographic data assigned indium 

 to the cubic system. 



RUTHENIUM 



The arrangement of atoms in ruthenium, 

 like that in zinc and cadmium, is very close to 

 hexagonal close packing. In this case, how- 

 ever, the lattice is shortened in the direction 

 of the hexagonal axis by 3 per cent., giving an 

 axial ratio of 1.59. This is a close-packed ar- 

 rangement for oblate spheroids. 



Each ruthenium atom is surrounded by six, 

 in its own plane, at distance of 2,686A., and 

 by six others, three above and three below, at 

 distances of 2.640 A. 



PALLADIUM 



The atoms of palladium are in face-centered 

 cubic arrangement. This is the " cubic close 

 packed " arrangement for perfect spheres. 



The side of the elementary cube is 3.92 A. 

 Each atom is surrounded by twelve equidistant 

 neighbors at distances of 2.77 A. 



TANTALUM 



The atoms of tantalum are in centered cubic 

 arrangement, like tungsten. The side of the 

 elementary cube is 3.272 A. Each atom is sur- 

 rounded by eight nearest neighbors at dis- 

 tances of 2.83 A. 



