150 CARNEGIE INSTITUTION OF WASHINGTON. 



The following papers were published by Dr. R. W. G. Wyckoff, of this 

 Laboratory, while a guest of the Gates Chemical Laboratory of the California 

 Institute of Technology: 



The crystal structure of the hexammoniates of the nickel hahdes. Ralph W. G. Wyckoff. 

 J. Am. Chem. Soc, 44, 1239-1245. 1922. (Contribution from the Gates 

 Chemical Laboratory of the California Institute of Technology, No. 12.) 



It has been shown that in the arrangement of their atoms the hexammoni- 

 ates of nickel chloride, bromide, and iodide are strictly isomorphous with 

 ammonium chloroplatinate. The dimensions of the unit cells for each of 

 these salts and the values of the variable parameters defining the positions 

 of the nitrogen atoms in the chloride and iodide have been estimated. 



The composition and crystal structure of nickel nitrate hexammoniate. Ralph W. G. 

 Wyckoff. J. Am. Chem. Soc, 44, 1260-1266. 1922. (Contribution from the 

 Gates Chemical Laboratory of California Institute of Technology, No. 14.) 



From X-ray spectrum measurements and space-group reasoning it can be 

 shown that the crystals formed on the addition of ammonia to a solution of 

 nickel nitrate can not have the composition usually ascribed to them. Care- 

 ful chemical analysis proves them to be Ni(N03)2.6NH3. A study of the 

 Laue photographs of these crystals by the generally applicable methods 

 which use the theory of space-groups indicates that they have a structure 

 similar to that of the previously studied nickel hexammoniate halides with 

 NO3 groups replacing the halogen atoms and the ammonia groups related to 

 the nickel atoms in the same manner in both compounds. The positions of 

 the atoms of the nitrate groups can not, however, be determined with great 

 accuracy. Both the symmetry characteristics and the diffi-action data permit 

 the same kind of displacement of the nitrate-nitrogen atoms as is experienced 

 by the sulphur atoms in pyrite. 



The symmetry and crystal structure of zinc bromate hexahydrate, Zn(Br03)".6H20. 

 Ralph W. G. Wyckoff. Am. J. Sci., 4, 188-192. 1922. (Contribution from 

 Gates Chfemical Laboratory of California Institute of Technology, No. 16.) 



From a study of the Laue photographs to which crystals of zinc bromate 

 hexahydrate give rise, it is shown that they must have the symmetry of the 

 space-group Th®. Though it is impossible to determine the positions of the 

 atoms in this crystal, such knowledge of the underlying space-group defines 

 uniquely the manner of arrangement of its atoms. The length of the side of 

 the unit cube, which contains 4 chemical molecules, is found to be 10.31 a. u. 



On the symmetry and crystal structure of sodium hydrogen acetate, NaH(C9H302)2. 

 Ralph W. G. Wyckoff. Am. J. Sci., 4, 193-198. 1922. (Contribution from 

 Gates Chemical Laboratory of California Institute of Technology, No. 17.) 



It is shown that the unit cell of sodium hydrogen acetate must contain 24 

 chemical molecules. The length of the side of this unit cube is found to be 

 15.98 A. u. The determination of the underlying space-group as probably 

 Th^ defines the general manner of the arrangement of the atoms of this 

 crystal, though it is impossible to obtain the positions of these atoms. A 

 graphical method is outlined for identifying the planes causing the secondary 

 spectra upon a reflection spectrum photograph. 



The crystal structure of silver molybdate. Ralph W. G. Wyckoff. J. Am. Chem. Soc, 44, 

 1994-1998. 1922. (Contribution from the Gates Chemical Laboratory of the 

 Cahfornia Institute of Technology, No. 18.) 



Using the generally applicable methods based upon the results of the theory 

 of space-groups and taking the data from reflection spectra and Laue photo- 

 graphs, it is shown that silver molybdate has the same crj^stal structure as 

 the spinels and magnetite. The length of the side of the unit cube, which 

 contains 8 molecules, is 9.26 a. u.; the parameter defining the position of 

 the oxygen atoms is close to 3/8. 



