JOURNAL 
OF THE 
WASHINGTON ACADEMY OF SCIENCES 
Vou. 13 NOovEMBER 4, 1923 No. 18 
CRYSTALLOGRAPHY .—A note on the crystal structures of lithium 
todide and rubidium fluoride. Ratepo W. G. WycKkorr and 
Kucen W. Posnsgax, Geophysical Laboratory. 
A study of the crystal structures of all of the alkali halides, except 
rubidium fluoride, has been published;! further powder data upon all 
of them have also been given recently.2. The results of the study 
of lithium iodide in these two investigations, however, are conflict- 
ing, and the published data upon rubidium fluoride are not in accord 
with the writers’ preliminary observations. The present paper is 
devoted to a discussion of these discrepancies. 
The structure of lithium todide. As ordinarily prepared, lithium 
iodide crystallizes as a hydrate. The trihydrate, stable up to + 75°C., 
yields on heating a di- and finally a mono-hydrate. Theanhydrous 
salt, which is excessively hygroscopic, is obtained only by holding 
the monohydrate? at temperatures above 300°C. The specimen 
used in the first determination! was prepared by melting anhydrous 
lithium iodide, grinding the solidified salt while still hot in an oven, 
and immediately introducing it into a glass specimen tube which 
was then sealed. Even under these conditions the resulting powder 
photographs showed that probably not less than 20 per cent of the 
sample had hydrated. The crystalline powder used in the other 
study? of lithium iodide was obtained by evaporating a solution of 
lithium iodide over sulfuric acid. It is known that the trihydrate 
is produced! at 0°C. by this procedure, and both the known properties 
1R. W. G. Wycxorr, Journ. Washington Acad. Sci. 11:429. 1921. E. W. Posnyax 
and R. W. G. Wycxorr, ibid. 12: 248. 1922. 
2W. P. Davey, Phys. Rev. 21: 143. 1923. 
5, AUERBACH and J. F. Bristex in Abegg’s Handbuch der anorganischen Chemie 2, 
Abt. 1:°130. 
4 GMELIN-KRAUT-FRIEDHEIM, Handbuch der anorganischen Chemie 2, Abt. 1: 258. 
393 
