nov. 4, 1923 WYCKOFF AND POSNJAK: CRYSTAL STRUCTURES 395 
assigned structure (Table II). The calculated intensities were ob- 
tained with the expression ® 
d 2.35 , 
r= (2) xs x 4(R + X) 
This formula, involving as it does the rule of ‘‘normal decline” and a 
proportionality between the number of electrons in atoms and their 
TABLE I.—PowpErR Puotrocrapuic Data upon LirHium IopDIDE 
INTENSITY 
INDICES SPACING ay ere ee ge ee REMARKS 
Observed Calculated 
(hkl) A A 
eee 4.50 So 5 ae Hydrate line 
Gwen) 3.50 6.06 10— 95, 000 units 
100(2) 3.06 [6.12] 10 59, 000 Hydrate line also 
tone 2.47 Lok. 1 how dié Hydrate line 
110(2) 2.14 6.06 6 52, 000 
113(1) 1.80 5.99 6 61, 700 
100 (4) 1.52 [6.08] 1 11, 600 
133 (1) 1.37 6.00 3 31, 800 
112(2) | 12238 6.04 2 28, 800 
6.03A average 
TABLE II.—Intensiry Data vreon Lituium IoDIDE 
6 ee ee ee ee ee EEE ee 
INTENSITY 
INDICES 
Observed Calculated 
111(1) 3 24 
100 (2) 15 15 
110(2) 10 13.3 
311(1) 2 15.8 
111(2) 3 5.3 
100(4) 1.5 2.9 
133(1) 1 8.1 
eee ee ee. ee SS ee 
scattering powers,’ cannot possibly give quantitatively accurate 
results, but experience with different crystal structures, the rest of 
the alkali halides for instance, indicates that they are qualitatively 
correct. 
From these different lines of evidence it seems necessary to con- 
clude that the substance used in the second determination? of the 
8R. W. G. Wycxorr and E. W. Posngax, Journ. Am. Chem. Soc. 44: 30. 1922. 
R. W. G. Wycxkorr, op. cit. 
9 W.H. and W. L. Braae, X-rays and crystal structure, London, 1918. 
