Physics. — "Research by means of Rontgen-Eays on the Structure 

 of the Crystals of Lithium and some of its Compounds loith 

 Light Elements. II. Lithium- Hydride \ By J. M. Bijvoet and 

 A. Karssen. (Communicated by Prof. P. Zeeman). 



(Communicated at the meeting of February 25, 1922.) 



1. Introduction. The investigation with X-rajs on the structure 

 of lithium-hydride w&.b taken up in connection with the analogy 

 drawn by Moers^) between lithium hydride and the heteropolar 

 alkali halogenides. 



2. Röntgenograms. The photogiaphs were made as described in 

 our preceding paper *). The difficulty presented itself that after the 

 exposures the hydride-content had been reduced by 15 or 20 percents 

 of weight. The parasitical lines were eliminated : by comparing 

 the photographs of samples of decreasing hydride-content (the place 

 of the LiH-lines appeared to be independent of the degree of decay, 

 hence no formation of mixed crystals) ; by photographing a coarse 

 crystallized, non-rotated sample, appearing the interference lines of 

 LiH markedly distinguished by dots of greater intensity ; by 

 checking up 'the parasitical lines by those of LiOH). 



3. Calculation. The table contains for LiH the values of 10' 



sin* - for the centres of the a-lines. As appears from the occurrence 



of a factor 77,5 =fc 0,5 LiH is regular, and the side of the elementary 

 cell a = 4, 10.10~s cm. B'rom this common factor the number 

 of particles per elementary cell, n is calculated to be 4.30, with the 

 aid of the density according to Moeks, niol. weight, constant of Avogadro, 

 and wavelength Crxa ('esp. 0,816 ; 7.94; 0,6062 . JO'^ and 2,284 .lO-»). 

 This points to n =i 4, which is in agreement with the supposed 

 NaCl structure together with the absence of the planes of mixed indices. 



1) MoERS, Z. f. allg. u. anorg. Ghem. 113, 179. (1920). 



Nernst, Z. f. Elektrochemie 26, 323 and 493 (1920). 

 3) Bijvoet and Karssen. These Proceedings Vol. XXlll, p. 1365. 



