CRYSTALLOGRAPHICAL RELATIONSHIP 269 



(b) Interfacial Angles 



For the alkalies the order is : Rb, NH 4 , Cs, with NH 4 very near 

 Rb. The interval Cl Br is of the same order of magnitude as the 

 interval Rb Cs. The greatest change in interfacial angles is obtained 

 by replacement within the group Fe, In, Tl; the effect is roughly 

 proportional to the change in atomic weight. The effect of the 

 replacement In>Tl is opposite in sense to that of NH 4 >Cs, Cl>Br, 

 Fe>In, orRb>NH 4 . 



(c) Molecular Volumes, Axial Constants, and Molecular Distance 



Ratios 



In regard to molecular volume and molecular distance ratios, the 

 alkalies stand in the following order: K, NH 4 , Rb, Cs, with NH 4 

 near to Rb. Replacement affects mainly the \ an d >/ values. Substi- 

 tution of Br for Cl causes an especially large extension along the three 

 axial directions, a fact which probably indicates a symmetrical disposi- 

 tion of the halogen atoms in the molecule. Within the group Fe, In, 

 Tl, replacement has only a small effect on the molecular volume and 

 molecular distance ratios, the effect being seen mainly in the co value. 

 In and Tl are more closely related than are Fe and In. 



The axial constants afford no definite results in this connection. 

 5. In the complex salts of indium and thallium under consideration, the 

 greater the atomic weight of the alkali, the less is the amount of 

 water in the salt. The greater the atomic weight of the alkali, the less 

 also is the ratio RX : MX, in the chemical constitution of the salt. 

 The ratio RX : MX S is, speaking generally, lower in the indium chlorides 

 than in the corresponding thallium chlorides, and in the thallium 

 bromides than in the corresponding indium bromides. The relative 

 concentrations of complex ions in the thallium and indium solutions are 

 important factors in determining the stability of the various salts. 



I have to acknowledge my deep indebtedness to Professor Hugh Marshall, 

 of University College, Dundee, in whose laboratory the experimental part of 

 this investigation was carried out, for his valuable advice and for his great 

 interest in the work. 



BIBLIOGRAPHY 



1. MARSHALL Proc. Roy. Soe. Edin., 1902, 24, 3. 



MARSHALL and WALLACE Jour. Chem. Soc. (not yet published). 



2. THIEL and KOELSCH Zeitschr. f. anorg. Chem., 66, 280. 



3. THIEL Zeitschr. f. anorg. Chem., 1904, 40, 280. 



