Rubidium Chloraurates and Bromaurates. 



161 



The axial ratios are as follows : 



CsAuCl 4 

 d:b:c = 1-1255: 1 : 0-7228 

 ,3= 71° 36' 

 RbAuCl 4 

 a:b: c = 1-1954: 1 : 0'7385 

 3 = 75° 32' 



CsAuBr 4 

 d:b:c = 1-1359: 1: 0-7411 



[3 = 70° 24.Y 

 RbAuBr 4 

 ;:b c : = 1-1951: 1: 0-7256 

 (3 = 76° 53£' 



In the following tables the angles which were chosen as 

 fundamental are marked by an asterisk. 



CsAuCl 4 



CsAuBr 4 





Measured. 



Calculated. 



Measured. 



Calculated. 



to a m, 



110^110 = *93° 



46' 







*93° 53' 





m a c, 



HOaOOI = 77 



36 



77° 



32' 



*76 46 





to a d, 



110*021 = 44 



6 



44 



7 



43 23, 



43° 20' 



d * p, 



021*111 = 









32 23 



32 40* 



d a e, 



021^ 201 — " x 75 



17 







75 31 



75 59 



to a e. 



110 a 201 = *60 



36 







*60 41 





c a e. 



001a 201 = 64 



20, 



64 



18 







TO a TO, 



Reentrant angle of twin, 







27 58 



27 58 







RbAuCl 4 





RbAuBr 4 





Measured. 



Calculated. 



Measured. 



Calculated. 



to a m, 



110 a110 = *98° 



21' 







*98° 40' 





TO a C, 



110 a 001 = *80 



36 







*81 30 





TO a d, 



110 a021 = 









44 57 



45 12* 



d* p, 



021 aIII = 









31 26 



31 35* 



d y. e, 



021 a 201 = 







- 



72 28 



72 26 



to a e, 



110 a 201 = *62 



12 







62 9 



62 21* 



c a e, 



001 a 201 = 60 



4 



59° 



59' 







tf .. d 



021 a021 = 110 



20 



110 



4£ 



*109 26 





to a m, 



Reentrant angle of twin, 







55 42 



55 17 



In their axial ratios the two caesium salts are very similar, 

 as are also the two rubidium salts, while the rubidium com- 

 pounds differ considerably from those of caesium, especially in 

 the relation of a to the other axes and in the angles /?. It is 

 therefore evident that the replacement of one metal by another 

 in these salts has a considerable influence upon their form, 

 whereas, as we have shown, such a replacement in the caesium 

 and rubidium trihalides has little or no effect. There seems to 

 be no regularity in the influence of the replacement of chlorine 

 by bromine in these gold salts, for in the caesium compounds 

 the chloride has a slightly shorter ""axis c and a greater angle j3 

 than the bromide, while in the rubidium salts exactly the 

 reverse is true in both cases. This unexpected relation between 

 the chlorides and bromides has been confirmed by repeating 

 the measurements, especially of the angle m^c, using both 

 crystal and cleavage faces. It is certain that this angle is about 

 a degree greater with the chloride than with the bromide in 



Am. Jour. Sci.— Third Series, Vol. XLIV, No. 260.— August, 1892. 

 11 



