520 Prof. A. Ogg and Mr. Lloyd Hopwood : Critical Test 



Taking the mass of the hydrogen atom as 1*64 x 10~ 24 grm., 

 the mass of unit rhomb, if it contains 4 molecules, is 



4 x 173-04 x 1-64 xl0~ 24 or 113'51 x 10" 25 grm., 



and abc x 2-666 = 113'51 x 10~ 25 ; 



and hence, from the known ratios of a : b : c, we find 



a= 5-731 xlO" 8 cm., 

 6 = 10-008 xlO" 8 cm., 

 c= 7-424 xlO" 8 cm. 



The equality in the values of d 1Q0 and a shows that the 

 assumption made in our calculation, that there are 4 molecules 

 in the elementary cell, is correct. 









Table I. 









Crystal. 



Molecular 

 weight. 



Density at 

 20°/4°. 



Molecular 

 volume. 



Axial ratios. 

 a : b : c. 



K 2 SO A 



173-04 

 131-20 

 265-14 

 359-14 



2-666 

 1-772 

 3615 



4-246 



6491 



74-04 

 73-34 



84-58 



0-5727 : 1 : 0-7418 

 05635 : 1 : 0-7319 

 0-5723 : 1 : p-7485 

 0-5712 : 1 : 0-7531 



(NH 4 ) 2 S0 4 



Kb S0 4 



Cs 2 S0 4 







Crystal. 



Length of sides of unit rhomb. 



Volume of 

 unit rhomb. 



a. 



b. 



c. 



K 2 S0 4 



cms. 

 5-731X10 



5-951 xlO" 8 



5-949 XlO" 8 



6-218X10" 8 



cms. 

 10-008x10" 



10-560 XlO" 8 



10-394 xlO" 8 



10-884 XlO" 8 



cms. _g 

 7-424x10 



7-729 XlO" 8 



7-780 xlO" 8 



8-198 XlO" 8 



Cm ' 3 24 



425-78x10 

 485-71 XlO" 24 

 481-14X10" 24 

 554-88 XlO" 24 



(NH 4 ) 2 S0 4 



Rb 2 S0 4 



Cs 2 S0 4 

















In Table I. the volumes of the elementary cells, and the 

 relative and actual values of the lengths of their sides, are 

 shown for the whole series of crystals. 



The most striking fact disclosed by the above table is the 

 very close agreement, almost amounting to identity, in the 

 volumes of the unit rhombs of rubidium sulphate and 



