2 
DR. A. E. H. TUTTON ON THE 
Ammonium Nickel Sulphate, (NH 4 ) 2 Ni (S0 4 ) 2 .6H 2 0. 
Morphology. 
The first measurements of the crystals of this salt were made 60 years ago by 
Marignac,* and the salt was included four years later by Murmann and Rotter} 
in their comprehensive crystallographic investigation. The forms observed in both 
investigations were the same as those given in the list below, except a {100} and 
o {ill}, and the values observed for the principal angles will be found quoted in the 
two last columns of the table of angles. 
Crystal System. —Monoclinic. Class No. 5, holohedral-prismatic. 
Ratios of Axes.—a : b : c = 07373 : 1 : 0'5000. Values of Murmann and Rotter, 
07370 : 1 : 0‘5032. 
Axial Angle.—ft = 106° 57'. Value of Murmann and Rotter, 107° 4'. 
Forms Observed.—a {100}, b {010}, c {001}, p {110}, p' {120}, q {Oil}, A {201}, 
o {111}, o'{Ill}. 
Habit. —Short prismatic parallel p {110}, or more or less tabular parallel to a pair 
of faces of this prism (developed more than the other pair), or parallel to c {001 1 . 
Ten excellent small and perfectly transparent crystals of this magnificent bluish 
emerald-green salt were measured, selected from six different crops. The results are 
shown in the accompanying table of angles. 
The crystals were of the two types illustrated in figs. 1 and 2. 
The characteristic of the first type is the predominance of the primary prism 
p {110} and the basal plane c {001}, with smaller faces of the clinopinakoid b {010}, 
the clinodome g{01l}, the form r'{20l}, and the two hemipyramids o{lll} and 
o'{Ill}. The whole of the faces of the two latter forms were never found on anyone 
crystal, and usually only one or two such faces were present. The form r'{20l} was 
also very subsidiary, and on many crystals only one of the two faces was present. 
* ‘ Mem. Soc. Phys. Geneve,’ 1885, vol. 14, p. 247. 
t ‘Sitz. Ber. Akad. Wiss. Wien,’ 1859, vol. 34, p. 158. 
