24 
DR. A. E. H. TUTTON ON THE 
% 
Ammonium Manganese Sulphate , (NH 4 ) 2 Mn(S0 4 ) 2 . 6H 2 0. 
Morphology. 
Crystals of this salt were measured by Murmann and Rotter ( loc. cit., p. 148), and 
also to some extent by Grailich* and by ScAcemf. The results of Mtjrmann and 
Rotter are given in the next to the last column of the table of angles, and those of 
Grailich (G) and of Scacchi (S) in the last column. 
Crystal System. —Monoclinic. Class No. 5, holohedral-prismatic. 
Ratios of Axes .— a :h : c — 07400 : 1 : 0‘4931. Values of Murmann and Rotter, 
07359 : 1 : 0'4972. 
Axial Angle .— (3 = 106° 51'. Value of Murmann and Rotter, 107° 2'. 
Forms observed .— a{l00}, h { 010 }, c{00l}, p {110}, p'{l20}, p"'{\2>0}, q {Oil}, 
r'{2l0}, o {111}, o'{Til}. Murmann and Rotter also found a minute face of 
n' {121} on one crystal. 
Habit .—Prismatic (primary prism j»{ll0}) parallel axis c. The prisms are 
sometimes fairly long, but more frequently short. 
Ten good crystals were measured, obtained from five different crops. The results 
are given in the table of angles. The crystals were beautifully transparent in the 
crops retained for use, but some other crops showed an appreciable amount of 
turbidity. They are not quite colourless, a faint pink tint appearing to be an 
essential property of the salt which in the cases of truly transparent crystals renders 
them very beautiful, especially when a number are seen together against a white 
background. Great care is required in growing them for goniometrical purposes, as 
crops grown without the precautions indicated in the author’s “ Crystallography and 
Practical Crystal Measurement ” (p. 9) show more facial irregularities than many 
other salts of this series. 
The primary prism p {110} is generally the largely predominating 
form, closely followed by the basal plane c {001}, as shown in fig. 1. 
Often, however, the latter form c is less prominent, the faces of 
q {011} being relatively larger and the orthopinakoid r'{20l} being 
exceptionally well developed, as shown in fig. 6. Occasionally 
crystals were also seen, and one was measured, having large b {010} 
faces. The hemipyramid faces o' {ill} (common) and o {ill} (rarer) 
were usually somewhat distorted, rarely giving images of the signal 
so good as those derived from the faces of other forms. The 
prismatic form p'{l20} was fairly common, appearing as a strip, but 
the prism p"'{ 130} was much more rarely developed. The orthopina¬ 
koid a {100} was only once seen, and was then merely a fine narrow strip affording an 
image too faint for absolute measurement. The face n'{T21} recorded by Murmann 
* ‘ Krystallogr.-optische Untersuehungen, Preiaschr. Wien,’ 1858, 140. 
t ‘II Giambattista-Vico, Giomale Scientifico,’ Naples, 1857, fasc. 6, sep. 9. 
