34 
DR. A. E. H. TUTTON ON THE 
Ammonium Copper Sulphate , (NH 4 ) 2 Cu (S0 4 ) 2 . 6H 2 0. 
Morphology. 
Crystals of this salt were measured in the year 1835 by Miller, # who observed the 
forms a, c, p, q, r', and o', of those enumerated in the list of forms given below. 
Murmann and Plotter included the salt in their optical investigation of 1859 ( loc. cit., 
p. 170), and observed the further forms h and p' ; but they did not record any accurate 
measurements of the crystal angles. Miller’s values are quoted in the last column 
of the table of angles now given. 
Crystal System. —Monoclinic Class No. 5, holohedral-prismatic. 
Ratios of Axes .— 
a : h : c — 07463 : 1 : 07066. Values of Miller, 07433 : 1 : 0'4838. 
Axial Angle. —/ 3 = 106° 9'. Value of Miller, 106° 6b 
Forms observed .—ct {100}, b {010}, c {001}, p {110}, p'{l20}, p"'{l2>C\, q {Oil}, 
r'{20l}, o {111}, (/{Til}. 
Habit .—Short prismatic parallel to p {110}, or tabular parallel to c {001}. 
Eleven perfectly transparent crystals were measured of this beautiful pale blue salt, 
selected from seven different crops. They were of the two types shown in figs. 8 
and 9, and of intermediate types. 
Fig. 9. 
Many crystals of the numerous crops prepared were very simple, exhibiting only 
the forms c {001}, p {110}, q {Oil}, and r'{20l}. On numerous others small or 
narrow representatives of the other forms mentioned in the list of forms were present. 
On a good number of the crystals of the crops from which individuals were selected 
for measurement there were well developed faces of the clinopinakoid b {010}, the 
rarer prisms p'{ 120} andp w {l30}, and the hemipyramids o {111} and (/{Ill}. Traces 
only of the orthopinakoid a {100} were observed, no measurements being possible. 
The variation of the length of the faces of the prism zone causes the variation of habit 
from prismatic along p {110} to tabular parallel to c {001}. Both these forms showed 
striation in many of the crops prepared, but the crops used were composed of crystals 
exhibiting this property at a minimum, and several of the measured crystals were 
quite free from striation. The face in contact with the bottom of the crystallising 
vessel had been either p or c. 
* ‘Phil. Mag.’ 1835, [3], 6, 105; ‘ Pogg. Ann. der Phy., 1835, 36, 477. 
