300 
Transactions of the Boyal Society of South Africa. 
former. These two forms are easily visible to the unaided eye. When 
viewed under the lower power of the microscope, the crystals show in 
addition several other forms. These are, apparently : 
1. The basal pinacoid. 
2. Faces presumably belonging to four other tetragonal bipyramids of 
the first order. 
Qualitative chemical tests fully established the presence of titanium. 
The Prominent Tetragonal Bipyramid of the First Order. 
The extraordinary brilliancy of these faces allows of their angles being 
measured with very great accuracy, the Schrauf signal obtained in every 
case being excellent." 
Determination of Angles between the face normals of the faces of the 
First-Order Pyramid. 
Ill A ill = 136° 36' 
111 A 111 = 136° 36' 
The above results were obtained as averages of several readings on 
four different individual crystals, and none of the readings varied from 
the average by a greater amount than +1'. 
From the above values we derive 
001 A 111 = 68° 18'. 
and an application of the usual formula 
tan (001 A 111). 1^2 = (5 
leads to the following value for the axial ratio 
ct:c = l: 1-7769, 
while the standard value given by Goldschmidt in his " Winkeltabellen 
for anatase is 1:1-7771. 
The Tetragonal Bipyramid of the Second Order. 
The faces which constitute this form give fairly good signals. 
Determination of Angles between face normals of Second-Order 
Pyramid. 
A 6"' = 120° 32'. 
e"Ae'^-120° 34'. 
