1919. No. 4. A CRYSTALLOGRAPHIC INVESTIGATION OF SOME ORGANIC ACIDS. 9 
The racemic acid. 
Melting-point 165 ", 
Specific gravity 1,676. 
Class of symmetry: monoclinic-prismatic or monoclinic-domal. 
Axial angle $ — 92° 42’. 
Ratio of axes: a:b:c = 1,822:1:0,999. 
Al| the crystals examined are twins, with 
the face a (100) as a twin plane. (Fig. 4). 
The twin nature is betrayed by the presence 
of a re-entrant angle between the two basal 
planes. 
Forms observed: a |100!, c jooM, m j110\, 
P i310, x 112, v [1er]. 
The measurements of the angles on 15 spe- 
cies gave: 
Table C 
| No. of | : 
Angle Measure- Limits pen Calculated 
| : observed 
ments | 
(100) : (110) 22 599 24'— 62? 48‘ 610 r12°* — 
(100) : (oor) 22 | 86 3—87 35 | 87 18° | _ 
foro}: [ort] 7 26 23 —26 47 26 34* — 
(r00):(310) | 26 29 30 —32 10 30 45 310 14' 
(too): (127) | 9 | Tj 297029 71 48 | 71 20 
(roo) : (1127 8 | 71 517—719 48 18 59 | 78 40 
[oo:]:[oro] | get 62 3563 53 63 ıı 63 26 
[oor] : {oro} get 89 38—9o 30 90 Io go o 
I 
Cleavage imperfect parallel to 2 joro! and c joo1!. 
The plane of the optic axes is nearly perpendicular to the face 
a (100). The first median line lies in the a—c plane. 
Through a j1o0oj, by using convergent light and an immersion oil of 
high refractive index, an interference figure is seen, demonstrating the 
twinning parallel to a }ıoo|. 
The active acids. 
Melting-point 143 °. 
Specific gravity: d-acid 1,700; l-acid 1,700. 
Class of symmetry: monoclinic-sphenoidal. 
