1910. No. 4. A CRYSTALLOGRAPHIC INVESTIGATION OF SOME ORGANIC ACIDS. 7 
The crystals are obtained from a solution in methylal-benzene. 
Class of symmetry: Monoclinic-sphenoidal. 
Axial angle 5 = 90° 4o*. 
Ratio of axes: a:b:c = 2,5408: 1: 2,2216. 
Forms observed: a jroo|, 7 irorj, o |rotj, m ix10j, u }1To, c jooti. 
Faces of the fourth order are rarely developed but they are not 
measureable. 
Cleavage, imperfect parallel to m j110| and c joo1!. 
The measurement of angles on 16 species gave: 
Table B 
| No: of | 
Angle | Measure- | Limits Mean Calculated 
| observed 
ments 
| | 
: : | 
(roo) : (ror) II 470 51'—4099 o' | 480 27'* — 
| 
(100):(ro1) 14 48 19—49 52 | 49 12 * -— 
(100) : (110) 17 68 9-68 56 | 68 31 * — 
(100) : (oo1) 14 88 59 —89 :8 89 41 | 899 20' 
[oto] : [oor] 10 89 53 —90 24 90 10 | co o 
In fig 3 are shown the general appearance of the crystals. 
The etched figures on the face a }100! show the sphenoidal sym- 
metry. 
The plane of the optic axes is 4 jo1o!; 2 E — ca. 94°. The first 
median line is nearly parallel to the a-axis. 
Knowing the axial angle, the axial ratios and the density of the cry- 
stals of the two Phenylglycerinic acids, I am able to calculate the mole- 
cular distance ratios y, w and w of the two acids. For this purpose I 
