1919. No. 4. A CRYSTALLOGRAPHIC INVESTIGATION OF SOME ORGANIC ACIDS. I3 
The interference figure seen through a jrooi, demonstrates the twin- 
ning parallel to a ;100;. 
The active acids. 
Melting-point 138 ?. 
Specific gravity d-acid r,700, lacid r,700. 
Class of symmetry: monoclinic-sphenoidal. 
Axial angle 8 — 949 5. 
Ratio of axes: a:b:c— 1,9840:1:0,8543. 
The crystals are elongated along the edge a:r. 
Forms observed: a j100l, m irro|, ge j11oj, s |rorj, 0 |10T}, c }301!. 
Faces of the fourth order are frequently developed, but they are not 
measureable. The appearance of the crystals is about the same as that of 
the two isomeric acids (Fig. 5 a and b). 
The measurement of the angles are given in table F. 
Cleavage perfect parallel to a |1ooi, imperfect parallel to 2 joro}. 
The etched figures on the face a \100! show the enantiomorphism of 
the d- and the l-acid. 
The plane of the optic axes is 4 jo10{; 2E = ca. 88°. 
The first median line lies in the obtuse angle 8 and inclines ca. 10 ? 
to the c-axis. 
As may be seen from the measurements of the two Phenyl 3-bromo 
«-hydroxy-propionic acids and their components, there is a great con- 
formity between these stereoisomeric compounds in all their crystallogra- 
phic properties. This is an interesting fact, the chemical properties also 
being very similar. The chemical investigation of these compounds will 
be published shortly in Ber. d. deutsch. chem. Ges. 
The melting-point curves between the inactive and the active form of 
the two Phenyl 3-bromo a-hydroxypropionic acids are: 
Between the inactive acid m. p. 165? and its d-component: 
100 ?/, rac. acid o 9/; d-acid m. p. 1659 
du => » 23.* « » 150 0 
LX e ME. 50 » » » — 140,5" 
SUE CM T para “2393 
25» » » 715° > » 138 ? 
OL. r$ » IOO » » » 143 0 
