1919. No. 4. A CRYSTALLOGRAPHIC INVESTIGATION OF SOME ORGANIC ACIDS. 5 
Forms observed, frequently: a j1oo!, »]110i, u j110l, r}roL|, o JIor|, 
€ joot!, q Joıı|, o }111|, rarely: }ıo2!. 
The crystals are partly elongated along the edge a:r, partly formed 
in tables parallel to a jroo}. 
Fig. 1 shows the two enantiomorphous forms. 
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| 
Fig, r. 
The results of the measurement of angles on t5 species of the dextro- 
form and 12 species of the lævo-form are given in table A. 
Perfect cleavage parallel to a }roo|, imperfect parallel to c joo1!. 
By means of a mixture of alcohol and benzene I have etched figures 
on the face a |100!. These etched figures show distinctly the sphenoidal 
symmetry of the crystals. 
Fig. 2 shows the etched figures on a |100; on the two forms. The 
figure on plate 1 is a microphotography of the etched figures on a |100f. 
Fig. 2. 
The crystals show extinction directions between crossed Nicols parallel 
to the edges a:r and a: m. 
The plane of the optic axes is & jo1roj; 2 E — ca. 46°. 
The first median line lies in the acute angle 8, and inclines 3° to 
the c-axis. 
The d-Phenyiglycerinic acid. 
Melting-point 95 ?. 
Specific gravity: r,419. 
