740 The American Naturalist. [September, 
hydrochloric, sulphuric, nitric, phosphoric and oxalic acids.—Dupare 
and Pearce’ have measured the crystal angles and observed the optical 
properties of eight new chemical compounds. These are benzoyl-malic 
acid, sodium orthophenyl-benzoate, potassium orthophenyl-benzoate, 
ammonium phenyl-glycolate, dextrocinchonine pheny]-glycolate, ben- 
zylic ether of bromo-tolu-quinone oxime, potassium luteo-phosphomo- 
lybdate and a potassium luteo-phosphotungstate. 
Of late numerous additions have been made to our knowledge of 
the crystallographic and optical constants of organic compounds. The 
following three papers in Volume XXV in the Zeitschrift fiir Krystal- 
lographie may be cited asimportant contributions to this line. 1. The 
Crystal form of Some New Halogen Derivatives of Camphor, by F. S. 
Kipping and W. J. Pope; 2. On the Crystal Form of Some Organic 
Compounds, by W. J. Pope; 3. Crystallographic and Optical Investi- 
gations on Some Organic Compounds, by E. A. Wiilfing. 
An artificial cassiterite investigated by Arzruni’® shows distinct 
dichroism with the ray vibrating parallel to the vertical axis colorless, 
while the ray vibrating at right angles thereto is pink. The erystals 
reach a half centimeter in thickness and twice that in length. Twins, 
which are socommon with natural cassiterite, were not observed. The 
angles measured coincide within 2’ with those given by Becke for the 
natural mineral. The mean values from two determinations of the in- 
dices of refraction are: : 
Li Na Tl 
w 1.9846 1.9968 2.0093 
E 2.0817 . 2.0929 2.1053 
These numbers agree as well as could be expected with those ob- 
tained by Grubenmann for cassiterite, showing that the natural and 
artificial products are practically identical. 
Schmidt" gives at great length tables showing the recurrence of like 
interfacial angles in the regular system. As an extreme example, the 
angle 35° 15’ 52” occurs between eleven pairs of faces, the cube, octa- 
hedron or dodecahedron constituting one face of each pair. The table 
at the end of the paper may be of use for rapidly identifying rare faces 
on regular crystals. 
Sohncke”™ shows that in accordance with his views of crystal structure 
no circular polarization is to be expected in crystals of the pyramidal 
1? Zeitschr. f. Kryst., XXV, p. 529, 1895. 
