WHERRY AND ADAMS: PINAVERDOL 397 



methane, and the isomeric "i6"o-cyanine iodide" is the corre- 

 sponding form of the hydriodide of 4,2'-diquinolyl methane — 

 that is, it differs from cyanine iodide in that the second (or 

 primed) quinoHne nucleus is attached at the carbon atom ad- 

 jacent to the nitrogen, instead of at the one diametrically op- 

 posite. 



Prior to 19 14 this dyestuff was made only in Germany, but 

 is now being produced both in England and the United States. 

 The present paper consists of a detailed description of the crys- 

 tallography and optical properties worked out for the purpose of 

 testing the identity of these several preparations. 



CRYSTAIvIvOGRAPHY 



The crystals from different preparations of pinaverdol exhibit 

 considerable variation in habit, ranging from markedly prismatic 

 to thinly tabular. Orientation of the different types is made 

 easy, however, by the brilliant and striking reflection-pleo- 

 chroism present. There are two prominent zones of faces, lying 

 at right angles to one another, and all of the forms in one of them 

 reflect brass-yellow light, while the dominant forms in the other 

 yield beetle-green reflections. The former zone has been taken 

 as the prismatic one, and the latter held right and left. The 

 crystal system then proves to be monoclinic, although since the 

 base lies but 1° 40' away from the pole of the prism zone, and 

 the plus and minus orthodomes are often about equally de- 

 veloped, it is decidedly close to the rhombic system. According 

 to current usage, it would perhaps be described as "pseudo- 

 rhombic," but it seems to the writers desirable to use prefixes 

 which express more definitely the true relationships.^ In ac- 

 cordance with the plan we have proposed, pinaverdol would be 

 described as "lepto-monoclinic, but peri-rhombic." It may also 

 be noted that according to Fedorov's usage, since the prism angle 

 is 84° 30', that is, nearer 90° than 60°, this substance would be 

 classed as hypo-tetragonal or tetragonoidal. 



About 20 crystals of all habits were measured on the Gold- 



' Journ. Wash. Acad. Sci. 9: 153. 1919. 



