Moses — Tests \i,pon the Synthetic Sapphires of Verneuil. 273 



near 90°. These are shown in the accompanying cut with a 

 magnification of 225 diameters and strongly snggest the planes 

 of separation parallel lOll described by Bauer* in true sapphire 

 for which the angle is 93° 59'. 



Doicble Refraction and Indices of Hefraction. — Sections 

 were made from the uncut cone and polished and the " tables" 

 of foiir of tlie lai'ger cut stones were used directly. For each 

 surface the direction yielding the largest and smallest indices 

 was determined by trial. The instrument used was the latest 

 form Abbe crystal refractometer, the liquid a solution of 

 sulphur in methylene iodide with ?i = l'784, and the temper- 

 ature 20° C. The sodium flame was used. 



Surface parallel cone axis I'VCTS I'YeoO 



Surface perpendicular cone axis 1"7684 1-7600 



Cut stone table 1-7676 1-7580 



" " " 1-7678 1-7598 



" " " 1-7683 1-7592 



" » " 1-7684 1-7598 



"We may, therefore, take as the most probable values for syn- 

 thetic sapphire the averages 



b> 



= 1-7680 e = 1-7594 and w-e = -0086 



For natural sapphires tlie following results with sodium 

 light are recorded : 



u e u-e 



Sapphire from Ceylon (Brauns) 1-7693 1-7610 -0083 



Sapphire from Burmah (Melczer) 1-7692 1-7609 -0383 



Pleochroism. — Yer^' noticeable with the deeper blue stones, 

 ft) indigo blue as in true sapphire, e pale blue but without the 

 greenish and yellowish tints often noticed in the true sapphires. 



Interference Figxire and Optic Axis. — In finely crushed 

 material a negative apparently uniaxial interference figure was 

 obtained on several different grains. 



Two surfaces were then polished on the conical mass approxi- 

 mately at right angles to each other, the direction in each 

 determined which yielded the smallest extraordinary index and 

 a section about 2™"' thick was made as nearly as- possible 

 parallel to the plane of these two directions, such a section 

 being approximately perpendicular to the optic axis of the 

 cone. The section yielded a distinct, many ringed, but 

 eccentric interference figure optically negative. A thinner 

 section ground until the figure was nearly central showed 

 anomalies, being apparently true uniaxial in one portion but 

 *Zeitschr. d. Geol. Ges., xxvi, 192, 1874. 



