420 Mr. Greville Williams on Emeralds and Beryls. [June 19, 



Prolonged heating gradually diminishes the colour, the bead gradually 

 becoming of the palest bottle-green, and, finally, nearly colourless. This 

 result is the same as with the emerald. 



The metallic oxide which yields the finest tints when fused with 

 opaque beryls, or the artificial mixture, is that of cobalt. The manner 

 in which this oxide withstands the intense heat of the oxyhydrogen flame 

 is remarkable. All tints, from nearly black to that of the palest sapphire, 

 can be obtained, and the resulting glasses, when cut, are extremely beau- 

 tiful, and have almost the lustre of crystallized gems. 



The globules obtained by fusing the artificial mixture of beryl ingre- 

 dients with didymium oxide show the characteristic absorption-spectrum 

 of that metal in a very perfect manner, the lines being intensely black. 

 Even when the bead is quite opalescent from insufficient heating, the 

 black lines are beautifully distinct in the spectroscope. "With a large 

 quantity of didymium oxide the beads are of a lively pink, becoming 

 more intense by artificial light, and, when cut, form very pretty gems. 

 The presence of didymium in sufficient quantity raises the specific gravity. 



Specific Gravity of Artificial Amorphous Beryls containing Didymium. 



No. of experi- 

 ment. 



w. 



W. 



t, 



pt. 



D. 



i. 



•9467 



•5815 



o 



11 



•999655 



2-59 



the resulting number being almost as high as that of the emerald before 

 fusion. 



Conclusions. — The evidence given in this paper, showing that colourless 

 beryls may contain as much carbon as the richest-tinted emerald, taken in 

 conjunction with the ignition experiments, and the results of the fusion of 

 chromic oxide with colourless beryls and with an artificial mixture of the 

 same composition, leaves me no room to doubt the correctness of Yau- 

 quelin's conclusion, that the green colour of the emerald is due to the 

 presence of chromic oxide. 



The fact that emeralds and beryls lose density when fused cannot 

 properly be cited as proving that they have been made in nature at a low 

 temperature ; for it is quite possible that they were crystallized out of a 

 solution in a fused mass, originally formed at a temperature high enough 

 to keep the constituents of the emerald in a state of fusion, and that the 

 crystals developed themselves during a slow process of cooling or evapora- 

 tion. The method employed by Ebelmen * for the artificial production of 

 chrysoberyl, namely heating alumina, glucina, and carbonate of calcium with 

 boracic acid in a porcelain furnace until a portion of the menstruum had 

 evaporated, yielded crystals of the true specific gravity, showing the 



* Ann. Chim. Phys. [3] vol. xxii. p. 223 (1848) ; vol. xxdii. p. 40 (1851). 



