Mr. Greville Williams on Emeralds caul Beryls. 325 

 Specific Gravity of Artificial Amorphous Beryls containing Didymium. 



No. of experi- 

 ment. 



w. 



W. 



t. pt. 



D. 



\A 



•9467 



•5815 



1°1 j -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 co- 

 lourless 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 Vauquelin'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 du- 

 ring a slow process of cooling or evaporation. 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 eva- 

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

 density of minerals to be less dependent on the temperature at 

 which they are produced than upon their crystalline or amorphous 

 state. 



One crystalline gem (the ruby) has undoubtedly been produced 

 in nature at a high temperature. I have frequently repeated 

 Gaudin'st experiment on the artificial formation of this stone, and 

 can confirm most of his results. I did not, however, find the density 

 to be quite the same as that of the native ruby or sapphire, which 

 is, in different specimens, from 3'53 to 3-56. Artificial rubies of 

 the finest colour made by me by Gaudin's process had a specific 

 gravity of 3-45, which is not three per cent, lower than that of the 

 ruby. The reason for this close approximation will be found in 

 the fact that fused alumina crystallizes on cooling. The crystalli- 

 zation, however, is confused and imperfect, which causes the re- 

 sulting product to be only partially transparent, and to have a 

 slightly lower specific gravity than the natural gem. It is, conse- 

 quently, scarcely correct to call the fused stones made by Gaudin's 

 process " artificial rubies." 



I have convinced myself that rubies have been formed in nature 

 at a temperature equal, or nearly equal, to that of the fusing-point 

 of alumina, from the circumstance that the reaction between chromic 



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

 t Ann. Pharni. vol. xxiii. p. 234. 



