1873.] Mr. Greville Williams on Emeralds and Beryls. 417 



rior to that of the emerald. The green beads may, by an intense and 

 prolonged heat, be rendered colourless. With cobalt oxide the beads 

 afford beautiful blue glasses of any desired shade ; and in all cases the 

 results are the same as with the artificial mixture of beryl ingredients to 

 be described further on. 



The effect of fusion upon the beryl is to lessen the hardness and 

 lower the specific gravity. The globules may be scratched by quartz. 

 The following numbers were obtained in a determination of the specific 

 gravity :— 



Specific Gravity of Beryl A after fusion. 



No. of experi- 

 ment. 



W. 



W. 



t. 



pt. 



D. 



I. 



II. 



2-3376 

 2-3376 



1-3710 

 1-3699 



27-2 

 27-0 



•996603 

 •996603 



2-41 

 2-41 



The beryls have, therefore, lost nine per cent, of their density in pass- 

 ing from the crystalline to the vitreous state. 



I was desirous of carefully comparing this loss of density undergone by 

 beryls with that of rock-crystal fused under the same circumstances. 

 According to an experiment quoted by Forbes*, the specific gravity of 

 quartz of undoubted aqueous origin, and also that from granites, is 2*6, 

 and that of rock-crystal, fused before the oxyhydrogen blowpipe to an 

 amorphous glass, 2-2. According to the experiment of Le Eoyer and 

 Dumas f, the specific gravity of rock-crystal determined at 4° in vacuo 

 was 2-652. The value found by the Austrian Commission was 2-651223J . 

 I have repeated with great care the determination of the specific gravity 

 of rock-crystal, both before and after fusion, with the annexed results : — 



Specific Gravity of Bock-crystal before fusion. 



No. of experi- 

 ment. 



W. 



W. 



t. 



pt. 



D. 



I. 



1-9493 



1-2154 



o 



21 



•998047 



2-65 



The above number is practically identical with those of Le Eoyer and 

 Dumas and the Austrian Commission. Bock-crystal fuses very readily 

 before the oxyhydrogen blowpipe, and, if care be taken, the beads ob- 

 tained are beautifully clear and free from bubbles. 



* Chem. Soc. Journ., new series, vol. vi. p. 225. 



t Gmelin's 'Handbook of Chemistry,' vol. iii. p. 354. 



| Ueber das Verhaltniss des Bergkrystall-Kilogrammes zum Kilogramme der K. 

 Archive zu Paris (Wien, 1870). I am indebted to Prof. W. H. Miller for this re- 

 ference. 



