8 8 'Andyfts of Gens. [Book VI. 



The precious (tones are chiefly compofed of the 

 argillaceous and filiceous earths ; of which the former 

 predominates. Some diamonds alfo are thought to 

 contain a portion of earth, but thefe cannot properly 

 be accounted diamonds. 



On diffblving the very fubtile powder of the gems 

 in a double weight of vitriolic acid highly concen-j 

 trated, the refiduum, after evaporation, being -.vafhed 

 with warm water, yields a metallic colouring fubftauce, 

 and a fmall portion of lime. The metallic part, pre- 

 cipitated by what was in the old chemical nomenclature 

 called a phlogiilicated alkaline lixivium, yields a beau- 

 tiful Pruffi.an blue ; hence we conclude that the red 

 colour of the ruby, as well as the blue of the fapphire, 

 the yellow of the topaz, the tawny of the hyacinth, 

 and the green of the emerald, are to be attributed to 

 iron *. 



Bergman obtained by analyfis, from one hundred 

 parts of the following precious ftones : 



Clay. Flint. Lime. Iron. 



Emerald, 60 24 8 6 



Sapphire, 5 s 35 5 2 



Topaz, 46 39 8 6 



Hyacinth, 40 25 20 13 



Ruby, 40 39 9^ 10 



From the above it may be collected, that the gems 

 agree in this refpect, that they all confift of the fame 

 principles j and that of thefe the argillaceous earth 

 forms the greateft part, then the filiceous, next the 

 calcareous, and leaft of all the ironf. The gems, 

 Except the emerald and hyacinth, refill the moft in-. 



* Bergmaij's Diflertations, p, 15. 

 f Chemical Effays, Diff. 15. 



tenfe. 



