On Gems. 501 



flower colour ; the third a pale red inclining to violet ; and 



the fourth of a reddish yellow colour. 



Vauquelin's analysis of the oriental ruby gives 

 Alumine - - , - 86-00 

 Magnesia - - - 8*50 



Chromic acid - - 5- 25 



99-75 



The Sapphire. 



The sapphire is a precious stone of a transparent blue co- 

 lour, and is the hardest next the ruby : the oriental sap- 

 phire and that of Puy have the form of two very long hexa- 

 edral pyramids, joined, ind opposed base to base without 

 the interposition of a prism. Sapphires have been found 

 of a rhomboidal form. 



The specific gravity of the sapphire of Puy is in propor- 

 tion to water as 40-769 to 10-000; that of the white sap- 

 phire is as 39*91 1 ; and the Brasilian as 31-307. 



The sapphires from d'Expaily have a green tinge, and 

 change in the fire in the same manner as those of the Bra- 

 sils ; whereas the oriental sapphire is not altered in our fur- 

 naces. The action of oxygen gas upon this stone gives a 

 perfect white opakc globult;. 



A good sapphire of ten carats is valued at 50 guineas ; if 

 it weigh twenty carats, its value is 200 guineas ; but under 

 ten carats it may be valued by multiplying the carat at tea 

 shillings and sixpence into the square of its weight. 



They are found, as well as rubies, in the East Indies, 

 Brasil, Hungary, Silesia, Bohemia, and also in Siberia. 



The analysis by Bergman and by Klaproth : 



100 



The Emerald. 



The emerald is a gem of a fine, full, transparent green 

 colour, elec'rical by friction. It is next in hardness after 

 the topaz. The Peruvian emerald crystallizes in hexaedral 

 prisms truncated, flat at each cxtrenjitw Crystals of eme- 

 rald 



