SILVER ORES. 323 



on account of the thinness of the leaves inlo which it 

 is beaten. A grain of the metal may be made to cover 

 56^ square inches of surface, and the thinnest leaf is but 

 1.280,000th of an inch thick. 



Perfectly pure gold is denominated gold of 24 carats, or 

 Une gold. If it contains 22 parts of pure gold to 2 of silver, 

 or to 1 of copper and 1 of silver, it is said to be 22 carats fine ; 

 so also for 20 carats fine, it contains 20 parts of pure gold. 

 The carat is divided into £, \, ^ , ^ parts, for a more min- 

 ute specification of the quality of gold. * 



The standard gold of the United States consists of 900 

 parts of gold to 100 of an alloy of copper and silver. The 

 eagle (10 dollars) contains 232 grains of fine gold. 



Aurotellurite, called also Sylvanite, is a grayish or silver-white 

 mineral, containing gold combined with Tellurium. 



3. SILVER. 



Silver occurs native and alloyed ; also mineralized with 

 sulphur, selenium, arsenic, chlorine, bromine, or iodine, and 

 in combination with different acids. 



The ores of silver fuse easily and decompose before the 

 blowpipe, affording a globule of silver either alone or with 

 soda ; the globule is known to be silver by its flattening 

 out readily under a hammer, and also by its sectility. The 

 species vary in specific gravity from 5*5 to 10*5. 



NATIVE SILVER. 



Monometric. In octahedrons. No cleavage apparent. 

 Occurs often in filiform and arborescent shapes, the threads 

 having a crystalline character ; also in laminae. 



Color and streak silver- white and shining. Sectile. Mal- 

 leable. H=2-5— 3. Gr=10-3— 10-5. 



Composition : native silver is usually an alloy of silver and 

 copper, the latter ingredient often amounting to 10 per cent. 

 It is also alloyed with gold, as mentioned under that metal. 

 A. bismuth silver from Copiapo, S. A., contained 16 per cent, 

 of bismuth. 



What surface may a grain of gold be made to cover 1 How much 

 ure gold is there in the American eagle 1 What is the use of tha 

 erm carat 1 What is the condition of silver in nature 2 Describe na- 

 tive silver. 



