SILVER ASSAYING 



817 



The Production of Silver in the United Kingdom has been as follows in the last five 



years. 



The Silver Imported in 1873 was as follows: 



Tons 

 837 

 1,479 

 106 

 158 

 691 



Bolivia 4,270 



Chili 4,100 



Other countries . 305 



From Spain .... 

 United States of America 

 Mexico, . . 

 New Granada . . 

 Peru . . 



Total 



11,946 



Value 



22,000 



163,197 



16,019 



10,869 



45,027 



405,155 



342,066 



16,260 



1,020,593 



SILVER ASSAYING. This may be conveniently divided into: 1. The 

 assaying of silver ores ; 2. The assaying of silver and its alloys. 



1. The assaying of silver ores. The ores are reduced to fine powder, and passed 

 through a sieve of 80 holes to the linear inch, and any residual metalliferous particles 

 carefully collected and submitted to a separate assay. The total weight of the sample 

 is ascertained, in order that the proportion of silver obtained from the residiie may be 

 calculated. The sifted portion is well mixed, and submitted to assay by one of the 

 following methods : 



a. Fusion Method. This process is conducted in crucibles, in an air-furnace similar 

 to that described in fig. 533, p. 941, vol. i. (See COPPER.) 



In the assay of silver ores not containing lead, it is usual to obtain the silver they 

 afford in the form of an alloy with lead ; and this is subsequently passed to the cupel 

 in the ordinary way. For the assaying of lead ores containing silver, see LEAD. 



Ores of silver in which the associated metals exist in the form of oxides are com- 

 monly fused with a mixture of litharge or red lead, and powdered charcoal, by which 

 an alloy of lead is obtained, which is afterwards treated by cupellation. The amount 

 of litharge employed must be varied according to circumstances, as the resulting 

 button should not be too small, since in that case a portion of the silver might be lost 

 in the slag ; nor too large, as the cupellation would then occupy a longer time. 



In most cases, if from 100 to 400 grains of ore bo operated on, a button of 200 

 grains will be a convenient weight for cupellation ; this may be obtained by the addi- 

 tion of 400 grains of litharge, and from 7 to 8 grains of pulverised charcoal. This is 

 to be well mixed with 200 grains of carbonate of soda, and introduced into an earthen 

 crucible, of which it should not fill more than one-half the capacity. This is covered 



VOL. III. 3 G 



