AT FREIBERG. 



417 



has run out of the first groove that the litharge mould has been filled three times, the groove is closed, and enough 

 refined lead is added to bring the contents of the furnace once more to the old level. Another groove is then cut 

 near the first one, and three moulds are filled through this; after which a third groove is cut still further to the 

 left, etc. After this, when the requisite amount of lead has been added, the first groove is again opened, &c, till each 

 groove has been used three times, at each time filling three moulds of 1(J to 17 centners each, which makes 

 10 ^ 17 = 432 centners. 



The amount of air conducted through both tuyeres per minute is equal to 180 cubic feet. 



The charge of the cupellation furnace during the litharge period requires very great skill and experience from 

 the cupellers. As the surface of the lead sinks more and more, the tuyeres must be more and more inclined to bring 

 the current of air upon it. There seems to be no difference between the chemical constitution of red and yellow 

 litharge. According to the most accurate results yet reached, the proportion of red lead which is obtained appear 

 to depend upon the purity of the lead and the length of time it takes in cooling. 



The nearer the process approaches to the " Blick," the slower is the formation of litharge, till at last it can only 

 be continued by a very strong fire. With the exception of this part of the litharge period, the temperature during 

 that period must be lower than during the formation of " Abstrioh," with which cupellation begins. 



Silvek Blick. — When the molten litharge becomes so small in quantity that it can no longer cover the surface 

 of the silver beneath it, the mass becomes suddenly very bright, and shows the sea-green color of melted silver. 



Figures like (lowers and waves appear on the surface of the molten silver, and are occasioned by the covering of 

 fused litharge forming no longer a continuous sheet on the hath, but, becoming mores and more net-like, while the 

 bright silver below shines more and more through the openings, fill finally the last particles of litharge are driven to 

 the edge of the hearth. This is the juncture to which the name "Silver Blick'' has been applied. As soon as this 

 appearance ensues, the fire is quenched quiokly by throwing pails of water upon it, the blast is stopped and hot 

 water is poured upon the " Blick Silver " by means of an iron trough in order to cool it as rapidly as possible. 



When tho "Blick Silver" to be obtained, is too heavy to bo easily handled, a " silver knife " or thin iron beam 

 with several branching arms on each side, is lowered down into the metal before it hardens, so that it can be easily 

 broken in pieces. Without this arrangement it would he very difficult to break the silver, and considerable loss 

 would bo likely to ensue in the effort to do so. The cover of the cupellation furnace is lifted oil and swung to 

 one side, and the silver is romoved to some place of security until ready for refining. This "Blick Silver" contains 

 still 4 to 5 p.c. of impurities, chiefly copper, lead, and bismuth, the latter having even a, greater affinity for silver than 

 lead. The weight of one of these "Silver Blicks " is from 3 to (1 centners. Only a, small part of the silver goes into 

 tho hearth or elsewhere into the pluinbiferous products of cupellation. 



The solo of the hearth which is soaked with oxide of lead to a, depth of 2 to I! inches, breaks off in separate scales 

 from that portion of the mass into which the litharge lias not, penetrated. It is known simply as "Hearth," and is 

 either treated in the Lead Matt Process as a reagent, or is smelted in oupalo furnaces by itself with coke to a. pure 

 Raw Lead, the earthy constituents of the hearth mass forming a slag very difficult to fuse. The part of the hearth 

 which has not been in contact with the molten litharge is broken up and used together with new material in the 

 formation of the next hearth in tho cupellation furnace. By the treatment of foreign (American) ores, a " Blick 

 Silver" is obtained containing 0.11 to 0.15 p.c. of gold. This is treated by itself. From the cupellation of 350-380 

 centners of pattinsoned KawLead there result 330 centners yellow and red litharge, of which the J to a partis red, and 

 contains about 1.5 p.c. Silver. Red litharge is packed in kegs and sold, while the yellow is reduced to pure lead. The 

 weight of the cupellation hearth is from 38 to 40 centners. 



The "Blick Silver" before reaching the fineness required for the mint must be still further refined. 



Refilling of /Slick Silver,— ThU work consists of a continuation of the cupelling process, whereby the Silver is so 

 far purified from the other metals that it can bo immediately used by the mint without further refining. 



The silver refining furnace in which this operation is conducted very nearly resembles the English roverboratory 

 furnace, but is smaller. It has, besides, a blast through two tuyeres situated near the lire bridge and one on each side 



AMERI. PllILOSO. SOO. — VOL. XIV. — 105 



