Mr. J. Napier on Copper Smelting. 35 



which cannot be increased without affecting the slag, and the 

 length of time required for fusing. What ought to constitute the 

 proper size of charge, or furnace, or length of time, it would be 

 difficult to fix as a rule ; but the following results, coming under 

 our own observation, may give a better idea of the principles we 

 are here stating. 



1st. The furnace hearth measured 11^ by 8 feet, had 25 cwt. 

 calcined ore, 7 cwt. of slag and cobbing asthe charge, and delivered 

 5 charges in the 24 hours, equal to 6 tons ore per day. The 

 foul slag, with shots in it to be returned, averaged 2^ cwt. each 

 charge. The clean slag contained fully fths per cent, copper. 

 The mistake in these operations was allowing too little time; 

 for fusing each charge it could not exceed 4 hours. Average of 

 coal consumed per week 20 tons. 



2nd. A furnace 12 x 8|^ feet inside measure, charged with 

 31 cwt. of ore and 9 cwt. of slag and cobbing, delivered 4 

 charges in the 24 hours, equal to 6 tons ore per day, each charge 

 taking about 5-^ hours time. The foul slags with shots averaged 

 2 cwt. per charge ; the clean slags contained under \ per cent, 

 copper. Coals consumed weekly 21 tons. 



3rd. Furnace measured 13 J by S~ feet inside, charged with 

 36 cwt. of ore and 9 cwt. of slag and cobbing, 4 charges in 24 

 hours, equal to 7 tons of ore per day. Average foul slags with 

 shots 3 cwt. per charge ; the clean slags contained \ per cent. 

 Average coal consumed weekly 23 tons. 



One furnace of the ordinary size, working four weeks, fusing 

 each charge 31 cwt. ore and 9 cwt. of slag and cobbing, gave as 

 an average \~ cwt. foul slag each charge, and slags thrown 

 away containing -28 per cent, copper. The same furnace working- 

 other four weeks, but fusing each day 36 cwt. of ore and 9 cwt. 

 of foul slag, gave an average of 3J tons foul slags each charge, 

 and the slags thrown away had "38 per cent, copper. Here were 

 two evils; more foul slag to be refused, and more copper cast 

 away : the extra coal for the month was 5 tons. The loss here 

 is about £7, the gain is 28 tons more ore fused, costing 5^. per 

 ton, besides the drawback of the furnace being more liable to 

 get out of repair. 



These few examples will suffice to illustrate the principles of 

 management. A great number might be enumerated where the 

 apparent gain on one point was accompanied by losses on some 

 other. We have seen ore-fusing furnaces measuring 19^ x 11 J, 

 with a charge, including slag and cobbing, of 90 cwt., and 

 fusing four of these in 24 hours ; but the quantity of slags to be 

 returned was so great, that the furnace, to fuse its own foul slags, 

 which a furnace should, could only take in one-half the charge 

 of ore, and consumed upwards of 30 tons of coal per week. 



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