Mr. J. Napier on Copper Smelting. 81 



From 25 to 30 cwt. of calcined ore. 



From 7 to 9 cwt. of sharp slag from more advanced operations. 



From 2 to 3 cwt. of cobbing. 



If the ore is known to be stiff, a box of lime or fluor-spar is • 

 added; but if flux can be avoided, it is better. 



When the charge is let down into the furnace, it is spread 

 equably over the bottom, and the doors all closed, stopping every 

 air-hole with clay, and the heat of the furnace increased as 

 rapidly as possible. In the chimney immediately above and 

 opposite the reverberator is a small hole, through which the 

 workman looks and ascertains the condition of his heat. A 

 similar hole in the door-plate looking into the hearth enables 

 him to judge of the state and condition of the charge. This 

 mode of ascertaining the state of the furnace requires some 

 experience ; but it is of great practical value, as it prevents the 

 necessity of opening doors by which the furnace would become 

 cooled. 



After about five hours' firing, when the furnace has reached a 

 white heat and all appearances are favourable, the door-plate is 

 removed and a long iron rake passed through the fused contents 

 to make sure that the whole is perfectly fused. This being the 

 case, the workman begins the operation of skimming, that is, 

 drawing off the scorise or slag, which from its less specific gravity 

 floats on the surface of the mat, which is effected by means of a 

 long rake, the scorise being drawn out at the front door. This 

 operation requires considerable experience and care in drawing 

 the rake along the surface of the metal, so as not to take out 

 any of the metal with the slag. When the furnace is skimmed, 

 the common practice is to let down a second charge of ore, fuse 

 and skim in the same manner before tapping the furnace to let 

 out the metal. The tap is in the side of the furnace, and is an 

 aperture the size of a brick, extending from the surface of the 

 sand bottom of the furnace upwards. It is filled up with a mix- 

 ture of clay and sand. When the furnace is tapped, an opening 

 is made a little above the charge, and then cut down until a 

 small gutter is formed for the metal, which in flowing over cuts 

 deeper, making its own way to the bottom of the aperture, and 

 so emptying the furnace. 



Generally the mat or coarse metal frona the ore-furnace is 

 tapped into a large pit of water which granulates it. These pits 

 are from 6 to 8 feet deep, and from 4 to 5 feet square, into 

 which a perforated box is lowered which receives the charge of 

 metal, and which is raised by a crane or pulley, and the metal 

 removed to a yard for the next operation. This mat is termed 

 granulated coarse metal. 



Whatever modifications or improvements may have been 



