Mr. J. Napier on Copper Smelting. 351 



a fm-nace is built, a fire is kept in it until it is considered to be 

 sufficiently di-y and annealed to be fit for working. The bo';tom 

 is made as follows : — Sand is laid upon the brick bottom to the 

 depth of about 18 inches, which is kept at a red heat for about 

 24 hours, when a little slag is laid on the top of the sand ; the 

 furnace doors are all closed, and the heat increased to the melt- 

 ing-point : the slag fuses over the surface, penetrating into and 

 combining with the sand to about the depth of an inch j when 

 this is accomplished, the heat of the furnace is gradually lowered. 

 The whole surface of the sand bottom has now become one piece 

 of hard glass, adhering firmly to the side walls, forming a com- 

 plete shallow vessel. This forms what is termed the true or 

 lower bottom of the furnace. Upon the top of this bottom is 

 put a second layer of sand about 6 inches deep, which is treated 

 in the same manner, and is termed the false or upper bottom. 

 This upper bottom is of great practical value, as the bottom, 

 exposed to cold currents, is always liable to crack ; or it may be 

 separated slightly from the side walls, and allow the fluid to 

 pass through and under ; but it only passes to the surface of the 

 lower bottom, which is not affected by the crack, flows over it, 

 and raises the upper in pieces, which is easily withdi-awn, and a 

 new upi^er bottom put in. Were it not for this provision, and 

 an opening or crack taking place in the main bottom, or a piece 

 of it breaking and coming up, the renewing of a bottom would 

 be a most serious matter, and the copper constantly penetrating 

 would be a source of great loss. As it is, there is a constant 

 penetration of the melted juatter, more or less according to the 

 nature of the sand, the care of the workman, and the condition 

 of the copper in process of manufacture. The nearer it ap- 

 proaches the condition of metal, the greater the liability to pe- 

 netrate. Some bottoms of refining and roastiug-furnaces have 

 been often known to contain from twenty to thirty tons of copper ; 

 indeed, so great is the amount of capital absorbed in this way, 

 that the average value of each furnace used for fusing may be 

 reckoned at i;500 after one year's working. 



Formerly, instead of the fui-nace being built upon ^n arch, as 

 above described, it was one solid mass of brickwork, in which 

 case the penetration of metal was much greater, as the free 

 current of air passing through the arch keeps the bottom cool 

 and prevents the metal from running through. 



A plan for lessening the quantity of copper penetrating into 

 the bottom was proposed a few years ago, and we behevc is the 

 subject of a patent. Instead of an arch of bricks, the side ,valls 

 are started from the ground, and the sand bottom is supported 

 by iron plates laid across and resting upon the side walls at the 

 proper height. Trials with these iron bottom supports did lessen 

 the penetration a little, but the great liabihty of the iron plate 



