353 Mr. J. Nai)ier on Copper Smelting. 



to burn through rendered them useless. We have seen one in a 

 refining furnace give way in a few weeks, and a charge of seven 

 tons of copper run into the ash-pit, leaving no remedy but to pull 

 down the furnace to the ground. 



We have tried bottoms constructed with bricks and tiles made of 

 clay and plumbago, and these grooved and tongued to fit into each 

 other, as the deals of a floor, and cemented together by the same 

 materials as they were made of. Such bottoms were perfectly im- 

 pervious to copper ; but they were liable, with the slightest inat- 

 tention, to open at the joints and allow the copper to pass under 

 and raise the whole. We have also laid the whole bottom with 

 tlay and graphite, baking it carefully to make one solid piece. 

 Such bottoms we have had in work for five weeks without any 

 copper penetrating ; but although made about three inches thick, 

 it was worn through in that time, and required as many days to 

 renew as a sand bottom requires hours, and which if the sand 

 be good will last longer. This loss of time is of so much im- 

 portance where there are forty or fifty furnaces, as to leave no 

 doubt which to adopt. When a sand bottom is to be renewed, 

 or when it breaks, the fire is kept up for some time, then a hole 

 is made in the side of the furnace under the top bottom, when 

 the copper flows out, where the two bottoms join. The heat is 

 continued until as much of the melted matters sweats out as 

 possible, leaving the sand less tenacious ; it is then drawn out 

 by iron rakes or rabbles. The old bottoms are broken up and 

 crushed fine, and put into the fusing-furnace with the ore. These 

 old bottoms, with old lining bricks and clay, are termed cobbing, 

 a term we may have occasion to use again. 



From what has been said respecting the necessity of obtaining 

 ffood bricks and clay, it will be obvious that the same care must 

 apply to the selection of the sand for bottoms. If the sand be 

 too coarse, the bottom will be porous j if too fine, there is great 

 liability to crack and break up ; should it contain matters that 

 make it fusible, it soon melts away and mixes with the slags ; 

 the sand should therefore be as pure sihca as possible. The 

 proper physical qualities of sand best suited for bottoms are easily 

 ascertained by a little experience and observation ; but the che- 

 mical character, upon which a great deal depends, must be found 

 by experiment. The following analyses of a few sands, either in 

 use or tried for bottoms, will serve as data to judge of the qua- 

 lities of a sand. 



From Coadyall, Wales : — 



Silica 



Peroxide of iron . . 



Alumina .... 



Lime 



99-3 



