268 Mr. J. Napier on Copper Smelting. 



for all the good properties which coals have that possess all the 

 necessaiy elements within themselves ; there is not the change 

 of character, the caking and swelling, which is, we think, essen- 

 tial to the production of a continued high heat in an air-furnace. 



If coal be allowed to dry or be exposed for a long time to the 

 air, it soon loses its strength, and the subsequent addition of 

 water will not restore the loss. Coals become greatly deteriorated 

 during a long voyage owing to this cause. The best Swansea 

 coal, in its voyage to Chili or Australia, loses nearly 12 per cent, 

 of its value for smelting; a serious drawback to the smelting 

 operations abroad, as the coal being weaker is less able to burn 

 either alone or with wood. This is particularly the case with 

 some of the South Wales coals, which are known to lose their 

 strength by a few weeks^ exposure. It is also known that such 

 coal put into a ship^s hold gives out fire-damp, so that it is 

 necessary to ventilate the ship ; showing that hydrocarbons are 

 being evolved. 



The copper smelters have a peculiarity in the management of 

 their fm'naces on which much of the art depends, and is quite 

 consistent with the general laws of heat. The peculiarity is in 

 making the clinker serve the purpose of fire-bars. In lighting 

 a furnace, iron bars are used for the grate, having upon them 

 some old clinkers or pieces of brick ; the fire is continued until 

 a new clinker is formed from the ash of the coal, which should 

 be sufficient to cake by the heat of the fire, but not to fuse. As 

 this clinker accumulates and enlarges, the iron bars that Avere 

 used as a grate are removed; so that when the fire is in a good 

 condition to smelt by, the whole bottom of the furnace is com- 

 posed of a few immense clinkers supported by only two or three 

 large bars of iron fixed in such a position as will bear them. 

 From time to time they are changed as the fireman sees fit. 

 These clinkers will often be from 1 to 2 feet thick, and weigh 

 upwards of 1 cwt. ; it is on this account that attention has to be 

 paid to the nature of the ash in coal. 



In the management of these clinkers for regulating the di-aught 

 lies the secret of oeconomical smelting, and it can only be attained 

 by long experience and constant attention on the part of the 

 workmen. Some workmen can do more work with less fuel than 

 others, by a proper regulation of the draught passages, which 

 are made and kept open by means of iron bars ; breaking off 

 pieces of the clinkers in one part, closing up large holes in an- 

 other, and so on as the necessity and skill of the workman 

 suggest. 



The composition of the clinker is very regular, and may be 

 termed a silicate of iron. We have submitted a good many of 

 them to analysis; the average composition may be stated in 



