138 



place with more fuel; the bellows is worked; more ore is 

 thrown in ; and this process, being continually repeated, con- 

 stitutes the working of the blast-hearth. The slags, when 

 enough has been collected, are transferred to the slag-hearth 

 for a product of hard lead, as already described. 



" In the blast-hearth, the current of air from the bellows, 

 delivered in the centre, is made to circulate by the skill of the 

 workman, and it is the test of a good smelter that he compels 

 the blast to permeate the burning fuel equally in all parts, 

 without overheating the furnace. No sulphureous fumes issue 

 but for a short while after the fire has been roused and 

 opened, and it is during this period that the lead runs ; hence 

 the process is slow. In the reverberatory furnace the current 

 is voluminous and diffused ; the sulphureous vapours are there- 

 fore carried off abundantly, and the lead is reduced with pro- 

 portionate rapidity. Extent of exposure to the current even, 

 in some degree, compensates deficiency of heat ; and so much 

 is this the case that lead ore spread out extensively in the sun's 

 rays will, as I was assured by an eminent smelter, exhale 

 fumes of sulphur, and consume less fuel in the subsequent 

 smelting. It is in this very particular that the blast-hearth is 

 deficient : a previous preparative desulphuration, in a small 

 furnace, is practised in some places where the blast-hearth is 

 used. 



" The facility with which the slag is removed from the 

 surface of the melted matter is a great recommendation of the 

 reverberatory furnace : in the blast-hearth this can only be 

 done by drawing out the fire on the iron apron, and letting it 

 cool somewhat until the masses of slag can be seen in order to 

 be picked out. The fuel is then returned into the well, and 

 time is lost before it resumes its heat. 



" In the blast-hearth, unless there be a horizontal flue, 

 there is no small waste, by evaporation of both sulphuret of 

 lead and of lead in the metallic state. But in the reverbera- 

 tory both are detained in the horizontal flue and the high 



