Mr. H. L. Pattinson on the Smelting of Lead Ore, fyc. 173 



on an average 20oz. of Silver per ton ; it is generally worked up at the 

 end of the year, by being reduced into Lead and again refined. As the 

 cake of Silver becomes nearly pure, it is most essential to keep it con- 

 stantly in fusion, for, if once suffered to solidify, it is very difficult to 

 excite a sufficient heat to melt it again. The fire is therefore urged 

 with great violence, until at length the whole of the Lead being oxydized, 

 the formation of Litharge ceases, and the mass of melted Silver ap- 

 pears pure and beautifully resplendent. At this stage, it sometimes 

 happens that drops of melted slag from the furnace roof fall down up- 

 on the fluid Silver, in which case they are carefully brought to the edge 

 of the melted metal, and raked off upon the naked part of the test. 

 The blast from the bellows is now stopped, the fire is slacked, and the 

 Silver suffered to cool ; which it does, very gradually, first at the sur- 

 face, forming a solid crust over, a portion remaining fluid below. 

 When the temperature has fallen sufficiently, this also becomes solid, 

 and in the act of doing so, a large quantity of nearly pure oxygen gas 

 is expelled from it, and at the same instant its particles expand consi- 

 derably, so as to break the crust already formed, and force out a por- 

 tion of Silver, to the height of three or four inches above the rest of 

 the cake. Occasionally particles of melted Silver are projected out of 

 this mass, to a distance over the naked part of the test, and the sides 

 of the furnace, by which a loss of the precious metal is sometimes sus- 

 tained. After having cooled sufficiently, the cake of Silver is removed 

 from the furnace along with the test, from which it is then separated 

 without difficulty ; and if any slag or portions of the test are found to 

 adhere to it, they are cleaned off, and it is ready for sale. 



During the working of each test it gradually absorbs Litharge until 

 saturated, and the portion thus combined, is sufficient to pay the cost 

 of extraction. For this purpose, the old tests are broken to pieces, and 

 smelted in the slag hearth, mixed with a portion of black slag, in order 

 to render the bone ashes more fusible ; the black slag used being run 

 into lumps for the purpose, and not granulated in the ordinary way. 

 The produce of this fusion is a description of lead called test-bottom 

 Lead, which is very hard, and of inferior quality. 



