422 On the Smelting of Tin Ores y 
smelting is finished, or in a similar one, which may be reserved 
for the purpose. : 
All the processes for refining metals in the fire must be per- 
formed by taking advantage of some property in which the metal 
operated on may differ from those with which it is alloyed, and 
which it is intended to separate from it. These differences may 
consist in the facility or difficulty of oxidation, in their tendeney 
to volatilize, in the temperature required for fusion, or in their 
relative specific gravities. 
Upon an attention to the two latter circumstances is founded 
the operation for refining tin, The substances which are most 
‘to be suspected in the produce of the first melting, and which it 
is desirable to separate, will probably be iron, copper, arsenic, 
tungsten from the wolfram, which the miners call mock-lead, 
and a portion of undecomposed oxides, sulphurets, or arseniates, 
and of some earthy matter or slag. 
The furnace for refining is raised but to a very moderate de- 
gree of heat, and the plates of tin being placed in it are suffered 
to melt very gradually, and the metal flows from the furnace at 
once into the kettle, which is now kept hot by a small fire placed 
beneath it. The more infusible substances will now be left in 
the furnace, and a further purification of the tin is obtained by 
agitating it in the kettle for some time by an operation which 
they call ¢ossimg: this is performed by a man with a ladle, who 
continues for some time to take up some of the melted metal, 
and pour it back into the kettle from such a height as to stir up 
the whole mass and put every part into motion. 
When this is discontinued, the surface is carefully skimmed, 
and the impurities thrown up are removed ; these consist of such 
matters as are lighter than the tin, but which are suspended in 
it, and, being disengaged by the motion, find their way to the 
top. In general, the metal is at once laded into the moulds, 
after the tossing and skimming are completed; but the produce of 
impure and irony ores may yet require that the tin be divided as 
much as possible from the mixture which may yet remain. This 
may be effected in a great degree by keeping the mass in the 
kettle in a melted state, by which the parts which are heavier 
than the tin will sink to the bottom, and by leaving a proper 
portion behind, the tin will be materially improved. 
The last operation is that of pouring the metal into moulds, 
which are usually formed of granite, and which are of such a size 
as to make it into pieces of somewhat more than three hundred 
weight each. These are called blocks, and are sent, according 
to the provisions of the Stannary laws, to be coined by the Duchy 
Officers ; and it then comes to market under the name of Block 
Tin, or acertain part which has been treated with more than 
common care is called Refined Tin. The 
