418 On the Smelting of Tin Ones 
Tin ores are found in two kinds of deposits; first in veins ac- 
companied by various other minerals ; and, secondly, in alluvial 
matter in detached fragments. 
It is usual in Cornwall not to apply the word ore to the oxide 
of tin, but to distinguish it, when in that state, by the term black 
tin, in contradistinction to white tin, which appellation is applied 
to it when smelted and in the metallic. state. 
The two kinds of tin ore above mentioned are, therefore, ge- 
nerally known, by the names of mine tin and stream tin; and as 
’ they are for the,most part smelted separately, and by different 
means, and as the metal produced from them is different as to 
its purity, it may be essential to point out the causes fromm which 
this diversity seems to arise. 
Mine tin is, as I have mentioned, the produce of veins, and 
is raised with a mixture of all the substances which unusually 
accompany it. There are, not unfrequently, copper ores, py- 
rites, wolfram, micaceous iron, &c. and the separation of these, 
as also of the earthy matrix, is the object of various processes. of 
dressing, which are conducted with the greatest care, and require 
a considerable portion of labour. 
Whether, in a country where fuel for smelting is on the whole 
very cheap, it might not be economical to diminish the labour 
of dressing, and, by leaving more to be done in the furnace, re- 
duce the expense of the former operations, is a question that I 
have never submitted to a direct experiment, though I conceive 
it to be one worthy of trial. ‘The various earths may be quickly 
separated by fusion, as in the case of copper ores, which are now 
always smelted with a large mixture of the different kinds of 
spar in which they are found, all of which is easily run off by the 
fire, and the scoria or slag separated from the metallic part. 
The fusibility of tin offers a mode by which it may be separated 
from an alloy of most other metals with which it is found to exist 
in veins, as lead and zine ores are seldom mixed with it. _ This 
property is now made use of to a certain extent in refining tin, 
and might probably be taken advantage of still further, so as to 
avoid some of the charges incurred in dressing the ore. 
The metal produced from mine tin is always of inferior quality, 
owing to the mixture of other metals, and which it is probable 
could not by any mode be entirely got rid of; it is known in 
commerce by the name of common or block tin, and the quan- 
tity forms a large proportion of the whole that is brought to 
market. ' 
Stream tin is found in the lowest stratum of alluvial matter, 
in the bottoms of deep valleys, or places where a considerable de- 
posit of mud, sand, and gravel, has been made by the action of 
water ; it is often discovered occupying a thin bed incumbent on 
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