in Cornwall and Devonshire. 
361 
admits of calcination, by which the specific gravity of the sulphurets 
or arseniats with which it is mixed, may be lessened, and a mode 
obtained of rendering them more separable. 
3d. That the weight of Tin Ore being greater than most others, 
it is less liable to waste in the processes of washing, and therefore 
may be dressed so as to be nearly clean from all substances not 
actually adhering to it. 
From the first of these peculiarities it follows, that all tin mines 
must be furnished with stamping-mills of sufficient power to bruise 
down the ores raised, which is generally done so as to produce a 
minute division of the whole, and on this account, formerly, the 
quantity and fall of water that could be applied to this purpose 
usually limited the quantity of ore that could be returned from a 
mine, or the whole was frequently carried to some spot favorable 
to the erection of water-wheels to be applied to this purpose. 
Within a few years steam power has been applied to stamping- 
mills, and has tended to increase the supply of tin ores. Engines 
for this purpose, of considerable power, are working with great 
effect at two of the largest tin mines in Cornwall, Wheal Vor and 
Great Huas ; from which are now arising abundant returns of the 
metal, and where formerly it would have been impossible to have 
produced it. 
The state of division, or the size, as the tin dressers call it, is 
regulated by a plate of iron pierced with small holes, through 
which the whole passes from the stamping-mill, being washed 
through by a rapid stream of water conducted upon it for the 
purpose. This is a point of great importance, and is regulated by 
the state of dissemination in which every ore is found. 
It is not the intention of this memoir to detail the processes of 
dressing which are common to most ores, and therefore it may be 
2 z 2 
