OF CORNWALL. 207 
|jrefent that of tin, it being computed " that, for fourteen years laft 
paft, the copper of this county has produced cafh, one year with 
the other, to the amount of one hundred and iixty thoufand pounds. 
This is a happy addition made within thefe forty or fifty years 
to the employ and revenue of this county ; and what the Cornifh 
gentlemen have now to confider is, whether both may not eafily be 
ftill improved. 
The water, in which they wafh their copper ore, has been sect. xiv. 
lately experienced by an ingenious foreigner 0 to make as good blue 
vitriol as any in the world, which appears from the vitriol manufacture ''^2 
lately carried on at Reddruth ; but there is ftill another, and more wall , fuggelted 
profitable ufe to be made of the fame. The water which comes Miners. 0 ' 
from the bottom of the mine, is now buffered to run off in wafte 
through the adit, whereas it is fo ftrongly impregnated with copper, 
that if, together with the water in which they griddle , jig, (lamp , 
and huddle the ore, it was collected carefully, and detained in pro- 
per receptacles and pits, old pieces of iron might be immerfed in 
thefe pits to great advantage, and thereby a quantity of malleable 
copper might be obtained without hazard or attendance, or other 
coft than that of the molt ufelefs old iron. When the water is 
ftrongly impregnated, the exchange is ulually quick, and performed 
in fourteen days ; but if a much larger fpace of time was required, the 
demurrage will be well requited. The experiment has been tried by 
W. Lemon, Efq; of Truro, and with fuccefs : I have alfo a lpecimen 
of ore precipitated in the copper-mine of Trewan in St. Agnes, and 
there is fcarce any copper-mine but will have the fame effe<ft ; and 
the gain may be eftimated in feme meafure by a calculation made 
at the copper-mines of Arklow in Ireland, where “ one ton of iron- 
bars immerfed in the adit in twelve months time produces one ton 
and nineteen hundred and a half weight of copper-mud, or dull ; 
now, each ton weight of mud, when melted, produced fixteen 
hundred weight of the pureft copper, felling at ten pounds per ton 
more than the copper made of the ore p . In thefe mines the pro- 
prietors had at one time five hundred tons of iron, and might with 
proportionable advantage have laid in as many thoufands. The 
fofteft iron is beft ; the pits ten feet long, four wide, and eight deep ; 
the fides faced up with ftone and lime, with wooden beams acrofs 
the pits to reft the iron bars upon : chains of thefe pits are conti- 
nued along the ftream as far as the dire&ors pleafe, for the water 
never abates its quality V’ It is not every ftream which comes from 
» 
n Letter from William Lemon, Efq; to the au- p Philofophical T ranfactions for I 75 2 > P a S e 
thor, January 12, 1758. 502. 
0 Mr. Rouby of Plymouth. 9 Ibid. 
a copper 
