OF CORNWALL. 321 
ores were mofl: ufually walked. This water, ftrongly impregnated 
with the vitriolic particles which thefe ores abound with, was firft 
put into a large lead ciftern, where it refted till the fediment fub- 
fided, and the water was clear : it was then conveyed into a boiler 
of the fame metal, where it was kept conftantly boiling by a gentle 
fire for feven or eight days, and when they found it ready, that is, 
by evaporation reduced to a proper pellicle (which they diftinguifh 
by the colour) it was drawn off through a cock at the bottom of 
the boiler, and fet in leaden cifterns to cryftallize, the falts {hoot- 
ing round the fides of the veffel, and fixing upon pieces of timber 
thrown in on purpofe to colled: them. The time required for cry- 
ftaliization was either three or five days, according to the weaker 
or ftronger impregnation of the water ; about eight tons of which, 
well impregnated with the vitriolic quality, would give a ton of 
blue, fine vitriol, each ton worth eighty pounds, or near it, and 
the expence of making each ton not exceeding fifty pounds, as I 
have been informed. The materials for making this vitriol are fo 
cheap, and in fuch plenty, that the whole kingdom might be fup- 
plied with this fait from Cornwall alone, if neceffary. 
But of all arts, that which concerns moft nearly the gentlemen Art of aflay- 
of this county to cultivate, is that of affaying metals, an art which inS 
fhould be much more generally known and pradifed, than it is at 
prefent, in a county fo fertile in foflils. 
The value of tin-ore is well known, of lead not fo thoroughly, 
and the agents of the copper-companies are almoft the only perfons 
who afiay copper-ore : here therefore ends all our docimaftic 
knowledge, and we are not only obliged to take the word of the 
buyer (which may naturally be fuppofed fomewhat in favour of 
himfelf ) as to our lead and copper, but our cobalt, bifmuth, fpel- 
tre, manganefe, and the like, lie utterly unknown and negleded : 
Great pity it is that fo many gentlemen of fortune and inheritance 
as the mine-diftrids in this county may boaft of, can find no link 
to afiociate themfelves in fo ufeful a defign as that of employing a 
proper perfon, and ereding one or more affay-ofhces whereto every 
man at a fmall expence might have accefs for information, as to 
the value of his ore, and the nature of any new foffil which 
occurs. _ 
In fome counties publick premiums, exhibited at the expence or 
a fubfcribing fociety, have had the defired efied in furthering im- 
provements of publick benefit; perhaps fomething of the fame 
kind would be of ufe in this county, and greatly promote the 
inclofing commons, planting fruit and foreft-trees, making the 
mofl: and beft-finifhed highways, improving the powers, or retrench- 
ing the expence of any hydraulic engine, difcovering new and more 
D ^ jq effedual 
