C 95 3 
As to the other point of the iron bars impregnating 
the copper, in the manner defcribed in my letter, I 
examined it with the utmoff attention, and was ’an 
eye-witnefs to it in all its progrefs, and fo are thou- 
fands. I faw the mafons laying a chain of new ffone 
troughs, or pits, for the copper-water to run through. 
I faw men laying the iron bars on wooden rafters in 
thefe troughs. I had the iron bars lifted up out of 
fome pits, where they had lain in the water from one 
to eight months, and faw them incruffed with the 
coppei 1 uff j and corroded to thin plates, in propor- 
tion to the time they had lain in the water. I faw 
fome of the pits emptied, wherein the iron bars were 
wholly diffolved ; and the labourers throwing up 
with fhovels the copper, which lay on the flags in 
the bottom of the pit, like mud : and out of one of 
the heaps of copper-mud, which I faw thrown up, 
I took that very parcel of copper duff, which I lent 
to your lordfhip. It was like mud, as it lay wet in 
the heap; but became duff, as it dried. I alfo 
faw feveral pieces of copper, which I was informed 
were made out of this kind of copper- mud. And 
Dr. Dumainbray, in his philofophical lectures in 
Dublin, fhew’d to us a plate of pure copper made 
in this manner ; which led me to go to the mines, 
and there make this minute inquiry. 
I muff take notice of one improvement, which I 
omitted in my letter. To prevent any dirt or mud : 
from being carried out of the mines, by the ffreams, . 
which are let into the pits, where the iron bars ar.e de- 
pofited, the flream, as it iffues out of the level, is col- 
lected into a large deep bafon, where all the dirt lub- 
fides 5 
