C 60 1 
glaffy fubftance, forming, as it were, a covering over 
the metal, which, by its gravity, naturally links to the 
bottom; this the workmen call cinder. Now the 
want of this matter rendering the operation too tedi- 
ous, I find they had recourle either to this cinder 
brought from other iron works, or to a quantity of 
the bogmine, which, I doubt not, would abundantly 
furnifh matter for cinder. If they had ufed only the 
firff, and that properly chofen, it might very probably 
have been of fome fervico, without doing any material 
injury to the metal ; but if the bog mine is ufed, 
though the fervice might be apparently more, yet 
in all likelihood the injury would be infinitely great, 
and I am inclined to believe that fomething of this 
kind occafioned the difference obferved between the 
two barrs above mentiond, viz. that the one might 
have been reduced by the help of more pure materials, 
and the other by the afiiftance of their bogmine, 
whofe conftituent parts abounding with many impu- 
rities, fome of which, by mixing with the metal, 
may have occafioned the defeats above complained 
of, and which required fo fev-ere an operation both of 
the fire and hammer to feparate from it. I am there- 
fore of opinion, that as the profecution of this ufeful 
difcovery deferves the greateft encouragement, if the 
Society of arts and manufactures fhould take it under 
their patronage, the premium they may think proper 
to propofe fhould rather be given to the perfon who 
fhall produce the pureft metal, than to him who fhall 
produce the greateft quantity* for otherwife, I am 
afraid, we fhall be deprived of what I fhould efleem 
the moft valuable part of this difcovery, 1 mean the 
obtaining 
