[ 307 1 
pofed to a llrong fire, in which they are m^de c|Uit^ 
clear, and colourlefs. Befides, if this glafs, tinged 
blue with the copper, is again melted with more 
of this metal, it becomes of a good green colour, 
which for a long time keeps unchanged in the fires 
SECT. XLV. 
The iron ores, when pure, can never be melted » 
by themfelves, through the means of the blow- 
pipe alone, nor do they yield their metal, when 
melted with fluxes, becaufe they require too ftrong a 
heat to be brought into fufion ; and, as both the ore 
and the metal itfelf very foon lofe their phlogifton 
in the fire, and cannot be fnpplied with a fufEcient 
quantity from the charcoal, fo likewife they are 
very foon calcined in the fire. This eafy calci- 
nation is alfo the reafon why the fluxes, for in- 
fiance borax, readily fcorify this ore, and 
even the metal itfelf. The iron lofes its phlo- 
gifton in the fire fooner than the copper, it is there- 
fore eafier fcorified ; and this is the principle on 
which the experiment mentioned in Sed. xlii. h 
founded. 
SECT. XLVL 
The iron is, however, difcovered vfi thou t milch 
difficulty, although it were mixed but in a very 
fmall quantity with heterogeneous bodies. The 
ore, or thofe bodies v/hich contain any large 
quantity of the metal, are all at'traded by the load- 
ftone, fome without any previous calcination, and 
others not till after having being roafted. When 
a clay is mixed with a little iron^ it commonly 
melts by itfelf in the Are ; but, if this metal is 
contained in a limeilone, it does not promote the 
X 2 fufion^ 
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