t 307 3 



pofed to a ftrong fire, in which they are made quit& 

 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 fire* 



SECT. XLV, 



The iron ores, when pure, can never be melted 

 by themielves, 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 fupplied with a fufficient 

 quantity from the charcoal, fo likewife they are 

 very foon calcined in the fire. This eafy calci- 

 nation is alio the reafon why- the fluxes, for in- 

 ftance 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- 

 tore eafier fcorified •, and this is the principle on 

 which the experiment mentioned in Seel. xlii. is 

 founded. 



SECT. XLVL 



The iron is, however, difcovered without much 

 difficulty, although it were mixed but in a very 

 final) quantity with heterogeneous bodies. The 

 ore, or thofe bodies which contain any large 

 quantity of the metal, are all attracted by the load- 

 ftone, fome without any previous calcination, and 



iers not till after having being roafted. Y/hen 

 a clay is mixed with a little iron, it commonly 

 melts by itfelf in the fire ; but, if this metal is 

 contained in a limeftone, it does not promote the 



X 2 fufion, 



