I §3 On tic Affaying of Iron Ores- 



iron, as to ftrength and fufibility. In no cafe has the refuk 

 of any aflay been confidered perfect, unlefs the vitrid mafs 

 found upon the furface of the metalUc button exhibited a 

 degree of tranfparency and purity of colour little inferior to 

 flint glafs, or flightly darkened by a faint fhade of azure. In 

 fuch vitrifications, purity of colour is the furefl; proof of the 

 iion-exiftence of iron in the (late of a fufed oxyd : the fame 

 degree of pellucidity renders it eafy to deleft the fmalleft glo- 

 bule of metal which by chance may have been fufpended 

 during fufion. In all experiments where a juft affociation 

 of mixtures has been prefent to produce this peculiar fcoria, 

 the quality of the iron will be found richly carbonated, and 

 the button pofleffing a fmooth, filvery, greafy-feel furface. On 

 the other hand, experience has repeatedly fliewn, that when 

 the fcoria obtained in aflaying approached not to the co- 

 lour and purity of fine glafs, there remained a portion of the 

 iron ftill unrevived, in the ftate of a fufed oxyde, conveying 

 colour and opacity to the mafs ; that at certain degrees of 

 colour, certain degrees of opacity exifted, and proportionate 

 quantities of the metal remained diffufed in the fcoria. 

 When the colour of this was green, the quantity of metal 

 united was fmall ; but as the green deepened, and became 

 afTociated with light browns, the quantity of unrevived iron 

 was greater, and became much increafed as the fcoria af- 

 fumcd darker browns, or became totally black: in fuch \x\- 

 llances I have found it contain, upon being re-aflayed, 12 per 

 cent. The aflaying of iron ores is fufceptible of another ex- 

 treme, by which experiment is equally clogged, and wherein 

 it is very difficult to obtain an accurate rcfult. In this cafe 

 no perfect button ot metal is found, but the portion of iron 

 which the ore contained is in a vaft variety of various fized 

 globules of the richeft crude iron, intcrfperfcd in, or covering 

 the furfiice of a fcmi-vitrified opaque mafs of fcoria, of a 

 greyifli-blue, mottled, or whitifh colour. The caufes of 

 which, .and their ftriiit analogy to fimilar rcfults in the 

 liIall-fLirnacc, iljall be uiy chief objeft, to explain. 



