Oft the Component Parts of Iron-Jloites , 243 



ft ■will no doubt be obferved, that the increafe of weight 

 in thefe ftatements tally not with the fums formerly given : 

 the amounts there adduced are refults from iron-ftones which 

 Had been previously deprived of moft of their oxygen; but 

 in thefe, the extra quantity of oxygen taken up by the 

 ftone is only given, forming an aggregate, with the original 

 exifting quantity, as fhall hereafter be mown, nearly cor- 

 refponding to the fums firfl given. 



From thefe experiments, fingled out to convey a juft idea 

 of the changes to which iron-ftone may be fubjected, it be- 

 comes obvious, that all the varieties of iron-ftone are ca* 

 pable of decompofing atmofpheric air at a certain tempe- 

 rature, and of fixing a portion of its oxygen, whereby weio-ht 

 is gained, by each, nearly equal to i-8th of its original 

 quantity. 



It muft alfo from this appear obvious, that the burnincr 

 of iron-ftone is an operation — though hitherto conducted by 

 chance, expofed to all weathers— of the greateft nicetv, and 

 confequence to the certain and economical manufacture of 

 caft-iron ; wherein a fm'all addition of fuel, by excitino- a 

 high temperature, expofes the iron to the combination of a 

 hurtful principle, in quantity (as will hereafter be fhown) 

 almoft equal to what the metal was originally precipitated in. 

 The extra proportion of fuel, therefore, requifite under cir- 

 cumftances where a fevere mode of torrefaction is either 

 univerfally adopted, or where it is frequently the refult of in- 

 attention and want of null, though as yet unafcertained 

 upon a large fcale, raufl be very confiderable. 



I look upon it therefore to be a great defideratum in the 

 preparation of iron-ftone, to contrive a mode which woul(3 

 unite certainty and economy ; a mode which would either 

 de-oxygenate the ore uncxpofed to external air, or which 

 would dilfipate its volatile mixtures expofed to air, with a 

 degree of certainty which, with a fmall fhare of attention, 

 would preclude the poftibility of the metal attracting more 

 oxygen. 



R2 la 



