388 On the Affaying of Ores hy Fujto^i 



able ftate. In this procefs the quantity of malleable iron ob-: 

 tained is ftill lefs than in the two former : the furface of the. 

 metal being expofed by the removal of the fcoria, oxydation 

 takes immediate effeft; and whilft malleability is pervading 

 the under furface of the metallic button, the upper one be- 

 comes reduced to a blackiOi blue oxyde. In this operation 

 a ftriking proof is afforded of the great affinity which oxygen 

 has, in high temperatures, to caloric. Were the furface of 

 fuch highly oxygenated crude iron expofed, while fluid, to 

 atmofpheric air, at an ordinary medium, for i-6th of the 

 time, its whole metallic properties would* be completely de- 

 ftroyed : in the prefent inftance nearly one-half of the meta! 

 is preferved, although its furface is expofed to the aftion of 

 a violent current of gas, ignited to the higheft pitch of white- 

 nefs *. In the proper allay of this ore I have found all the 



varieties 



* I have frequently obfcrvcd, in exjieriments whh pretty deep crucibles, 

 where the moft violent heats were excited, and where the fluid metal had 

 afTnrtied a \vhitifli-b!ue colour fomewhat inclining to azure, that the quan- 

 tity of oxyde formed was imperceptible, and never vifible while the heat 

 was continued of equal intenfity ; when this agent became lefs urgent, the 

 furface of the metal became o.xydated as ufual. When a regulus of crude 

 hon thus expofed was wiftied to be obtained free from oxydation, a little 

 dry charcoal was introduced into the crucible fo as to cover the regulus ; 

 tliis prevented the a^ion of the air from taking effedl while cooling, and 

 pfeferved rhe button fmootli. During fuch expofures, when no oxyde was 

 produced, I have noted a lofs of metallic parts equal to 5.7, or \o per cent. 

 when the fpace of time did not exceed one hour. Among feveral conjec- 

 tures refpe£ting the caufe of this deficiency in weight, and real abftraftion o£ 

 metal, the two followhig have with me moft weight, ift, Either the metal 

 deflagrates in fmall particles, which are thrown out of the crucible in fpar- 

 kles, made invifiblc by the tranfcendcnt brightnefs of the furrounding heat: 

 Or, 2d, that in confequence of the fluid metal being expofed to fuch a great 

 degree of heat, in contaft with oxygenous gas, part of it becomes acidified, 

 and forms the ferric acid. The truth of this laft fuppofition will not eafily 

 be afcerfained, fince it will be difficult to conftruft an apparatus capable of 

 receiving or containing it, fhould it prove to be an elaftic fluid : it is, how- 

 ever, confonant to the doftrines of the new theory, and the poffibility of 

 the exiftence of the ferric acid is by no means excluded. The diffipation of 

 ' ' carbon 



