On the Primary Ores of Iron. 35? 



Accuftomed to apply the ores by weight, a determinate 

 quantity is frequently introduced into the furnace without 

 adverting to its fuperior richnefs in iron, and the confequent 

 extra proportion of fuel neceflary to take up its relative pro- 

 portion of oxygen. The nature and confequences of this 

 will he better underftood by the following example ; firft 

 premifing, that the quantity of oxygen — which is the great 

 evil to be got rid of — exifts in a juft proportion to the quan- 

 tity of iron. Suppofe then a blaft or fmelting furnace, 

 burdened in the following manner as to coaksand iron-ftone: 

 Coaks 400 lb. — Torrefied iron-ftone of various qualities 

 420 = 820 : let this quantity be fuppofedto yield in the blaft 

 furnace 40 per cent, then each charge will yield 168 lb. 

 Let it alfo be fuppofed that this proportion of materials af- 

 forded fuper-carbonated iron ; in this cafe there was prefent, 

 not only a fufheient quantity of carbon to take up the oxy- 

 gen contained in the ore, but fuch an abundance as to unite 

 with the iron and to form plumbago. Should it be wiflied 

 to reduce the quality, or to increafe the quantity of the pier- 

 iron, by rendering it lefs carbonated ; and ftiould this be 

 ■effected by adding to the above mixture a fmall box of 

 Cumberland ore containing 60 lb., then a portion of iron, 

 with its accompanying oxygen, (fuppofing the ore to yield in 

 the blaft furnace 55 per cent.) would be thrown into the 

 furnace equal to 33 lbs.; and the total produce of iron, per 

 charge, would be 168+33 = 201 pounds, making a fum 

 nearly equal to f of the original quantity. This portion 

 would of courfe require f of additional fuel to preferve the 

 original quality of the metal : it is even prefumable that 

 the proportion of coaks increafes in a greater ratio, owing to 

 the fpecdy defcent of the ore through the furnace : this in- 

 ereafe may be fairly eftimated as 5 to 8. The quantity of 

 fuel being now too little to take up all the oxygen, part of the 

 metal remains unre\ived, and flows out, minutely divided, 

 and interfperfed through the fcoria, in the (late of an oxvdc ; 

 the fepuated metal, deprived of its original portion of ihar- 

 A a 3 coal, 



