976 



IRON 



15 and 30 feet is referred by these chemists to the decomposition of the limestone used 

 as a flux : and its gradual diminution above this point indicates a reaction of consi- 

 derable importance, that, namely, of the carbonic acid upon the ignited coke carbon 

 being taken up and carbonic oxide formed. Now, the quantity of carbon taken up by 

 275 parts of carbonic acid to convert it into carbonic oxide, amounts to 75 parts, and 

 as in the furnace experimented with, 20,000 kilogrammes of limestone, containing 

 about 8,000 kilogrammes of carbonic acid were consumed every 24 hours, a loss 

 of fuel equivalent to 2,173 kilogrammes of carbon was daily occasioned by the con- 

 version of this carbonic acid into carbonic oxide, and this may be considered equi- 

 valent to 2,500 kilogrammes of coke with 11 per cent, of ash. The heat absorbed by 

 the conversion of the carbonic acid of the limestone into a gaseous state is found 

 by calculation, taking the specific heat of carbonic acid at 0'22, and the heat ing 

 power of coke at 600, to be equivalent to that developed by the combustion of 

 322 kilogrammes of coke. Now it was demonstrated by Dulong that the quantity 

 of heat disengaged in the conversion of carbon into carbonic oxide is much less 

 than that disengaged in the conversion of carbonic oxide into carbonic acid, although 

 the same quantity of oxygen is required in both cases. The conversion of carbonic 

 acid into carbonic oxide by passing over ignited carbon is essentially a twofold 

 action : a combination of carbon with oxygen, and a decomposition of carbonic acid 

 into carbonic oxide and oxygen ; the former is accompanied by development, the 

 latter by absorption of heat ; the latter preponderates to such an extent as to indicate 

 a loss of temperature equivalent to the heat developed by the combustion of 1,609 

 kilogrammes of coke. 



These considerations led the authors to employ burnt lime in working blast-furnaces, 

 and thus to obviate the loss of heat : the results were not at first satisfactory, the 

 management of the furnace being very difficult, and the slags black and pasty ; but 

 subsequently the working was regular and good, and the saving of coke and the in- 

 crease of production are stated to have been very evident ; moreover, the raw iron was 

 of better quality, and all the interior parts of the furnace, especially the tymp-stone, 

 remained in a much better state of preservation than when limestone was used. The 

 following table shows the quantity of coke consumed for every 100 kilogrammes of 

 raw iron, and the production during six months. The figures in the first column refer 

 to the furnace, in which limestone alone was used ; the second column to the same 

 furnace, in which burnt lime alone was used ; and the third column to the furnace 

 in which limestone was used for three months, and burnt lime for the next throe 

 months : 



The very regular and uniform results given in this table, show that by the use of 

 burnt lime, the consumption of coke for every 100 kilogrammes of raw iron was 

 reduced by 14 to 15| kilogrammes, while at the same time the production of iron 

 increased, within a certain period, as much as 22 to 24 per cent. 



Hitherto the opinion of metallurgists, with regard to the use of burnt lime*, was 

 rather unfavourable than otherwise, but since the above experiments were made (at 

 Ougree), it has been employed with good results in England and Wales, and as much 



