CHEMICAL SCIENCE. 233 



The per-centage of carbonic acid in the gas increases at a height of 

 10' or 11' above the nose pipe, above which point a second reaction 

 takes place between the carbon of the fuel and the carbonic acid, the 

 per-centage of the latter decreasing up to a height of 15' above the 

 tuyere, where it is 0. From this point it again increases in quantity, 

 and rapidly, for at a height of 30' it amounts to 3.5 per cent. The 

 authors ascribe this considerable increase of carbonic acid solely to 

 the decomposition of the limestone used as a flux. 



Thus after the increase of the per-centage of carbonic acid to 3 ; 5 

 in consequence of the decomposition of carbonate of lime, it a^ain 

 diminished in proportion to the increased height, until at a point from 

 37' to 39' above the tuyere it amounted to only 1.69 or 1.91 percent., 

 which may be regarded as about the quantity present in the gas be- 

 fore the decomposition of the carbonate of lime. Above this point 

 the quantity of carbonic acid increases again up to the furnace-mouth, 

 and indeed with tolerable rapidity and regularity, in consequence of 

 the reduction of peroxide of iron to protoxide by the action of car- 

 bonic oxide. 



The authors are of opinion that the carbonic acid, which is disen- 

 gaged from the limestone at a height of 27' above the tuyere and 

 again disappears almost entirely at a height of 39', reacts within this 

 space upon the ignited coke, taking up part of its carbon ; and an ex- 

 amination of the analysis confirms this view. 



Although other observers who have studied the composition of the 

 gases from the blast furnaces have not collected them at so many dif- 

 ferent heights, still their analytical results clearly indicate that in the 

 furnaces from which they took the gas, the carbonic acid derived from 

 the limestone was at least partially reduced to carbonic oxide, as at 

 Ougree. If carbonic acid is converted into carbonic oxide by pass- 

 ing over ignited carbon, the action is essentially two-fold, a combina- 

 tion of carbon and oxygen, and a decomposition of carbonic acid into 

 carbonic oxide and oxygen ; the former is accompanied by develop- 

 ment of heat, the latter by absorption of heat. The practical ques- 

 tion to be decided in the present instance is, which of these two calor- 

 ific changes preponderates ? 



Theoretically, from the experiments of Dulong, there should be a 

 considerable loss of heat. 



These considerations led the authors to employ burnt lime in work- 

 ing blast furnaces, and thus to obviate the loss of heat. The experi- 

 ment was commenced at Ougree in July, 1849. During the first few 

 days the results were unsatisfactory, the management of the furnace 

 was difficult, and the slags black and pasty. Subsequently, when tak- 

 ing into account the impurities of ordinary limestone, 63 parts of burnt 

 lime were substituted for 100 parts of limestone ; the working of the 

 furnace, until it was let out at the beginning of 1851, was continually 

 regular and good ; during these eighteen months the most satisfactory 

 results were obtained. The saving of coke and increase of produc- 

 tion were, as the experimenters anticipated, very evident ; moreover, 

 the raw iron was of better quality, and all the interior parts of the 



