526 EEPORT — 1889. 



the appropriation of heat classified under the head of Variables will show in conse- 

 quence diminution from 73,338 to 54,643 calories. 



It may be asked whether this prolonged exposure of the ore to the reducing 

 gases could not be secured by driving the furnace at a slower speed. There is, 

 however, a point which may be regarded as one of equilibrium, at which the quan- 

 tity of cold materials charged at the top just suffices to reduce the temperature of 

 the escaping gases, as far as is possible consistent with the dimensions of the 

 furnace. If the volume of blast entering at the tuyeres is lowered one-half it 

 would mean that the materials would be exposed for twice the time to tlie hot 

 gases that they were previous to the alteration in the rate of driving. The elevation 

 in the temperature of the coke would enable its carbon to act on the carbon dioxide, 

 so that there would ensue as great a loss under the second bead of heat evolution 

 in Table I. as there is gained by a more perfect interception of the heat contained 

 in the gases. 



There is, however, another way of securing this prolonged exposure of the ore 

 to the action of the reducing gas without incurring the inconvenience just referred 

 to, viz. by increasing the dimensions of the furnace blown with cold air. When 

 this was done by raising the height from 48 to 71 feet it was found that the duty 

 performed by the coke, apart from the heat contained in the blast, was just about 

 the same as that in the hot-blast furnace. 



With regard to the position of equilibrium above referred to, it is worthy of 

 remark that, while this was reached when a furnace of 48 feet ran 100 tons "per 

 week when driven with cold air, it was not arrived at in one of similar dimensions 

 using heated air until the make was increased to about 220 tons. 



When we proceed to examine the composition and weight of the gases given 

 ofl^ by a 48-feet furnace blown with air at 485° C. it will be found that about 20 per 

 cent, of the carbon as dioxide has disappeared, due no doubt to the still excessive 

 temperature of the upper zone and too rapid a current of the reducing agent. An 

 obvious way to remedy this evil would be by an addition to the capacity of the 

 furnaces. This was done by raising them to a height of 80 feet, with a cubical space 

 three or four times greater than those of 48 feet. In such a furnace almost the full 

 theoretical quantity of carbon as dioxide has been obtained, but, while the larger 

 furnace held three or four times as much ore, &c., as the smaller one, the produc- 

 tion was only about double that of the lesser. On referring to Table II. it will be 

 seen that a further economy of 6'6 cwts. of coke has been efiected in Furnace C 

 as compared with B, due solely to an enlargement of space, for the temperature of 

 the blast was exactly the same in both. This improvement, it will also be per- 

 ceived, is due to an extension of those causes which acted so beneficially when hot 

 air was applied to B. 



If 6*6 cwts. of carbon or thereabouts is the fuU quantity per ton of iron which 

 can be found in the gases as dioxide, and if, in a furnace working under the con- 

 ditions of C, it requires 22-32 of coke to furnish this carbon and that in the carbonic 

 oxide, it is clear we cannot withdraw any coke without disturbing the position of 

 equilibrium supposed to have been established in the case of the furnace in ques- 

 tion. Suppose that into such a furnace the blast, instead of 485°, is admitted at 

 695° as happened under Column D. The additional heat, 732 calories, instead of 

 534 as in 0, will make itself felt throughout the entire height of the furnace, 

 including of course the upper zone. Immediately this happens some of the carbon 

 •dioxide generated by the reduction of the ore attacks the coke and escapes as car- 

 bonic oxide. If Table I. is examined it will be seen that almost the whole of the 

 additional heat carried into the furnace D, as compared with C, has been absorbed 

 by the disappearance of carbon dioxide, so that the net power of the coke unit in 

 both cases is practically the same. Nevertheless it will be remarked that there is 

 still a small saving of coke due to a reduced amount of blast, escaping gases, &c. 



From what has preceded it has been concluded that a furnace of 80 feet affords 

 sufficient opportunity for the gases being as fully saturated with oxygen as the nature 

 of the process of deoxidising the ore wUl permit. The sensible heat in the escaping 

 gases, however, still represents a considerable loss, reduced as it has been from 

 2!),482 to 11,043 calories. 



