Sept. 12, 1889] 



NATURE 



475 



"Column A to coke 686, limestone 75, and ore 239 cubic feet. 

 This is followed by a twofold advantage. Volume for volume, 

 ore and limestone possess double the heat-intercepting power of 

 coke, and there is 19 per cent, more ore ready to oxidize the 

 carbonic oxide passing over it at a reduced speed of 16 j)er cent, 

 than there was when using cold air. The increased efficiency of 

 the coke, due to a more perfect cooling of the gases and higher 

 oxidation of the carbonic oxide, permits its further suppression 

 until the relative spaces filled by the materials are those shown 

 •under Column B. These advantages would not of them-;elves 

 suffice to save 16 cwts. of coke or thereabouts out of 45 cwts. , 

 but the reduction in the coke consumed is followed by a diminu- 

 tion in the quantity of air used and in the weight of gases and 

 slag produced. A reference to the appropriation of heat classi- 

 fied under the head of ' ' Variables " will show in consequence 

 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 re- 

 garded as one of equilibrium, in which the cjuantity of cold 

 materials charged at the top just suffices to reduce the tempera- 

 ture of the gases, leaving it as far as is possible consistent with 

 the dimensions of the furnace. If the volume of blast entering at 

 the tiiyeresxi lowered one-half, it would mean that the materials 

 would be exposed for twice the time to the 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 head 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 ex- 

 posure of the ore to the action of the reducing gas without in- 

 curring the inconvenience just referred to, viz. by increasing the 



Table II. — Showing the appropriation of Heat and its equivalent per ion Iron. 



Appropriation of Heat per 20 of Pig-Irjs. 



Constants : — 



Reduction of Fe.203 in ore 



Reduction of metalloids in pig 



Dissociation of CO(2CO = C -f COj) 

 Fusion of pig-iron 



Constant calories per 20 of pig 



Coke consumed per 20 of pig. 



Variables : — 



cwts. 



Evaporation of water in coke 



Decomposition of water in blast 



Expulsion of COo in limestone 



Reduction of CO, in limestone to CO 



Fusion of slag 



Carried off in escaping gases 



Heat in tuyere water at hot-blast furnaces, "> 

 loss from walls, &c / 



Variables for 20 of pig 



A— Blast qo C. 



Calories. Cwts. coke 



33,108 



4.174 

 1,440 

 6,600 



45.322 



630 



5,420 



6,660 



6,912 



18,590 



29,482 



73,388 



B— Blast 485° C. C— Blast 485° C. 



Calories. Cwts. coke Calories. Cwts. coke 



12-550 i 33,108 

 1-5821 4,174 

 0-546 1,440 



2-501 



17-179 



0-239 



2-055 

 2-526 

 2-620 



7-045 

 11-178 



6,600 



45,322 



5,694 2-158 



411 



3,348 



5,920 



6,144 



17,325 



18,486 



7,011 



— 58,645 



Variables for coke for 20 of pig cwts. 



Sum of Constants and Variables : — 



Calories for 20 of pig-iron 118,710 



Cwts. of coke for 20 of pig-iron I — 



27-821 



45-000 



103,967 



9-209 

 1-161 

 0-400 

 1-836 



33,108 



4,174 

 1,440 

 6,600 



D— Blast 6950 C. 



Calories. iCwts. coke 



7*905 33,108 



0-996 , 4,174 



0-344 j 1,440 



1-576 , 6,600 



45,322 I — 



45.322 



1 2 '606 : — 



10-821 



0*114 

 0-931 

 1-647 

 1-709 

 4-819 

 5'i44 



312 



2,720 



5,054 



5,248 



16,720 



11,043 



I 950 7,057 



0-074 

 0-649 

 1-207 

 I "254 

 3*993 

 2-636 



1-686 



298 

 2,408 

 4,070 

 4,099 



15,565 

 8,906 



9,389 



48,154 



— \ 44,735 



16-314 — 



— 93,476 

 28-92 — 



11-499 



— , 90,057 

 22-32 — 



7-808 

 0-984 

 0-340 

 I '557 



0-070 

 0-568 

 0-961 

 0-962 



3*673 

 2-101 



2-616 



10-551 



21-24 



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 fur- 

 nace 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 off 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. , the production 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 effected in Fur- 

 nace 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 perceived, 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 full quantity per 

 ton of iron which can be found in the gases as dioxide, and if, 

 in a furnace working under the conditions 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 



