4/6 



NATURE 



[Sept. 12, 1889 



case of the furnace in question. Suppose 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 C, will make itself felt throughout the entire height 

 of the furnace, including, of course, the upper zone. Immediately 

 this happens, the carbon dioxide generated by the reduction of 

 the ore attacks the coke and escapes as carbonic 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 de- 

 oxidizing the ore will permit. The sensible heat in the escaping 

 gases, however, still represents a considerable loss, reduced as 

 they have been from 29,482 to 11,043 calories. 



According to estimate, it was believed that the reduction of 

 oxide of iron ought to be attended by an increase of temperature 

 — in other words, the conversion of carbonic oxide into carbonic 

 dioxide produced more heat than that absorbed by splitting up 

 oxide of iron into its constituent parts. The estimated difference 

 not being a large one, an experiment was made by substituting 

 in the furnace inert substances having about the same specific 

 heat as the ore. The results confirmed the correctness of the 

 calculation— the temperature of the escaping gases fell, and 

 rose to their normal point when the use of ore was recom- 

 menced. A more expensive experiment was subsequently made 

 in the same direction by building, at Ferry Hill, a pair of fur- 

 naces having a height of 103 feet, without any substantial benefit 

 being derived from the large additional expenditure incurred. 



It was Scheerer, I think, who first divided the blast furnace 

 into zones. The first division, beginning at the top and extend- 

 ing twelve feet downwards, was designated the preheating zone. 



the following eighteen feet downwards was distinguished as the 

 reducing zone, the next eight feet the carburizing zone, followed 

 by four feet which constituted the zone of fusion. The lowest 

 of all, having a depth of about six feet, was named the zone of 

 combustion. The author of this mapping out, as it were, of the 

 interior of the furnace, does not wish to be understood as 

 confining its various functions within the respective spaces 

 assigned to them ; on the contrary, he admits the existence of 

 considerable variations of position. My own observations, 

 however, have led me to conclusions varying considerably from 

 those adopted by Scheerer. 



The fundamental cause of these differences seems to de- 

 pend on the temperature considered as being required for 

 a commencement of the reduction of the ore. By Scheerer 

 the reducing zone is considered to require a temperature of 

 1000° to 1200° C. This change undoubtedly is not the same 

 with all kinds of ores, but my experiments were conducted 

 when using almost every variety of the mineral. Accord- 

 ing to the trials made, a mixture of one volume of carbon 

 dioxide and two volumes of carbonic oxide at a temperature of 

 410°, reirtoved 10 per cent, only of the oxygen in Cleveland ore, 

 and 37 "8 per cent, from an artificially prepared oxide. The 

 composition of the gases at the different depths, however, 

 indicates in an unmistakable manner the nature of the action 

 which is going on at any particular point. A table has been 

 prepared from actual analyses of the gases which gives the 

 quantity of oxygen present for every 1000 parts of metal 

 produced ; and to this is added the weight of carbon they 

 contained. The results vary, but the general inference to be 

 drawn from the observations made on furnaces of 80 feet, is 

 that by the time the minerals have passed through a space of 

 eight feet of the depth they have to travel, all the oxygen 

 susceptible of removal from the ore in the upper region is found 

 in the gases, the remainder being retained until it reaches the 

 zone of fusion. The same is the order of action in a somewhat 

 modified form which w as found to prevail in the case of furnaces 

 48 feet in height. 



Table III. — Showins 



the quail fit}' of Oxygen and Carbon in gases per loco parts of pig-iron produced, 

 immediately belovj charging plates is occupied by charging apparatus. 



The ^ feet 



Note. — Nos. 3 and 4 were using partially calcined limestone, hence ihe deficiency of O and C until the lower depths are reached. 



On casting the eye along the lines of figures a somewhat 

 remarkable circumstance is apparent, viz. that the quantity of 

 oxygen per loco of pig-iron gradually decreases as the gases 

 ascend, until they approach the upper region, when it commences 

 to increase. This had been the subject of observation for many 

 years without any complete explanation being given of its cause. 

 Dr. Percy, among others, bestowed some attention to the cir- 

 cumstance without arriving at any opinion satisfactory to himself. 

 It is a little extraordinary that, so far as I have seen, no notice 

 has ever been taken of the fact that the carbon in the gases 

 followed the same law. While engaged in investigating the 

 action of furnace gases on the ore a peculiarity was observed 

 previously unknown to me, viz. that large quantities of carbon 

 were deposited by the dissociation of the reducing gas, the 

 action being 2CO — COg -f C. Experimentally I ascertained 

 that .'^pongy iron, as well as oxide of iron, was capable of pro- 

 ducing the change, and that 30 per cent, of carbon dioxide, 

 mixed with the carbonic oxide, arrested the reaction, the 

 temperature at the time being 420°. Dr. C. A. Wright, who 

 subsequently became chief chemist of our Laboratory, was asked 



to continue the examination. The conclusion arrived at was 

 the impossibility of effecting the complete reduction of E^Os, 

 or of any oxide by CO. On the contrary, when metallic iron 

 known to contain no oxygen was exposed to a current of this 

 gas, carbon was deposited and oxygen absorbed. It would 

 seem, therefore, that this absorption of oxygen by the iron and 

 precipitation of carbon suffice to explain the disappearance of 

 these two elements from the gases, and that they remain in this 

 condition until the fusion of the iron, in contact with intensely 

 heated carbon, liberates the oxygen as well as that portion of the 

 carbon which is not absorbed by the metal in order to produce 

 pig-iron. 



So far, then, as the analyses given in Table III. enable us to 

 judge, instead of the upper two-thirds of a furnace being 

 required for the purposes of reduction, no material change is 

 effected after passing through eighteen feet in a modern furnace 

 of 80 feet in height. After this the composition of the gases, 

 and, therefore, of the minerals, remains pretty steady until the 

 vicinity of the tuyeres is reached, with the consequences already 

 referred to. 



