18J6.] 



Tm<: CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



115 



»arietjr of ore. They are especially applicable to the hemetites and such 

 nrei as are either naturally porous or become so in their passage through the 

 fire-room of the furnace, thus increasing the surface of contact exposed to 

 the action of the reducing agent (carbonic oxide), so that when it has reached 

 the boshes the reduction is nearly complete. 



The specular, magnetic, and siliceous ores, are reduced with much more 

 difficulty ; most of the ore, in these cases, reaching the boshes but slightly 

 titered.they being principally dependent upon the direct action of coal for 

 their reduction. This circumstance largely increases the consumption of 

 •oal when any of these ores are employed; and the amount of caloric made 

 latent, in consequence of the reduction requiring the direct action of the coal, 

 ia very great; whereas in the reduction of the ore by carbonic oxide no heat 

 becomes latent, for the heat rendered latent by the oxygen of the ore be- 

 coming gaseous, is compensated by the sensible heat produced by the com- 

 bination of the carbonic oxide with the oxygen. Where the reduction is 

 produced by the carbon, with the formation of carbonic oxide, 1598 unities 

 of heat are made sensible, while C216 are rendered latent, giving a ditference 

 of absolute loss of 4618. 



It should be the object of the metallurgist to reduce as much of the iron 

 at possible by the oxide of carbon. Magnetic, siliceous, and other hard 

 ores, should be reduced to smaller fragments than those softer and more 

 easily managed. Were it possible to reduce them to ponder without the 

 danger of choking the furnace, it would be all the better, as the great object 

 is to have a large extent of surface exposed to the carbonic oxide. The dif- 

 fercTit capacity of different ores for reduction shows the necessity of having 

 furnaces of different dimensions for them respectively. 



The matter which covers the melted metal in the crucitde, and that which 

 adheres to the interior of the hearth, contains silicate of iron and charcoal 

 in a pasty state, and there is consequently a constant reduction of the oxide 

 of iron, which gives rise to carbonic oxide; this gas bubbles through the 

 Blag, which, if drawn off at this time, will, when cold, present a porous 

 • tructure, — a sure indication that the furnace is not working well, and that 

 the slag itself contains much of the ore in the form of a silicate. 



4 . Composition of the gas in various parts of tlie furnace during its opera- 

 tion. — The analyses lately made by Ebelnian are the most accurate and best 

 detailed that we are in possession of. What follows has reference to a fur- 

 nace worked with charcoal. 



Gas taken from the mouth of the furnace and dried: — 



Carbonic acirl .. .. ..12 88 



Ciirbontc oxide .. .. .. 2;i'51 



Hydrogen .. .. .. .. 582 



Nitrosren .. .. .. .. 57'"y 



The vapour of water in a hundred volumes of this gas, varies from nine to 

 fourteen volumes. Examinations made at different times show the propor- 

 tion of hydrogen and nitrogen to be nearly uniform, and that the sum of the 

 Tolunies of carbonic acid and carbonic oxide is constant, but that there is a 

 variation in their respective proportions. 



(jas taken from the interior of the fire-room at 5 to 10, and 13 to 17 feel 

 from the mouth (fire room 36 feet). From five to ten feet the proportion 

 of moisture diminishes, the other ingredients remaining about the same. 

 From 13 to 17 feet the proportion of carbonic oxide increases, while the 

 aarbonic acid and hydrogen diminish. 



Gas from the bottom of the fire-room and top of the boshes: — This is re- 

 markable for the constancy of its composition, and for the absence of car- 

 bonic acid and v^atery vapour. Composition : — 



Carbonic oxide .. .. .. 3501 



Hydrogen .. . . .. .. 1 92 



Nitrogen .. .. .. .. 63'07 



Gat from the bottom of the boshes and commencement of the hearth ; — 

 Carboidc acid .. ,. .. (i-31 



('arbonic oxide .. .. .. 41*59 



Hydrogen .. .. .. .. 1*42 



Nitrogen .. .. .. ,. SGGb 



Gas from the neighbourhood of the iuyer: — 



Carbonic oxide .. .. .. 5r3i 



Hydrogen .. ., ,, ..1-25 



Nitrogen . . . . . .. 47 40 



The two last statements would appear to contradict the rules previously 

 laid down, as regulating the operation of the blast furnace ; for, according 

 to them, the proportion of carbonic oxide, at the top of the boshes, should 

 be a little greater than in the hearth, whereas the reverse would appear to 

 be the case by the analyses here given. Besides, from a glance at the com- 

 position of the three last gases alluded to, it would appear that the gaseous 

 products, as they ascended the furnace, lost completely a portion of the car- 

 bonic oxide, without a replacement by carbonic acid or oltier compound ; in 

 other words, a portion of it would appear to be completely annihilated, which 

 of course is an impossibility. This apparent anomaly is easdy accounted 

 for, when it is stated how the gas was collected. 



In order to obtain the gas from different portions of the furnace, holes 

 were bored into the side, and a tube inserted, by which it was drawn off. 

 Allusion has already been ccade to the fact that a pasty mass adheres to the 

 ridei of the hearth, containing silicate of iron and charcoal, in which there 

 i« a constant reduction of the iron, with the formation of carbonic oxide. 

 How it is evident that the gas drawn off by a hole bored into the side of the 

 beanh, will be largely mixed with this carbonic oxide forming in the imme- 

 diate neighbourhood of the opening, and that it cannot serve as an index to 

 the character of gas passing through the centre of the hearth. M Ebeliuan 

 was aware of this fact, but he was not able to overcome the difficulties in 

 tlia way of obtaiuing the gat uader the proper circumstances. 



Gas taken at the tuyer. — Here it is little else than atmosphere mixed with 

 a few per cent, of carlmnic acid. 



From these results it will not be difficult to admit, that the oxygen of the 

 air ia converted immediately into carbonic acid, which is rapidly changed 

 into carbonic oxide, under the influence of an excess of carbon and the high 

 temperature developed near the tuyer. 



5. The causes that render necessary the great heat of the blast furnace. — 

 The weight of the ore. flux, and combustible, which enters the furnace, being 

 only one-half that of the ascending column, and as the specific heat of these 

 three materials is very much below that of the gas of the ascending mass, it 

 is not the heating of them that explains the necessity of the very great heat 

 of the blast furnace. But the principal cooling causes are, — 



1. The drying of the ore, flux, and coal, and the expulsion of carbonic 

 acid from the flux, &c., rendering much of the heat latent; for what was 

 solid is now transformed to the gaseous state. 



2. The reduction of the ore, or in other words, the transformation of the 

 solid oxygen of the ore into gaseous oxygen. If the ore has been deprived 

 of its oxygen by the action of carbonic oxide, with the formation of carbonic 

 acid, the heat rendered latent by the oxygen, is compensated for by the heat 

 developed by the reaction between the oxygen and carbonic oxide; which is 

 the character of the operation that principally takes place in the lower part 

 of the fire-room. If the ore has been deprived of its oxygen by the direct 

 action of the coal, the amount of heat rendered latent is enormous, as already 

 stated ; for carbonic oxide is the result of this reaction, and the amount of 

 heat developed by it falls far short of that rendered latent by the oxygen 

 that has entered into its formation, assuming the gaseous condition, — this is 

 the character of the reduction taking place in the boshes and hearth. 



3. The conversion of the carbonic acid near the tuyer into carbonic oxide 

 has a powerful influence in cooling the upper part of the hearth ; for of the 

 6260 units of heat formed by the first action of the air upon the coal, 4662 

 are rendered latent by the conversion of this carbonic acid into carbonic 

 oxide. 



This terminates what it was proposed to treat of; it is little else than a 

 sketch of the chemistry of the blast furnace, sufficient to show its im- 

 portance. 



In a future article, some remarks will be made upon the amount of com- 

 bustible lost in the operation of this furnace, the recent methods employed 

 to prevent this loss in the complete combustion of coal, the action of the 

 hot blast, theory of the refining furnace, charring of wood, and other points 

 of interest. 



STEPHENSON'S TUBULAR BRIDGE. 



Mr. Fairbairn's Report. 



Abstract or tliorl Summary of Hesults from Experiments relntire to the 

 proposed Bridge across the Menai Strui(s, addressed to Robert Stephenson, 

 Esq. By. W. Fairbairn. 



After a series of experimenls undertaken at your request, for ascertain- 

 ing the strongest form of a Sheet li'on Tubular Bridge across the Menai 

 Straits, i have been induced, in order lo meet the requirements for such a 

 struclure, and lo ensure safety in the cuustruction, to call in the aid and 

 assistance of my friend Mr. Hudiikinson. 



The flexible nature of the material, and the diflicullies which presenleii 

 themselves in retaining the lighter descripliou of tubes in shape gave ex- 

 ceedingly anomalous results ; and having no formula on which dependence 

 could be placed for the reduction of the experiments, 1 deemed it necessary, 

 in a subject of such importance, to secure the co-operation of the first 

 authority, in order to give confidence to the Chester and Holyhead Rail- 

 way Company, with whom you are connected, and the public geuerally. 



It will be observed, that the lirst class of experiments is upon cylindri- 

 cal tubes ; — the second upon those of the elliptical form ; — and the last 

 upon the rectangular kind. Tubes of each sort have been carefully lesled, 

 and the results recorded in the order in which they were made ; and more- 

 over, each specimen had direct reference to the intended Bridge, boih as 

 regards the length and thickness, as also the depth and widih. 



In the first class of experiments, which are those of the cylindrical form, 

 the results are as follow : 



CTLINORICAL TUBES. 



19 



