280 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[AuGtT3T, 



precision by a machine, the power required to produce fracture could have 

 been easily calculated, as regarded the impact. 



Mr. Farey observed, that notwithstanding the difference between the 

 results recorded in the paper, and those arrived at by Messrs. Fairbarin and 

 Hodgkinson, he was inclined to place confidence in them on account of 

 Mr. Mushet's known accuracy as an observer. He thought that the disre- 

 pute into which hot-blast iron had fallen was unmerited, that it was occa- 

 sioned by want of care, and the use of inferior materials in the manufacture. 

 He considered Mr. Neilson's invention a most important improvement in 

 nietallurgic operations, but it had been abused because, by its means, ores 

 which were formerly difficult of reduction, and therefore thrown aside, had 

 since been economically fused, without due regard to their chemical 

 constitution, and the metal produced was variable in quality and some- 

 times deficient in strength. Nevertheless, Mr. Mushet's experiments showed 

 that when proper care was exercised in the selection of the materials, and 

 in the working of the furnace, the Milton hot-blast iron, when re-melted 

 in the air-furnace, attained the high breaking weight of 610Albs., which 

 was greater than that of the best specimens of cold blast iron. Mr. Farey 

 then described at length the chemical combinations which occurred in the 

 blast furnace. The general result was, that the use of hot-blast accelerated 

 the process of separating the oxygen from the ore, and of replacing it by 

 carbon, rendering also the subsequent fusion more rapid and complete. 

 A great advantage was obtained by avoiding the cooling effect, which was 

 formerly produced by the introduction of a quantity of cold air under pres- 

 sure : the point of fusion was higher up in the furnace, and the quality of 

 the metal, when it fell into the hearth, was not injured by being blown 

 upon, as it was protected by the covering of liquid slag at a high tempera- 

 ture which descended upon it. The deoxydation and absorption of carbon 

 being facilitated, the metal contained a redundancy of carbon, notwithstand- 

 ing a less quantity of fuel was consumed. It was probable that the want of 

 strength sometimes observed might arise from the imperfect amalgamation of 

 the carbon with the metal, and this would account for the strength being 

 increased by re-melting, particularly in the air furnace, wherein the process 

 was more gradual thai in the cupola. This gradual process was not desirable 

 for cold-blast iron, in which the carbon was already well distributed; there- 

 fore in almost all foundries, the air furnaces had been replaced by cupolas, 

 as in the latter the iron was melted much more rapidly. When the use of 

 hot-blast was first proposed, it was supposed that it could not answer, be- 

 cause in all furnaces, better iron was generally made in the winter than in 

 the summer. This was a fallacy which ought not to have been entertained, 

 as it was well known that the good working arose from the dryness of the 

 air in the winter, on which account the water-regulators for the cold-blast 

 were generally abandoned, and large dry reservoirs, with or without floating 

 piston regulators, were erected in their stead. 



Mr. Field corroborated Mr. Farey's statement of the iron, when re-melted 

 in an air furnace, becoming hard and brittle. He bad in consequence aban- 

 boned their use, and made even the heaviest castings from cupolas. He at- 

 tributed the deterioration of the iron to the slowness of the process of 

 melting in the air furnace. He had found the No. 1 hot-blast pig-iron too 

 rich and weak for general purposes ; the No. 3 generally possessed the 

 greatest strength. 



Mr, Rcnnie, in answer to a question put by Mr. Farey, said, that 

 in his experiments, the transverse strength was 7T)0 lbs. ; and when 

 the bearings were 3 feet apart, the strength was H!I7 lbs., with speci- 

 mens of good quality.' He believed that in some experiments on iron made 

 with anthracite, published by Mr. Mushet in 1836, the cold-blast iron was 

 shown to be from 16 to 27 per cent, stronger than that made by the hot- 

 blast process. This might have arisen from peculiar circumstances, as Mr. 

 Crane, of Ynischedwyn, had shown him a pig of hot-blast iron, which had 

 resisted upwards of a hundred blows of a sledge-hammer, while the ordinary 

 cold-blast pigs were generally broken by about a dozen blows. From the 

 discrepancy shown by the various experiments, he was inclined to think that 

 the knowledge of the real effects of heated air, in reducing metallic ores, 

 was at present very limited. 



Mr. W. Brunton said that the only place where iron had been made with 

 anthracite and cold-blast was at the Ystahfera works, South Wales; and the 

 report by Mr. Mushet, which had been alluded to, was upon the iron made 

 there. The black band iron-stone had recently been found at the Beaufort 

 iron-works, South Wales ; and as the furnaces were now blown with heated 

 air, a large quantity of good soft iron was produced. That mine had been 

 tried in the raw state, but the result had, he believed, been doubtful. 



Mr. Davison submitted that the want of strength, which was complained 

 of in the hot-blast iron, might in some degree arise from the use of raw coal 

 instead of coke in the blast furnace, as the sulphur and other deleterious 

 matters, which were formerly got rid of in the process of coking, were now 

 introduced to the furnace, and probably combined with the iron. 



Mr. Vignoles agreed with Mr. Lowe, that the hygrometric state of the 

 atmosphere bad much influence on the quality of the iron produced. It was 

 found in India that even with the rich haematite ores and charcoal, which 

 were solely used by the native workers of metal, good iron could not be 

 made when the air was charged with moisture; but that during the hot dry- 

 winds the best metal was produced. 



» Phil. Trans. 1818, p. 133. 



Mr. Carpmael said, that during a recent visit to the Ystalyfera iron-works, 

 he had tried some experiments on the strength of the iron then being made, 

 The bars were 1 inch square, placed upon bearings 4 feet 6 inches apart, 

 and were carefully and gradually weighted, the deflection being ascertained 

 by an apparatus for the purpose. 



No. 1 specimen, loaded with 5SS lbs., deflected H inch, and sprung back 

 when unloaded without any permanent set. The weights were replaced, 

 and additions made up to 690 lbs., at which point it broke. 



No. 2 specimen, with 660 lbs., deflected li inch; with 718 lbs. it deflected 

 1| inch, and broke with 742 lbs. 



No. 3 specimen, with 578 lbs. deflected l-g, inch; with 634 lbs. it 

 deflected l-j% inch, and broke with 774 lbs. 



At the Ynischedwyn works, where hot blast and anthracite were used for 

 smelting the ore, the pig iron exhibited greater strength than any Scotch 

 iron that he had ever seen. It appeared to him that, in the Scotch iron- 

 works, the object was to produce a large quantity of metal without due regard 

 to its quality. 



Mr. Parkes remarked, with reference to the experiments upon wrought 

 iron, that the test by blows of a hammer was not sufficiently substantive to 

 be received as authority for the actual strength of iron : it frequently oc- 

 curred in practice that bar iron, which, when tried by breaking on an anvil, 

 exhibited brittleness after being forged by a smith, had proved tough and 

 good. Neither did he conceive that the capability of a beam to sustain a 

 given weight suspended from its centre was a proof of its fituess for resisting 

 impact, torsion, and other strains to which machinery was subjected. On 

 these grounds he did not receive the experiments either of Mr. Fairbarn or 

 Mr. Mushet as satisfactory, or as true indications of the absolute strength of 

 the iron. A mode of testing should be iutroduced, which would show 

 whether the improvements in making iron affected the quality of the metal 

 produced, or whether they were restricted to charges in the method of man- 

 ufacturing. 



Mr. Farey remarked that, in Mr. Fairbaim's experiments, the deflection 

 had been carefully noted, and the power of resisting impact had been cal- 

 culated by multiplying the breaking weight in pounds into the ultimate 

 deflection in inches. 



Mr. May regretted that, upon the subject of such importance as the manu- 

 facture of cast iron and its capabiUties, so little positive information was 

 recorded. The field for scientific inquiry was very extensive, and although 

 many men of high attainments had entered upon it, at present the results 

 were not satisfactory : this, he believed was only to he accounted for by the 

 fact, that the habits of mathematical investigation of the experimenters, had 

 led them to examine the theoretical rather than the practical part of the 

 subject. His experience of Scotch hot-blast iron, induced him to declare it 

 deficient in strength and tenacity, but it did not follow that all hot-blast 

 iron should be had; on the contrary, he believed the process to be a great 

 step in metallurgical science, from which important results would be ob- 

 tained; but it had unfortunately afforded an opportunity for working up 

 inferior materials, to the manifest detriment of the founder and the engi- 

 neer. If, however, at present such was the result, it was to be hoped that 

 tin* attention of manufacturers being directed to the point, an amelioration 

 would be speedily introduced, and to this the discussion by the members of 

 tbc institution might materially contribute, and thus a great benefit woidd 

 be conferred on the mechanical world. 



Mr. Mackain objected to the condemnation of Scotch hot-blast iron, as he 

 had found much of it fit for general purposes, although it was not so strong 

 as that made with cold-blast. 



Mr. Ransome corroborated Mr. May's opinion of Scotch iron. It was so 

 weak that the pigs frequently broke in unloading ; it was necessary to mix a 

 large quantity of old iron with it, in order to give the castings for machinery 

 the requisite amount of strength. 



Mr. Nasmyth had used great quantities of Scotch iron, both for large and 

 small castings, and could not rely upon it for machinery : it was deficient in 

 strength, and the contraction of the metal in cooling was so great as to 

 cause frequent losses to the founders who employed it. Indeed he conceived 

 that nothing but the lowness of its price had caused it to be so extensivelj 

 used; yet, in his opinion, this reduced commercial value marked its infe- 

 riority for there must exist some good reason why hot-blast iron should only 

 sell for 45s. to 50s. per ton, when cold-blast iron cost 80s. or 90s. He had 

 for a long time used but little of it, and that only to mix with the harder 

 qualities of iron. He did not attach much faith to experiments tried upon 

 bars of such small dimensions, and merely by suspending weights to them. 

 lie was of opinion that the masses of iron should be of larger dimensions, 

 and that they should be tried under similar circumstances to those under 

 which they were intended to be used. 



Mr. Davison said, that some years since, the framing for supporting one of 

 the large vats at Messrs. Truman and Co.'s brewery, weighing 100 tons 

 when full, had been cast o^cold-blast Welsh iron, and had stood well 

 to the present time ; but that of a precisely similar set of castings made from 

 Scotch iron, two girders had broken the first time the vat was filled. 



Mr. Field stated that the high character which had been obtained by the 

 guns from the Carron Foundry was to be, in a great measure, attributed to 

 the care with which the iron employed was selected and mixed. A simple 

 method was in use there for ascertaining the comparative strength of dif- 



