1841.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL 



263 



maker of this country, yet the whole of his nietaUic produce, in pass- 

 ing through the furnace, must have, in the first instance, been sulijected 

 to this process of steelification, before it absorbed enough of carbon to 

 constitute it white cast iron. It may, however, be produced at any 

 time artificially, by exposing white cast iron, particularly of that 

 quality that merges on the steel-grained, in an open or covered fur- 

 nace for some time to the action of a red heat, the time of exposure 

 to be commensurate to the thickness of the iron employed. This 

 operation has the etiect of discharging the white or lamellar fracture, 

 and substituting in its place one of a grayish colour, very dense, and 

 minutely steel-grained, the process itself being one of decarbonization, 

 and which, from its colour and softness under tlie file, ought not to be 

 taken, as it sometimes is, for a manifestation of an increased quantity 

 of carbon in the iron. 



2ndly, as white cast iron occupies a position between steel-grained 

 and graphite or gray iron, and is frequently found merging in both, 

 it of course possesses a variety of quality and character greater than 

 either of the other tw^o, so as to render the details of experiments 

 made with this variety of the metal subject to greater uncertaintv 

 than with the graphite or steel-grained. 



Dr. Ure has assigned no definite quantity of carbon to the steel- 

 grained iron, but that, in his estimation, it possesses a notable propor- 

 tion, may be gathered from what foUovi's: he assigns to white cast 

 iron a maximum dose of .V^ per cent., and further states that with a 

 proportion of 4A per cent, it still retains its white or lamellar fracture. 

 So that in the absence of more correct data, it may be inferred that 

 when the change to steel-grained iron has taken place, the iron has 

 lost 1 per cent, and still retains about 3i per cent, of carbon, so that 

 as it regards carbon, the iron is in the same situation with good 

 foundry iron, but observe the difiference when this theory is tested by 

 practice — the foundry iron will melt in an air furnace, and come out 

 as fluid as water, while the steel-grained iron, under the same circum- 

 stances would not melt at all, but pass rapidly into the state of mal- 

 leable iron. 



3rdly, graphite or gray cast iron first makes its appearance by small 

 dark specks inserted on the fracture of the white iron, and at this 

 stage it is said to be mottled when those specks cover the entire sui'- 

 face, and receive, from the addition of more carbon, some degree of 

 lustre, the iron is said to be bright gray ; as the fracture becomes more 

 open, and the colour darker, it is called dark gray iron; and when 

 uniformly open throughout with a smooth surface, it is called best 

 foundry iron. 



Hitherto it had been supposed and believed that white cast iron 

 contained a much less quantity of carbon — that the change of fracture 

 from white to gray was in consequence of the iron absorbing or be- 

 coming united with a large share of that substance — that whatever 

 carbon white iron contained, the graphite was so much in addition, 

 and never considered as a symptom of its abatement. 



Dr. Ure, however, holds a contrary opinion ; according to him, the 

 greatest quantity of carbon which can be united to the metal is in the 

 state of white iron, and may be to the extent of 5i per cent, as the 

 iron becomes more gray by the addition of carbonaceous matter in 

 the furnace, the quantity of carbon in it diminishes inversely to 3i or 

 4 per cent. This I confess is a paradox of difficult solution, as it in- 

 volves, to a certain extent, the operation of substracting during a pro- 

 cess of repeated additions. 



Independent of this, the new theory is to me abundantly perplexing, 

 as the student has to deal with carbon in a considerable variety of 

 states with which he bad not been formerly familiar. We have " free 

 carbon, residuum of plumbago and carbon, graphite or plumbago, 

 combined carbon, carbon uruiltered, carbon in mechanical mixture, 

 carbon in a state of alteration, &c." The most of this is new and 

 strange to me, but I may inquire whether Dr. Ure ever separated 

 carbon from cast iron by mechanical means that were not magnetic. 



Were the new theory true, we should be obliged to abandon the old 

 legitimate conclusion that iron and steel were fusible in proportion to 

 the carbon they contained, but now inversely, seeing white pig iron, 

 which is said to contain the most carbon, is much more infusible than 

 gray iron. 



The process of refining pig iron for the manufacture of bar iron, 

 would, under Dr. Ure's system, be no longer a decarbonating operation, 

 but the reverse ; for when the gray pig iron introduced into the fur- 

 nace, had acquired the white or lamellar fracture, it would be found 

 to have absorbed or taken up 1-^ of carbon in addition, being the 

 difference between 3^, the utmost that forge iron may be supposed to 

 contain, and 5^, the quantity assigned to white iron, and this during 

 an operation of the most severe decarbonization with which we are 

 acquainted. 



In like manner, suppose a founder was to charge his air-fumace 

 with 2000 ft. or any other quantity of gray pig iron, which is known 



to contain 3i per cent, of carbon by repeated fusions, accompanied 

 with a considerable loss of iron, it would at last become possessed of 

 the white or lamellar fracture, and have acquired nearly 2 per cent, 

 more of carbon while passing through a reiietition of consecutive 

 fusions. To believe this for one moment appears to me the climax of 

 absurdity. 



Again, in the blast furnace a comparatively limited quantity of coke 

 only is necessary merely to fuse the charge, and cause the whole to 

 flow in one common slag, without any portion of the iron being sepa- 

 rated. More coke, that is carbon, is added, separation takes place, 

 the iron becomes white, and partakes of the lamnielated fracture, and 

 may at that period"be supposed to contain the maximum dose of 5J 

 per cent, of carbon. The manufacturer, aiming at a more profitable 

 result, adds more and more carbon in the furnace, until he has attained 

 his object as to quality ; but, according to the new doctrine, while he 

 has been adding carbon in the furnace, it has been uniformly diminish- 

 ing in the pig iron. 



The pig iron maker might naturally put the following questions: 

 if white pig iron absorbs 5i per cent, of tlie fuel by weight, how is it 

 that this augmentation is not felt in the yield of our ores, but quite 

 the contrary, whereas, when the furnace is making gray iron, the yield 

 from our ores is considerably better i 



The operator in the laboratory may be apt to doubt and inquire how 

 it is that, after obtaining his metallic result in white cast iron, and 

 with a fine gloss, he can at anv time, by the addition of charcoal, 

 augment the produce of his ore from 1 to 3 per cent. This fact has 

 been known and acted upon by myself for at least 40 years, so that 

 when carburetted results have been obtained beyond the range of the 

 blast furnace, an allowance has been made in the yield of the ore for 

 their extra dose of carbon. 



The steel iron maker of Kindostan might well call in question the 

 truth of the new theory upon the most solid and philosophic grounds; 

 for were it so that white cast iron contained more carbon than gray 

 iron, he would decidedly make white iron in preference, for he could 

 do it for for one third of its present cost for charcoal ; but he has 

 continued for ages to make gray iron, for the best of all reasons, viz., 

 that his customers can, with gray iron, convert into steel a greater 

 quantity of malleable iron than they can with white.* 



On the same grounds I make no doubt that Agricola understood the 

 secret of making iron like the East Indian (gray cast iron), for the pur- 

 pose of converting, by steeping therein his malleable iron, into steel, 

 and on the same principle, namely, that of its possessing more carbon 

 to communicate to the iron. 



I shall, for the present, furnish no further objection to the theory of 

 Drs. Ure and Karsten, but conclude by stating the follovping facts as 

 being finally conclusive against it : — quantities of gray cast iron, white 

 cast iron, and steel-grained cast iron, were reduced to powder so 

 small as to pass a sieve containing 900 holes in the square inch of its 

 surface, my purpose being to form a species of metallic charcoal to be 

 used in the reduction of an ore of iron, confident that that iron which 

 contained the greatest proportion of carbon would revive from the ore 

 the greatest per centage of iron. A micaceous ore was used in pre- 

 ference, from its presenting more surface to the iron, and which con- 

 tained 70 per cent, of iron ; with the powder made from gray iron 

 40 per cent, was on the average obtained from the ore, besides making 

 good the weight of the original quantity of iron introduced into the 

 crucible, whereas, when the same experiment was carried into effect 

 with the white and steel-grained iron, not only was there no yield 

 obtained from the ore, but the original iron had sustained a loss 

 van'ing from 4 to S per cent. 



I will now make a few final remarks upon the subject of the 

 alleged quantity of carbon contained in steel, on which subject I find 

 my opinions as widely dilterent from those of Drs. Karsten and Ure as 

 upon the proportion which they allege is contained in white cast iron, 

 and which has been alluded to at large in my former communications 

 on this subject. 



Dr. Karsten, whom Dr. Ure quotes upon most occasions on the sub- 

 ject of iron and steel, says that he has found the proportions of carbon 

 in steel v-ary from Ij to "2| per cent. ; now in noticing this latter pro- 

 portion, I have no hesitation in saying that 2'i per cent, of carbon 

 united with iron would not form steel at all, but white cast iron. 

 Again, it is said that the proportion in blistered steel reaches, some- 

 times, but never exceeds, IJ per cent., so that we are led to infer that 

 some sort of steels contains 1 per cent, more carbon than that which is 

 said to be contained in steel of cementation. According to my know- 

 ledge and view of the matter, steel of any sort united with IJ per 

 cent, of carbon, would not at any degree of heat extend under the 

 hammer, or be applied to any useful purpose. 1| per cent, would be 



* See my Papers on Iron and Steel, page 670. 



