108 



THE CIVIL EXGINKKR AND ARCHITECTS JOURNAL. 



^Jt 



NE, 



fusibilitv of tliat kind of iron whicli, before the liigli temperature ne- 

 cessary for the exertion of the greatest force of allinity, can be raised 

 upon it as a solid, occasions it to pass into the fluid state, in which no 

 union can take place between it and the carbon. 



The table of proportions, as has been already observed, is a simple 

 recapitulation of the results of the fusion of bar iron with given quan- 

 tities of charcoal to exhibit the various states and qualities of cast 

 iron and cast steel. By these results it appears that less charcoal is 

 required to form white cast iron than to constitute gray cast iron, and, 

 after forty years' observation and experience this is still my decided 

 opinion. "Dr. Ure on the contrary thinks that common white pig iron 

 contains a maximum dose of carbon and that the grayest ])ig iron of 

 the blast furnace contains less. Hence it may be inferred (according 

 to the reasoning of Dr. Ure,^ that white cast iron when fused with 

 charcoal, does not increase in weight, because it is already so saturated 

 vpith carbon as to be unable to take up any more, and that gray cast 

 iron, when fused in the same way, dms increase in weiglit, because it 

 contains a comparatively small q"uantity of carbon, and can therefore 

 absorb an extra dose in Us fusion with' charcoal; but in what quantity 

 this absorption takes place, or to what extent, the reader is left to 

 guess. 



Dr. Ure, following Karsten, says that white ])ig iron contains from 

 4A to 5j per cent, of carbon, and gray iron from Sj to 4 per cent., but 

 the gray iron may, according to Dr. Ure, be considerably increased in 

 weight by its fusion with charcoal. If we suppose this increase of 

 weight to be from 2 to 2j per cent, (from experiment I know it may 

 be more), then we shall have, for the quantity of carbon in gray cast 

 iron, the original quantity, from 3^ to 4 per cent., and the experi- 

 mental quantity from :i to "h per cent., making from ■'ii to Qh per cent, 

 a proportion exceeding the maximum quantity assigned by Dr. Ure to 

 white cast iron. 



The following remarks will throw a little light upon the subject, 

 and enable us to explain the phenomena without having recourse 

 either to the theory of Drs. Ure and Karsten, or to the expedient of 

 impugning the accuracy of the table of projiortions. 



Were white pig iron of a definite character, manufactured under the 

 same cinder and circumstances in the blast furnace, and found to con- 

 tain at all times the same quantity of carbon, it might be possible to 

 arrive at some certain conclusion as to the results to be obtained by its 

 fusion with charcoal. But if we consider that the white cast iron, 

 particularly of this country, is generally made accompanied by a black 

 or blackish brown cinder, containing portions of unreduced iron, it will 

 be obvious that we have to deal with an impure and imperfect state 

 of the metal, varying in quality as the proportions of carbon, oxide of 

 iron, cr earthy matter be absent or predominant. Hence the great 

 difficulty of stating any thing definite on the subject, or of arriving at 

 any satisfactory result, as we may use many different sorts of white 

 pig iron, more or less pure, and containing more or less carbon to deal 

 with. 



By those who, like myself, have entered largely into this field of 

 investifi;ation, white cast iron has been estimated to contain from lA 

 to 2 pel- cent, of carbon, (and not from 4A to 5i per cent., as Dr. Ure 

 has it,J together with a fraction of the unreduced ore and its accom- 

 panying earthy parts in combination with the iron, even when its 

 fracture appears to be the most dense. The existence of these im- 

 purities is made most obvious in fusing white and gray cast iron in 

 crucibles, and observing their molten surfaces respectively. The 

 white iron, according to the degree of its impurity, presents upon its 

 surface a quantity of slaggy matter, varying from i to 2 per cent, on 

 the weight of the iron, w hil'e, under similar circumstances as to fusion, 

 the gray cast iron exhibits a pure convex surface without a trace of 

 slag. 



Again in the cementation of white cast iron by heating it in contact 

 with charcoal, with a view to convert it into gray iron, should the pro- 

 cess be interrupted after a few hours' exposure, the surface of the 

 iron will be found covered with minute hemispheres of slag of various 

 diameters (but none of them exceeding half a tenth of an inch), opaque, 

 contuining iron, and easily displaced. At a more advanced stage of 

 the cementation, the hemispheres of slag will be found to have parted 

 with their iron, to have become more brittle and transparent, and to 

 cover small globules of iron which (as evidence of the reduction of 

 the metallic oxide united to the iron before alluded to) have inserted 

 themselves on the surface of the liar. When white cast iron with a 

 polished surface is used in a similar experiment, the hemispheres of 

 slag and globules of iron do not make their appearance, but oozings 

 take i)lace which form themselves into highly magnetic matters with 

 a specular surface, adhering partly to the iron and partly found in the 

 charcoal, from whence they are easily withdrawn by means of a 

 magnet. 



It seems obvious from these facts, that a portion of weight may be 



thus lost (namely the oxygen of the oxide and the glass which has 

 been disentangled from the metal by a process of incessant reduction), 

 sufficient to account for white or lamellar pig iron, or some sorts of it 

 not increasing in weight when fused in contact with charcoal, in as 

 much as the sum by weight of the oxygen, an unreduced but separated 

 oxide and earth, may equal, or amount to more than, the carbon ab- 

 sorbed during the operation, and make it appear not onlv that no in- 

 crease takes place, but that actual loss is sustained without calling into 

 question the disposition which white cast iron may have to absorb or 

 repel carbon in its fusion with charcoal. 



Were it possible to obtain white cast iron as free from oxide and 

 earthy matter as gray iron, and were it to be found on experiment 

 that such iron gains no weight by its fusion with charcoal, while gray 

 iron does, I should be inclined in some measure to account for this 

 (as in my former letter) by the early fusibility of the metal, and from 

 its being a more rapid conductor of heat than gray iron, which causes 

 it to enter into fusion before an absorbing affinity can be instituted 

 between it and the charcoal, while the latter, being a worse conductor, 

 remains longer as a solid in a high temperature to absorb the carbon. 

 .Some sorts of white cast iron pass into gray iron in the crucible with 

 facility, but not with any material augmentation of weight, the oxygen, 

 oxide, and earthy matters lost being equivalent to the carbon gained. 

 In other white pig iron I have experienced a decided increase of 

 weight, while its fracture remained apparently unaltered, but more 

 frequently when the white iron was changed to ^av. 



Tlie same anomalies attach to the scale of manufacture. Different 

 ores tend, according to their constituent parts to produce various 

 qualities of iron as to their degree of carbonization, and some, when 

 smelted alone, uniformly produce white iron. 



These various shades of quality all vanish in the crucible through 

 the application and medium of lime, to which is to be added as much 

 argillaceous schist only as will convert the lime into a pure porcelain 

 slag. Fusion under these circumstances, and with -r^^ the weight of 

 iron of charcoal, will convert the most imperfect white cast iron into 

 the most beautiful carburet, equal in point of saturation of carbon to 

 any thing that can be produced in the reduction of iron ores in the 

 crucible, and superior to any thing that is produced from the blast 

 furnace. Under the most favourable circumstances, the increase of 

 weight in these cases seldom exceeds i per cent., while the same 

 experiment made with gray iron would acquire an additional weight 

 of from 2 to 2 J per cent., clearly indicating the loss which is sustained 

 in the fusion of white iron from the causes before mentioned. 



Your's, &c., 



D. MU3HET. 



Colt/ord, April -ll, 1S41. 



QUERIES. 



Sir — I should feel obliged if you, or any of your numerous correspomlents 

 could afford me any information on the subject of the iustruments aud ma- 

 chinery, which have been at various times invented for the purpose of assist- 

 ing and facilitating draughtsmen in the correct delineation of existing build- 

 ings, under different titles, as the Camera Lucida, Perspective Machine, &c. ; 

 many improvements have of late years been made in this department, and it 

 is of these that I wish to obtain information. And I cannot help thinking 

 that it is far from being an unimportant subject to the profession, as it tends 

 greatly to facilitate one great object of travel to the architect, s\z., the ob- 

 taining of strictly correct deUneations of the different structures which may 

 fall under his notice, with the least possible waste of time. In conclusion, 

 I hope that gentlemen may be induced to furuisli the names, &c. of any in- 

 struments of this description they may have seen, iu order that their relative 

 value may be known, as it has often happened in this profession as in others, 

 that inferior and inadecpiatc instruments have Ijeen employed merely through 

 ignorance of the existence of better. Hoping that you will pardon my 

 troubUng you. 



I am, Su', your humble servant, 



Archt. Angl. 



Sir — If any of your readers could give me information ou the following 

 subject, I should be obliged to them. 



How is the permanent way laid on the Greenwich arches ? what is the 

 cost of keeping it in repair :" what thickness is there of ballasting between 

 the rail and the extrados of the arch at the crown : aud what is the cause 

 of the feehng cf rigiditv, and of the jolting complained of on that line '■ 



How are these points arranged on tlie .Alanchester and Birmingham, and 

 other lines, where a railway is carried for a considerable distance on arches .' 



The comparative advantages of these methods, with an\ suggestions re- 

 specting them, will oblige 



Your obedient servant, 



iVff.vS, 18-11. A. B. 



