« PreviousContinue »
solids by the application of a fuid, which ter in the crude iron, which it obtained in afterward becomes consistent. And as pla- the smelting fumace, is employed, and sup. tina possesses this valuable property, it plies the place of the charcoal used in formseems reasonable to infer, that' it must also ing steel by cementation; and on the other consist of two metallic substances of differ- hand, that this substance, which prevented . ent degrees of fusibility; a supposition that the crude iron from being soft, tough, and appears to be confirmed by the discoveries infusible, is burned away, together with a of Dr. Wollaston and Mr. Tennant.
portion of the iron itself, while the remainCrude iron, and steel of a uniform tex. der is left in a much purer state. ture, consist therefore of a fusible combina- These are facts observed at the furnaces. tion of iron with the combustible substance But the observations and inquiries of the of the coal, or something which is imparted chemist must be carried further, in order to from it; the crude iron differing from the determine what it is that iron gains or loses steel simply in being overdosed with car- at the time of its conversion into its vabon, and less pure, on account of the ad- rious states. It is found, that crude iron apmixture of metallic oxide, which can scarce. proaches towards the soft state, not only by ly, perhaps, be avoided in the large process. heating with exposure to the air, which It appears therefore, that crude iron must burns the combustible addition, but likepass through the state of steel, before it can wise by fision, without the free access of become forged iron; and consequently, that air. In this case, when the fusion has been 'the fabrication of steel from this last is a complete, and the cooling gradual, it is circuitous process, which can only be re- found that a black substance is thrown up paid by the absence of those unreduced to its swface, which is more abundant the parts, which may exist in the crude iron. greyer or blacker the iron; and the same At some furges, however, where the ore, black substance is observed to coat the the lux, the fuel, and the management, are lailles of forged iron, which are used to adapted to each other, the produce affords take out the metal, and pour it into moulds steel, when duly refined. At other manu- for casting slot, and other articles. It ap. factorics, the crude iron is either refined, pears, therefore, that the heated iron, like or converted into steel, by running it into other heated fluids, is capable of holding a thin plaies, which are stratified with char- larger quantity of matter in solution than coal, and burned in a close furnace. In when cold; and that a portion of this this way the metal is retined by degrees, black substance separates during the coolwithout undergoing fusion; and if the heating, whether by the gradual effect of sur. be raised to that of cementation, the iron rounding bodies, or by the contact of the will not only be reduced, but converted into ladle, in the same manner as various salts steel. In the forges of Carinthia the grey are separated, in part, from water, by a dicrude iron is also converted either into soit minution of temperature. From chemical iron, or steel, according to the management analysis, as well as from its obvious characof a somewhat similar process. The iron ters, this black substance is found to be is fised in a large melting-pot; and a small plumbago, or the materials used to make quantity of water, being thrown upon the pencils, and commonly known by the name surface of the metal, causes a thin plate to of black lead, which is nothing but a car. congeal, which is taken off; and by con. buret of iron. tinuing the operation, the greatest part of The presence of this black matter is likethe fused iron becomes converted into wise exlubited by dissolving steel, or crude plates. To produce steel, these plates are iron, in acids, in which plumbago is inso. again fused, and kept a long time in an luble, and therefore remains behind in the elevated heat; at the same time that the form of a powder. Hence likewise is de metal is detended from the contact of the duced the cause of the black spot which air by a suthicient quantity of the vitreous remains upon steel, or crude iron, after its slag. To produce soft iron, the plates are surface has been corroded by acids; for this exposed to a continued roasting, while the spot consists of the plumbago, which remains air is constantly renewed by means of two alter the iron has disappeared by solution. pair of bellow's. The extensive surface of Solution in the sulphuric or muriatic acid the plates renders it unnecessary to use not only exhibits the plumbago contained that agitation, or stirring, which is required in iron, but likewise posse ses the advantage when fused crude iron is refined. In these of showing the state of its reduction by the processes it is evident, that the same mat. quantity of hydrogen gas which is disen. VOL. IIL
gaged: for the quantity of this gas, in like tion of the carbon follows at a greater heat. circumstances, proportional to that of Whence, in the refining of iron, the carbon the iron which is converted into oxide. is first burned, and the iron remains reThere are considerable differences between duced; and in the cementation of bar iron, the various products of the smelting fur- the metal is converted into steel, with nace in these respects ; but it is found, blisters on its surface; which most prothat the white crude iron affords the least bably arise from carbonic acid, formed by quantity of hydrogen in proportion to its the oxygen of some portions of unreduced bulk, and leaves a moderate portion of oxide uniting with the acidifiable base from plumbago ; the grey crude iron affords the charcoal. And lastly, as iron holds more hydrogen, and more plumbago than this acidifiable base, or carbon, in solation, the white; and the softest bar iron affords so likewise it may not be separable fron most hydrogeu of any, and little or no this metallic solvent, without carrying a plumbago. The quantities of hydrogen portion with it; in the same manner as gas, at a medium, by ounce measures, were salts, which erystallize in water, always take sixty-two, afforded by one hundred grains up part of the solvent in the formation of of the white crude iron : seventy-one by their crystals. the grey crude iron; and seventy-seven by It would require many volumes to eduthe malleable iron,
merate the leading uses of iron. This most Hence it may be inferred, that, in the valuable of metals is applied to so many, white crude iron, the processes of reduction and such important uses, that we cancot and cementation are both carried to a less look round us without seeing its effects, extent than in the grey crude iron, which is When we contemplate the innumerable produced by means of a stronger heat, effects of human industry, and ask ourselves excited with a larger quantity of fuel: and the simple question, Could this have been that the reduction of grey crude iron is done without iron? There is not a single still less perfect than that of the soft bar instance, which will not immediately shor iron; though this last, by the refining in its value. an open vessel, is so far from being more Iron is one of the principal ingredients cemented, that it scarcely contains any for dying black.
The stuff is first preplumbago at all.
pared with a bath of galls and logwood, It must be admitted, however, that the then with a similar bath to which verdegris solution in acids serves only to support is added, and lastly dyed in a similar bath these general conclusions, in conjunction with the addition of sulphate of iron. If it with the facts observed in the dry pro. be wished, that the colour should be parti. cesses; but cannot accurately show the cularly fine, the stuff should previously be quantities either of hydrogen or plumbago dyed of a deep blue : otherwise a browa afforded by the several kinds of iron. For may be first given with the green husks of the plumbago, as it becomes disengaged, walnuts. Silk however must not be previ. floats on the top of the sulphuric acid; ously blued with indigo, and sumach may where it gradually disappears, though in- be substituted instead of galls. Leather, soluble in that It must therefore be prepared by tanning with oak bark, is taken up by the hydrogen gas, and it is blackened by a solution of sulphate of iron. found that the volume of this air is dimi- Cotton has a very strong affinity for oxide nished by the absorption. Hence there is of iron, so that, if it be immersed in a soln. a double source of inaccuracy from the tion of any salt of iron, it assumes a cha. loss of plumbago, and the contraction of mois colour, more or less deep, according the hydrogen gas.
to the strength of the solution. The action On the whole then, since iron contains of the air on the oxide of iron deepens the carburet in a state of combination, of which colour ; and if the shade were at first deep, it may be deprived by heat with access the texture of the stuff is liable to be cor. of oxygen, which converts its carbon into roded by it. To prevent this, the cotton the carbonic acid; and since it recovers should be immersed in the solution cold, the plumbago by cementation with char- carefully. wrung, and immediately plunged coal; there can be no question, but that into a ley of potash mixed with a solution of this substance is originally afforded by the alum. After having lain in this four or fuel. It appears also, that the reduction of five hours, it is to be wrung, washed, and the metallic oxide takes place first at a dried. lower temperature; and that the combina- Mr. Brewer, to give a nankeen colour,
prepares his cotton yarn by boiling it five ret may be applied, and, after this has been
The moulds are commonly made in sand, pound to twenty of yarn, another bour. He held in wooden frames, (fig. 3 and 4, Plate then passes it through iron liquor, to every Iron-foundry.) Two of these frames, A B, gallon of which balf a pound of red chalk, (fig. 4.) are called a pair of flasks, and fit or ruddle, in powder, is added; the liquor together by pins, a a, in one flask, entering being poured off clear, after it has stood eyes, bb, in the other. A wooden pattern four hours to settle; and immerses it in an
of whatever is to be cast must first be made, alkaline lixivium. When of the proper co- exactly of the same dimensions as the article lour, for which this operation may be re. required. For an example, we have chosen peated if necessary, he dries it, as after to describe the manner of casting a roller, each of the former processes; and then such as is used for the wheels of small wage puts it into a warm lixivium, in which it is gons, the rolls of windmill heads, &c. The brought to a scald. It is afterward to be pattern is shown in fig. 5, 6, and 7: fig. 5 is soaked an hour in water made almost as sour
a plan, fig. 6 a section, and iu fig. 7 it is as lemon juice with sulphuric acid, and then shewn edgeways. This pattern is exactly washed and wrung twice. Lastly, it is to similar to the wheel which is to be cast, exbe boiled slowly an hour in a solution of cept that in place of the hole through the white soap, one pound to ten of yarn.
centre of the wheel: a pin, m, is stuck on, The ancients appear to have had the art projecting from each side in the same place of preparing a blue enamel from iron. M. that the holes will be : the use of these ping Klaproth analysed a piece of antique glass will be shown hereafter. The lower fiask, of a sapphire blue colour, transparent only A, (fig. t.) is placed on a board laid on the on the edges, two hundred grains of which ground: it is then filled with sand, and ramgave the following products : silex 163 med down, first with the rammer, (fig. 9) grains ; oxide of iron 19; alumina 3 ; oxide and afterwards with fig. 10, which is broader, of copper 1; lime 0.5. The loss was 13.5.
and smooths the work. The workman then Iron is very liable to be oxided, or con- with the trowel, (fig. 8) digs out a hole in tract rust. Conté informs us, that if fat oil the sand, and presses the pattern into it, the varnish be mixed with half, or at most four- flat surface horizontal, and fills the sand in fifths of its weight of oil of turpentine, and round the pattern, until it is exactly half buthis be applied lightly and evenly with a ried, he then takes out the pattern, and if sponge to iron or steel, and left to dry where there are any holes in the under part, where it is not exposed to dust, the metal will re. the sand is not filled round close to the pat. tain its lustre, without any danger of rust- tern, he puts in a small quantity of sand, and ing. In order to prevent gun-barrels from presses the pattern down again, until a per. rusting they are frequently browned. This fect impression of it is left in the sand, as in is done by rubbing it over, when finished, fig. 1. He now returns the pattern, and sprinwith aquafortis, or spirit of salt diluted with kles some dry sand, which has been burnt in water, and Jaying it by for a week or two the furnace, over the pattern and Aask, and till a complete coat of rust is formed. A then places the upper flask, B, (fig. 4) upon little oil is then applied, and the surface, it: two small sticks are placed upon the patbeing rubbed dry, is polished by means of tern, and the sand filled in round them; the a hard brush and a little bees-wax.
sand is ramined down by the rammers (fig. The yellow spots, called iron moulds, 9 and 10), and the two sticks drawn out, which are frequently occasioned by washing leaving holes, 11, (fig. 2) through the sand ink spots with soap, may in general be remov- in the upper flask. The workman now ed by lemon juice, or the oxalic or tartarous takes off the upper flask, B, by its two acids ; or by muriatic acid diluted with five or handles, leaving the patteru in the lower six parts of water, but this must be washed off flask; the burnt sand causes the two flasks in a minute or two. Ink spots may readily to separate exactly at the joining of the be removed by the same means. If the iron Hasks: the npper flask is now completely mould have remained so long, that the iron finished, the holes, 1 l, made by drawing out is very higlily oxided, so as to be insoluble the sticks, being left to pour in the metal, in the acid, a solution of an alkaline sulphu. and the pattern leaving a perfect print of
its upper half in the flask. The next ope- among them than the squaring of the circle ration is lifting the pattern out of the lower is among geométers. See EQUATION. flask, before which the workman wets the It is to be observed, that as in some other sand around the pattern, that it may adhere cases of cubic equations, the value of the together, and not be broken by lifting the root, though rational, is found under an ir. pattern. The two pins projecting from the rational or surd-form; because the root in wheel where the hole is to be, leave their this case is compounded of two equal surds impressions in the sand, forming two holes. with contrary signs, which destroy each é f (fig. 2) one in each flask. These boles other; as if x=5+5+5–V 5; receive the ends of a core, which is exactly then' x = 10; in like manner, in the irredu. the shape and size of tie hole required in cible case, when the root is rational, there the wheel : the core is formed of a mixture are two equal imaginary quantities, with of plaster of Paris and brick-dust, and is contrary signs, joined to real quantities; so made just the length and size of the pins in that the imaginary quantities destroy each the pattern, that it may be truly in the cen- other. Thus the expression : tre of the wheel. Fig. 2. is a section of the
' 50 + V
24500 =5+ - 5; and two flasks when put together; but the core is not put in : 11 are the holes for the metal, x 50 ✓ - 24500 =5-V 25. But and g h i k the hollow cavity to receive it.
5+ v 5+5 V – 5=10=, the The iron is melted in a furnace, and
root of the proposed equation.
Dr. Wallis seems to have intended to brought from it in a ladle (fig. 11) which has three handles, and is carried by two
shew, that there is no case of cubic equamen, the forked handle, M, giving a pur
tions irreducible, or impracticable, as he
calls it, notwithstanding the common opi chase to the man holding it, to turn over the ladle to deliver its contents. If the nion to the contrary. work is very small, the metal is conveyed where the value of the root, according to
Thus in the equation go3 - 63 r = 162, to the flasks in common ladles. The more intricate cases of iron-foundry,
Cardan's rule, is, r = 81 + ✓ - 270) as the casting of cylinders for steam engines, + 81 2700, the doctor says, crooked pipes with various passages, &c.
that the cubic root of 81 + V - 2700, are cast in moulds formed of loam or clay, may be extracted by another impossible and are done nearly in the same manner as binomial, viz. by i +iv - ; and in the the moulding of plaster cast from busts, &c. same manner, that the cubic root of 81 — but our limits will not allow us to describe V — 2700 may be extracted, and is equal these curious branches of the founder's art. to į –įv -3; from whence he infers, IRONY, in rhetoric, is when a person
that iti v
3+i-IV-3= 9, is speaks contrary to his thoughts, in order to one of the roots of the equation proposed. add force to his discourse.
And this is true: but those who will conIRRATIONAL, an appellation given to sult his algebra, y. 190, 191, will find that surd numbers and quantities. See Surd. the rule he gives is nothing but a trial, both
IRREDUCIBLE case, in algebra, is used in determining that part of the root which for that case of cubic equations where the
is without a radical sign, and that part root, according to Cardan's rule, appears
which is within : and if the original equaunder an impossible or imaginary form, and
tion had been such as to have its roots irra. yet is real. Thus in the equation, x?_-90 x- tional, his trial would never have succeeded. 100=0, the root, according to Carden's rule, Besides, it is certain, that the extracting will be x = ♡ 50 +
the cube root of 81 + V - 2700 is of the 24500 +
same degree of difficulty, as the extracting N 50-V 24500, which is an impos- the root of the original equation pol — 63 r sible expression, and yet one root is equal 162; and that both require the tri-section to 10; and the other two roots of the equa- of an angle for a perfect solution. tion are also real. Algebraists, for two IRREGULAR, in grammar, such infieccenturies, have in vain endeavoured to re- tions of words as vary from the original solve this case, and bring it under a real rules: thus we say, irregular nouns, irregul. form; and the tion is not less famous lar verbs, &c.
END OF VOL. III.
Printers 103, Goswell Street.