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which it has been dissolved; and the number dissolved in nitric acid, multiplied by 1.08, also represent the equivalent of dry nitric acid, or the quantity present in the solution submitted to experiment.

ALKANET. A fine red dye, obtained from Ihe roots of a kind of bugloss (Anchuta tinctoria), largely cultivated about the neighbourhood of Montpellier, and in some other parts of France. The dye is procured solely from the bark of the roots, therefore young plants, in which there is more bark in proportion to the bulk of the root than in old ones, are the most valuable. The colour is yielded readily to aleohol and to all unctuous substances, but to water it yields only a dull brown colour. The principal use of alkanet is to colour ointments, lip-salve, pomade, &c. The spirituous tincture is also employed in staining white marble.

ALLOY. Chemistry has made us acquainted with about forty-three metals, ofwhichnot more than twelve are of great and extensive use in the industrial arts. These are iron, copper, lead, tin, silver, gold, mercury, zine, platinum, arsenie, antimony, and bismuth. In this limited list platinum is always employed in a pure state; iron, copper, lead, tin, silver, gold, and zine, are also employed in certain cases in their pure state; but in all those applications where hardness is a desirable quality two or more metals are combined, so as to form an alloy.1 Arsenie, antimony, and bismuth are too brittle to be used in a pure state.

Although the number of useful metals is so limited, the number of alloys admits of being increased to almost any extent. Thousands of alloys are possible, but hitherto not more than two or three hundred have been made; and of this number not more than about sixty have been studied with care. As it is impossible to predict the properties of a new alloy, it remains for the scientific chemist or the manufacturer to add to our knowledge on this interesting subject.

An alloy-may be regarded as a new metal, since it does not always, or even generally, represent the properties of its component parts, or the mean of those properties, which it would do if it were a mechanical mixture, as it is sometimes stated to be. The power of forming alloys is highly valuable to the manufacturer, because it enables him to create, as it were, a new metal, adapted to some of those special wants which advancing civilization is constantly suggesting to mankind. When, for example, the idea of printing with movable types had been clearly conceived, the most obvious metals for the purpose were iron, copper, tin, and lead. But the first two were found too hard, and cut the paper pressed upon them; the other two were too soft, and were flattened under the action of the printing press. At length it was discovered that by making an alloy of 1 part antimony, and 3 or 4 of lead, a new metal was produced, harder than lead, and softer than iron and copper, and which fulfilled all the conditions required. It is stated by most writers on this subject that type-metal expands, instead of contracting, in passing

(1) When mereury is one of the metals thus combined the combination is called an Amalgam.

from the fluid to the solid state; and that, were it not for this property, type could not be cast in a mould, but that each letter must be cut separately, thereby increasing the expense of printing, perhaps a hundredfold, and diminishing the benefits of this glorious art in a far greater proportion.

The Editor has recently been led to doubt this statement, from the cireumstance that the French stereotype casters cast their plates with the moulds in a vertical, instead of a horizontal, position, thereby getting a hydrostatic pressure, which assists in filling up the mould, and producing the sharpness required. In the usual method of casting type, the mould for each letter consists of two pieces of steel, kept asunder by means of a spring, but fitting accurately together when the spring is pressed between the thumb and fingers. This mould is held in the left hand of the caster; with an iron spoon in the right hand he takes up a portion of the melted metal, pours it into the mould, gives it a sudden upward jerk, in order that the metal may penetrate every portion of the mould; at the same instant he closes the mould upon the fluid mass, still further compressing it, and suddenly causing it to solidify by contact with the two comparatively large masses of metal which form the two sides of the mould. He then relaxes the spring, and shakes out the solid type. In this way eight or ten letters are cast per minute.

Now, in this operation, the fluid type-metal is made to undergo two distinct acts of compression, first by the jerk of the mould, and secondly by closing the mould upon the fluid mass, so as to compress it into a somewhat smaller space than it would otherwise occupy; and, while thus compressed, the mass of metal surrounding it chills it, and causes it to solidify. It is, we think, to this cireumstance that the sharpness of type is owing, and not to its expanding in the act of cooling. There seems to be no doubt that type-metal does not contract in cooling so much as either of its constituents in passing separately from the fluid to the solid state; but that it does contract, and not expand, seems to be proved by the fact, that when small globules of molten typometal cool, they leave a small cup or indentation at the upper part. The Editor has undertaken some experiments to determine this interesting point, and will state the results in a future article.

In filling up and bringing into contact the neighbouring parts of machinery, such as round the brass nuts in the heads of some screw-presses, lead is found not to answer, on account of its great contraction in cooling; but the alloy of lead and antimony answers very well: not, as we think, because it expands in cooling, but because it does not contract so much as lead alone.

In the example of type-metal wc see that the properties of the two metals are greatly modified. Lead is a soft, malleable metal; antimony is hard, brittle, and crystalline. The alloy is flexible, harder than lead, and softer than antimony; but, by varying the proportions of the two metals, the properties of the alloy become varied also. 6 parts lead to 1 of antimony produce an alloy used for large, soft printers' types; 3 of lead and 1 of antimony produce the metal of the smaller types: the former will bend slightly, but the latter is very hard and brittle, and will not bend at all. With larger proportions of lead a flexible alloy is obtained, adapted to the sheathing of ships. In these examples the properties of the alloy are modified by the properties of the constituent metals: when the soft lead prevails, the alloy resembles lead; by increasing the proportion of antimony the alloy becomes harder and more brittle. With 4 of lead and 1 of antimony the fracture of the resulting alloy is not reluctant like lead, nor foliated like antimony, but is nearly of the grain and colour of some kinds of steel and cast-iron. So also in alloys of tin and lead, the former contributes to the alloy some of its hardness, whiteness, and fusibility in proportion to its quantity, as in the various kinds of pewter; but in this alloy, copper and sometimes zinc or antimony are introduced in small portions. with brittle ones, brittle alloys are usually formed, if the brittle metal predominates, or even if its proportion be about equal to that of the ductile metal. But when the ductile metal is much greater than the brittle oue, the alloy is nearly always ductile. All alloys formed of brittle metals are themselves brittle.

In these examples the properties of the constituents appear to be only modified. In other examples we get new sets of properties. Thus, copper and tin are both very malleable and ductile metals. An alloy of 9 parts copper and 1 part tin is a tough, rigid metal, used in brass ordnance, and called gun-metal; it admits of neither rolling nor drawing. By increasing the proportion of tin, which is much softer than copper, we actually increase the hardness of the alloy. One-sixth of tin produces the maximum degree of hardness. With one-fourth of tin the highly elastic and sonorous bell-metal is produced, in which the brittleness rather than the hardness is increased. 2 parts copper and 1 part tin produce an alloy so hard that it cannot be cut with steel tools, but crumbles under their action; when struck with a hammer, or even snddenly warmed, it flies in pieces like glass, and displays a highly crystalline structure. It has no trace of the red colour of copper, but is quite white, and takes an exquisite polish, not greatly disposed to tarnish: this is the speculum-metal, used in reflecting telescopes.

Two parts copper and one part lead produce an inferior metal named pot-metal or cock-metal, which is so soft as frequently to be broken in driving a tap into a beer-cask.

Copper and lead do not combine so readily as copper and zinc; for if the moulds be opened before the castings become cold the lead will ooze out, and appear on the surface in globules. The same thing happens to a less extent in gun-metal, where the tin "strikes to the surface," and renders it particularly hard at those parts, from an increased proportion of tin. Moulds of brass, on the contrary, may be opened while red-hot.

The properties of an alloy may also be varied by the addition of a small quantity of a third metal. For example: brass is an alloy of copper and zinc; but the best kind of brass for turning at the lathe is made by the addition of a small quantity of lead. This, however, renders it unfit for hammering, just as brass without lead is unfit for turning.

Alloys are formed in various ways. Many are prepared by fusing the two metals in a covered crucible; but if the metals differ considerably in specific gravity, the heavier one will often sink, and the lower part of the bar or ingot will differ in composition from the upper. This may, to a great extent, be prevented by stirring the alloy with a rod of pottery ware until it solidifies. An alloy of gold and copper cast into bars, the moulds being placed perpendicularly, it was found that the upper part of the bar contained more copper than the lower. Copper and silver appear to combine easily; but it is very difficult to form a bar of their alloy of perfectly uniform composition.

In casting large bells and cannons the bottom of the casting will sometimes contain too much copper, and the top too much tin. In such case the objects must be broken and remelted, and this second fusion often corrects the defects of the first. In most alloys of three metals it is best to combine them first in pairs, and then to fuse these pairs together. for example, it is not easy to unite iron and bronze by a direct method; but if tinned iron and bronze be fused together, they unite readily. When lead is to form part of the composition of brass, it is better to melt the lead and the zinc together, and theu to add this alloy to the melting copper.

When the component parts of an alloy are separately fused and mingled together, great heat is generally evolved: thus, when zinc and copper are snddenly mixed, in the proportion to form brass, the increase of the heat is so great as to vaporize part of the zinc.

The specific gravity of an alloy is seldom the mean of its component parts. In some cases there is an increase of density; in others a diminution. In the following table, prepared by Theuard, the list on the left hand contains those alloys which have a greater specific gravity, and the right hand list tfiose which have a less specific gravity, than the mean of their components.

Increased Density, Diminished Densitt.

[blocks in formation]

Lead, tin, or zine, alloyed with the less fusible metals, copper, gold, and silver, produce alloys less malleable, when cold, than the superior metal, and, when heated barely to redness, they fly to pieces under the hammer: hence, brass, gun-metal, &c., when hot, require cautious treatment. Muntz's patent metal, which is a species of brass, can, however, be rolled at a red heat; but it must be remembered that the action of rollers is far more regular than that of the hammer, and soon gives rise to the fibrous character which, when uniformly distributed, is the clement of strength in metals.

The strength or cohesion of alloys is in general greatly superior to that of their constituents. Thus the relative weights required to tear asunder a bar one inch square of each of the following alloys is given in the subjoined tables from Muschenbrock's investigations:—

Strength of Alloys.

10 Copper, 1 Tin 32,003 lbs.

8 „ 1 „ .>6,088 „

0 „ 1 , 44,071 „

4 „ 1 35.739 „

i 1 1,017 „

1 „ 1 725 „

Strength of Cast Mi tuls of which the above Alloys were composed.

Barbary Copper 22,570 lbs.

Japan Copper 20,272 ,,

English Block Tin 0,050 „

Ditto 5,322 „

Banca Tin 3,679 ,,

Malacca Tin 3,211 „

These results show that theory and practice agree in assigning the proportion of 6 to 1 as the strongest alloy. The most reflective mixture is the weakest but one, its strength being only one-third to one-sixth that of tin, or one-twentieth that of copper, which latter metal constitutes two-thirds its amount.

In the following alloys, which are the strongest of their respective groups, the tin is always four times the quantity of the other metal; and they all confirm the remarkable fact that alloys have for the most part a greater degree of cohesion than the stronger of their constituents.

Strength of A lings.

4 English Tin, 1 Lead 10,607 lbs.

4 BaucaTin, 1 Antimony 13,480 ,,

4 M 1 Bismuth 16,692 ,,

4 English Tin, 1 Zinc 10,258 „

4 „ 1 Antimony 11,323 „

Strength of their constituent Cast Metals.

**■* 885 lbs.

Antimony 1,060 „

Zinc 2,089 „

Bismuth 3008 „

Tin 3,211 to 6,650 „

All the metals, even the most refractory, which can scareely be fused in a crucible at the greatest heat of the furnace, melt down with case when surrounded by the more fusible metals. The surfaces of the superior metal are dissolved or washed down, layer

by layer, until the whole becomes liquefied. Thus nickel is nearly as difficult of fusion as iron; but it is usefully employed with copper in German silver, to which it gives whiteness aud hardness, and renders the alloy less fusible. Platinum is a very refractory metal, being infusible at the highest heat of a furnace; yet it combines so readily with zine, tin, and arsenie, that it is dangerous to heat one of those substances in a platinum spoon, for an alloy would probably be formed, and the spoon spoiled.

Alloys are without exception more fusible than the superior metal which enters into their composition. Hard solders are usually made of the same metal they are intended to join, with the small addition of a more fusible metal. It may even be said that the fusing point of an alloy is generally lower than that of the less fusible metal which enters into its composition. When the constituent metals are nearly of the same fusibility, the alloy still fuses at a temperature iower than the fusing point of the less fusible metal. An alloy, very remarkable for its easy fusibility, is formed by combining 8 parts of bismuth with 5 of lead and 3 of tin. This alloy fuses in boiling water, and even in water at the temperature of 198° or 200° Fahr. And yet, if we caleulate the fusing point by taking the mean of the fusing points of the constituents multiplied into their mass, this will give 520°, for bismuth melts at 500°, lead at 600°, and tin at 442°, and

8 x 500 + 5 x 600 + 3 X 442 16 = 520.

Sir Isaac Newton was the discoverer of this remarkable alloy, which is called fusible metal. His proportions were 5 parts bismuth, 3 parts tin, aud 2 parts lead. By combining these three metals in various proportions, alloys are formed of various degrees of fusibility above and below the temperature of boiling water. Safety-plugs for steam-boilers have been formed in this way. A hole made in the boiler is stopped with one of these plugs, and it was supposed that if from any cause, such as the derangement of the safety valve, steam above the usual temperature and pressure be formed, it would fuse the plug of fusible metal, and thus foree its way out through the aperture instead of bursting the boiler. [See BiSmutH.] If mereury be added to the constituents of fusible metal, the alloy is still more fusible, and is sometimes used for filling the hollows of decayed teeth.

When an alloy is left to itself after having been fused, it solidifies and crystallizes in a confused manner, and often separates into different layers of varying degrees of density.

In exposing an alloy which contains a volatile metal to a heat greater than that which is necessary to fuse it, it is in some cases decomposed, but generally not completely. A portion of the volatile metal is driven off, but a portion also still remains, and forms a stable compound with the less volatile racial.

Alloys are in general less acted on by the atmospheric air, than the metals of which they are composed. There are, however, certain exceptions, as for example, plumber's solder, which contains 2 parts lead and 1 part tin, burns at a red heat, and with 3 parts lead and 1 par* tin it is even more combustible. An alloy of ancimony and iron is so easily set on fire, that the mere action of the file is sufficient for the p.irpose. An alloy of chrominm and lead will sometimes take fire spontaneously by mere exposure to the air, aud always at a slight elevation of temperature.

When an alloy is formed of a metal which absorbs oxygen, and another which is not oxidizable, the first may be converted into an oxide, and the second retains its metallic state. This is one of the methods adopted for separating silver from lead. If both the metals of an alloy absorb oxygen, both may be converted into oxides; but if one of the two oxidizes more readily than the other, the latter may be separated almost in a pure state by suspending the operation at a certain point. In this way copper may be separated from tin.

In forming an alloy it is often necessary to protect one or both of the metals from the action of the atmosphere. Thus in combining tin and lead, resin or grease is usually put on the surface of the melting metals. In combining tin with iron, as in tinning cast-iron kettles, &c., sal-ammoniac is rubbed upon the surfaces of the hot metals in contact with each other, and thus the air is excluded; while, if any oxide is formed, it combines with the acid in the sal ammoniac, and the surface of the metal is kept bright. [See Soldering.]

ALUM is a double salt, of great use in the arts, especially for preparing mordants in dyeing and calicoprinting. It is also used in preparing and preserving skins; in candle making, for hardening and whitening the tallow; in paper-hanging it is mixed with the paste; and it is also of use in pharmacy.

The word alumen occurs in Pliny's Natural History, in which it is stated that different substances were so named, all characterised by a certain degree of astringency, and all employed in dyeing and in medicine. It has been supposed from Pliny's account that the alum of the ancients was sulphate of iron or sulphate of alumina, or a mixture of the two. The ancients do not seem to have been acquainted with our alum. It appears to have been first manufactured in the East, but at what place or period is not known. About four or five hundred years ago there was a manufacture of alum at Rochha, the Turkish name of the government which comprehends Edessa, whence the name rock or rock alum, still in use. It was also manufaetured near Smyrna and Constantinople. The first alum works in Europe are said to have been established in 1460, at Tolfa, about 6 miles from Civita Vccchia, in the territory of the Pope. The first alum works established in England were at Gisborough, in Yorkshire, in the reign of Elizabeth. Pennant says that they were first discovered by Sir Thomas Chaloner, "who observing the trees tinged with an unusual colour, made him suspicious of its being owing to some mineral in the neighbourhood. He found out that the strata abounded with an aluminous salt. At that time the English being

strangers to the method of managing it, there is a tradition that Sir Thomas was obliged to seduce some workmen from the Pope's alum works near Rome, then the greatest in Europe. If one may judge from the curse which his holiness thundered out against Sir Thomas and his fugitives, he certainly was not a little enraged, for he cursed by the very fonn that Ernulphus has left us, and not varied a tittle from that most comprehensive of imprecations. The first pits were near Gisborough, the seat of the Chaloners, who still flourish there notwithstanding his holiness's anathema." It is curious to notice after this, that in later tunes the proprietors of the English alum works farmed those of the apostolic chamber, and increased in various ways the benefit derived from them.1

The constituents of alum are sulphuric acid, alumina, an alkali and water. The alkali may be potash, soda or ammonia. Hence there are three distinct kinds of alum, depending on the alkali employed. In this country potash alum is the kind most in use. In France both potash and ammonia alum are manufactured. Soda alum occurs native in different parts of the world, especially in South America, where soda almost uniformly replaces potash; for instead of nitrate of potash, which occurs in many parts of the old continent, there are largo deposits of nitrate of soda in South America.

In alum works the most important minerals employed in extracting the salt, are alum stone, alum state and bituminous shale. The processes vary according to the nature of the mineral. Alum stone is of a white or greyish colour, and sometimes yellowish white. It contains all the constituents of alum. In the works at Tolfa it is obtained by blasting with gunpowder. H the stone be kept constantly moistened with water for about two months, it will fall to powder and yield alum by lixiviation. This, however, is not the method adopted. The alum stone is broken into small pieces, and piled on the top of a perforated dome, within which a wood fire is kindled. As the roasting proceeds a sulphurous odour is disengaged, owing to the decomposition of a portion of the sulphuric acid of the stone. The roasting is performed twice, the pieces of ore which were at the edge during the first roasting being put into the middle during the second roasting. The heat requires to be carefully regulated, for if too strong the caleined stone will not yield any alum, and if not strong enough, the stone does not readily fall to powder. By this operation the stone acquires a reddish colour. It is next arranged in rows between trenches of water, and sprinkled frequently so as always to be kept moist. In two or three days it falls to powder, but the watering is continued every day for a month. The powder thus produced is then thrown into a leaden boiler filled about two-thirds with water. It is frequently stirred during the boiling, and water is added as the evaporation goes on. When the solution is complete the fire is withdrawn, and the earthy matters allowed to subside. A cock is then opened,

(I) Beckmann: History of Inventions.

and the clear liquor drawn off into deep wooden square vessels, so constructed as to be easily taken to pieces. In these vessels the alum gradually crystallizes, and attaches itself to the sides and bottom of the vessel. The mother liquor is drawn off into shallow wooden troughs, where a fresh crop of crystals is deposited. The liquor is now of a red colour, and is mnddy, and the last crystals are mixed with this red substance. They are washed clean, and the mother liquor is pumped up into a trough, and used in subsequent processes. The alum thus produced is named Roman alum, and is highly esteemed on account of its superior purity, some other kinds of alum being contaminated by the presence of iron. Roman alum is always mixed with a little reddish powdery matter, which is easily separated. This was probably first derived from the mother liquor, and was popularly esteemed as a proof of the alum being genuine. Hence, Dr. Thomson supposes that the manufacturers add a red powder to the article after or during the process of manufacture.

Alum slate is a much more abundant mineral than alum stone. It occurs abundantly with transition slate, and is found at Whitby, and other parts of Great Britain. The alum district of Whitby consists of precipitous cliffs, bordering on the sea, and extending to a distance of about thirty miles along the coast of the German Ocean. It is a slaty rock, but sometimes occurs in balls; it is of a bluish-black colour, with a strong shade of grey. On exposure to the air, it effloresces, and acquires an aluminous taste. Being different in composition to alum stone, it requires a different treatment in the manufacture of alum from it. If it contain much lime or magnesia, it does not answer the purpose of the manufacturer. The essential ingredients are alumina and iron pyrites. The first process is to roast the ore. In Sweden, where the alum slate itself contains a large quantity of combustible matter, it is used as fuel in the roasting. A thin layer of brushwood is first covered with pieces of alum slate, and set on fire : as the combustion proceeds, new layers of alum-slate are added, in alternate layers of roasted and unroasted ore. At Whitby, coal is used as fuel. The effect of this operation is to decompose the pyrites, to convert the sulphur into sulphuric acid, and to oxidize the iron. The ore is then washed with water, to dissolve the sulphate of iron and the sulphate of alumina. For this purpose, it is put into reservoirs of wood or of masonry, and the water is left during twelve hours to act upon ore that has been twice lixiviated; the solution is then drawn off by a stop-cock in the bottom of the reservoir, and allowed to remain twelve hours on ore that has been once lixiviated. It is then left for twelve hours upon fresh ore. The solution is now saturated with sulphate of alumina and sulphate of iron, and has a specific gravity of 1.25 at the temperature of 55°. The liquor is next boiled in leaden vessels to the crystallizing point. In Sweden, the alum slate is used as the fuel, whereby the double purpose is served of evaporating the liquor and roasting the ore. During the boiling, oxide of iron falls, mixed

with sulphate of lime, if lime be present. When sufficiently concentrated, the liquor is let into square reservoirs, to crystallize. Large quantities of crystals of sulphate of iron are deposited, and these are collected by drawing off the liquor into another reservoir. When all the sulphate of iron that can be separated in this way is removed, a quantity of sulphate of potash, hydrochlorate of potash, or of putrid urine, is mixed with the liquor. By this addition, alum is formed in the liquor, and it gradually deposits itself in crystals on the sides of the vessel. These crystals are collected, and dissolved in as small a quantity of boiling water as can be used for the purpose, and the solution is poured into large wooden casks. In two or three weeks, the crystals of alum cover the sides and bottom of the vessel. The hoops are then taken off, and the staves of the casks removed, and an enormous mass of alum crystals, of the shape of the cask, is left standing, as in Fig. 26. The mass is then

[graphic]

Fig. 26. ALUM CRYSTALLIZING TATS.

pierced, to allow the mother liquor to run out. This is reserved for another operation, and the alum, being broken to pieces, is fit for the market.

Another substance from which alum is manufactured is bituminous shale. This is a slaty mineral, generally accompanying beds of coaL and, consequently, is very common in Great Britain. It is of a brownish-black colour, and when heated, burns with a pale flame and a sulphurous odour, and then becomes white. In the large alum works at Campsie, near Glasgow, the shale is extracted from the old abandoned coal-pits in the neighbourhood, which arc very extensive. This shale is described as a clay, mixed with some coal, and with that variety of iron pyrites which undergoes decomposition, and is converted into sulphate of iron by exposure to the air. The sulphate of iron thus formed acts slowly on the clay, and, in course of time, converts it into sulphate of alumina. During a long period, alum was formed from this material by simple lixiviation with water; and a large quantity of this washed shale accumulating

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