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 the roots of a kind of bugloss (Anchusa 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 alcohol 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.

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 circumstance 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

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 mercury is one of the metals thus combined the combination is called an AMALGAM.

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 circumstance 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 typemetal 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 we 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 anti

mony 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. 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 suddenly 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 then 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 suddenly 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 Thenard, the list on the left hand contains those alloys which have a greater specific gravity, and the right hand list those which have a less specific gravity, than the mean of their components.

lead and 1 part tin, burns at a red heat, and with 3 parts lead and 1 part tin it is even more combustible. An alloy of antimony and iron is so easily set on fire, that the mere action of the file is sufficient for the purpose. An alloy of chromium and lead will sometimes take fire spontaneously by mere exposure to the air, and 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 roch or rock alum, still in use. It was also manufactured 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 Vecchia, 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 form 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 times 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 large deposits of nitrate of soda in South America.

In alum works the most important minerals employed in extracting the salt, are alum stone, alum slate 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. If 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 calcined stone will not yield any alum, and if not strong enough, the stone does not readily fall to powder. By this opc ration 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,

(1) Beckmann: History of Inventions.