Chapter CXVII: Act 1895: , may be given to a married woman on applying to (6)

an oxidation product of uric acid, being obtained from it by the action of cold nitric acid, C5H4N4O3 + H2O + O = C4H2N3O4 + CO(NH2)2. It crystallizes from water in colourless rhombic prisms, containing four molecules of water of crystallization, and possesses a very acid reaction. It serves as the starting-point for the preparation of many related substances. Zinc and hydrochloric acid in the cold convert it into alloxantin (q.v.), hydroxylamine gives nitroso-barbituric acid, C4H2N2O3: NOH, baryta water gives alloxanic acid, C4H4N2O5, hot dilute nitric acid oxidizes it to parabanic acid (q.v.), hot potassium hydroxide solution hydrolyses it to urea and mesoxalic acid (q.v.) and zinc and hot hydrochloric acid convert it into dialuric acid, C4H4N2O4. M. Nencki has shown that alloxan combines with thiourea in alcoholic solution, in the presence of sulphur dioxide to form pseudothiouric acid, C5H6N4SO3. Methyl and dimethylalloxans are also known, the former being obtained on oxidation of methyl uric acid, and the latter on oxidation of caffeine (q.v..)

ALLOXANTIN, C8H4N4O7.3H2O, a product obtained by the combination of alloxan and dialuric acid, probably possessing the constitution

NH--CO CO--NH
| | | |
CO C(OH)--O--CH CO
| | | |
NH--CO CO--NH

one of the three molecules Of water bema possibly constitutional. It forms small hard prisms which become red on exposure to air containing ammonia, owing to the formation of murexide (ammonium purpurate), C8H4(NH4)N5O6. It may also be obtained by the action of sulphuretted hydrogen on alloxan. The tetramethyl derivative, amalic acid, C8(CH3)4N4O7, has been prepared by oxidizing caffeine (q.v.) with chlorine water, and forms colourless crystals which are only slightly soluble in hot water. The formation of murexide is used as a test for the presence of uric acid, which on evaporation with dilute nitric acid gives alloxantin, and by the addition of ammonia to the residue the purple red colour of murexide becomes apparent.

ALLOYS (through the Fr. aloyer, from Lat. alligare, to combine), a term generally applied to the intimate mixtures obtained by melting together two or more metals, and allowing the mass to solidify. It may conveniently be extended to similar mixtures of sulphur and selenium or tellurium, of bismuth and sulphur, of copper and cuprous oxide, and of iron and carbon, in fact to all cases in which substances can be made to mix in varying proportions without very marked indication of chemical action. The term ``alloy'' does not necessarily imply obedience to the laws of definite and multiple proportion or even uniformity throughout the material; but some alloys are homogeneous and some are chemical compounds. In what follows we shall confine our attention principally to metallic alloys.

If we melt copper and add to it about 30% of zinc, or 20% of tin, we obtain uniform liquids which when solidified are the well-known substances brass and bell-metal. These substances are for all practical purposes new metals. The difference in the appearance of brass and copper is familiar to everyone; brass is also much harder than copper and much more suitable for being turned in a lathe. Similarly, bell-metal is harder, more sonorous and more brittle than either of its components. It is almost impossible by mechanical means to detect the separate ingredients in such an alloy; we may cut or file or polish it without discovering any lack of homogeneousness. But it is not permissible to call brass a chemical compound, for we can largely alter its percentage composition without the substance losing the properties characteristic of brass; the properties change more or less continuously, the colour, for example, becoming redder with decrease in the percentage of zinc, and a paler yellow when there is more zinc. The possibility of continuously varying the percentage composition suggests analogy between an alloy and a solution, and A. Matthiessen (Phil. Trans., 1860) applied the term ``solidified solutions'' to alloys. Regarded as descriptive of the genesis of an alloy from a uniform liquid containing two or more metals, the term is not incorrect, and it may have acted as a signpost towards profitable methods of research. But modern work has shown that, although alloys sometimes contain solid solutions, the solid alloy as a whole is often far more like a conglomerate rock than a uniform solution. In fact the uniformity of brass and bell-metal is only superficial; if we adopt the methods described in the article METALLOGRAPHY, and if, after polishing a plane face on a bit of gun-metal, we etch away the surface layer and examine the new surface with a lens or a microscope, we find a complex pattern of at least two materials. Fig. 1 (Plate) is from a photograph of a bronze containing 23.3% by weight of tin. The acid used to etch the surface has darkened the parts richest in copper, while those richest in tin remained white. The two ingredients revealed by this process are not pure copper and pure tin, but each material contains both metals. In this case the white tin-rich portions are themselves a complex that can be resolved into two substances by a higher magnification. The majority of alloys, when examined thus, prove to be complexes of two or more materials, and the patterns showing the distribution of these materials throughout the alloy are of a most varied character. It is certain that the structure existing in the alloy is closely connected with the mechanical properties, such as hardness, toughness, rigidity, and so on, that make particular alloys valuable in the arts, and many efforts have been made to trace this connexion. These efforts have, in some cases, been very successful; for example, in the case of steel, which is an alloy of iron and carbon, a microscopical examination gives valuable information concerning the suitability' of a sample of steel for special purposes.

Mixture by fusion is the general method of producing an alloy, but it is not the only method possible. It would seem, indeed, that any process by which the particles of two metals are intimately mingled and brought into close contact, so that diffusion of one metal into the other can take place, is likely to result in the formation, of an alloy. For example, if vapours of the volatile metals cadmium, zinc and magnesium are allowed to act on platinum or palladium, alloys are produced. The methods of manufacture of steel by cementation, case-hardening and the Harvey process are important operations which appear to depend on the diffusion of the carburetting material into the solid metal. When a solution of silver nitrate is poured on to metallic mercury, the mercury replaces the silver in the solution, forming nitrate of mercury, and the silver is precipitated; it does not, however, appear as pure metallic silver, but in the form of crystalline needles of an alloy of silver and mercury. F. B. Mylius and O. Fromm have shown that alloys may be precipitated from dilute solutions by zinc cadmium, tin, lead and copper. Thus a strip of zinc plunged into a solution of silver sulphate, containing not more than 0.03 gramme of silver in the litre, becomes covered with a flocculent precipitate which is a true alloy of silver and zinc, and in the same way, when copper is precipitated from its sulphate by zinc, the alloy formed is brass. They have also formed in this way certain alloys or definite composition, such as AuCd3, Cu2Cd, and. more interesting still, Cu2Sn. A very similar fact, that brass may be formed by electrodeposition from a solution containing zinc and copper, has long been known. W. V. Spring has shown that by compressing a finely divided mixture of 15 parts of bismuth, 8 parts of lead, 4 parts of tin and 3 parts of cadmium, an alloy is produced which melts at 100 deg. C., that is. much below the melting-point of any of the four metals. But these methods or forming alloys, although they suggest questions of great interest, cannot receive further discussion bore.

Our knowledge of the nature of solid alloys has been much enlarged by a careful study of the process of solidification. Let us suppose that a molten mixture of two substances A and B, which at a sufficiently high temperature form a uniform liquid, and which do not combine to form definite compounds, is slowly cooled until it becomes wholly solid. The phenomena which succeed each other are then very similar, whether A and B are two metals, such as lead and tin or silver and copper, or are a pair of fused salts, or are water and common salt. All these mixtures when solidified may fairly be termed alloys.1 If a mixture of A and B be melted and then allowed to cool, a thermometer immersed in the mixture will indicate a gradually falling temperature. But when solidification commences. the thermometer will cease to fall, it may even rise slightly, and the temperature will remain almost constant for a short time. This halt in the cooling, due to the heat evolved in the solidification of the first crystals that form in the liquid is called the freezing-point of the mixture; the freezing-point can generally be observed with considerable accuracy. In the case of a pure substance, and of a certain small class of mixtures, there is no further fall in temperature until the substance has become completely solid, but, in the case of most mixtures, after the freezing-point has been reached the temperature soon begins to fall again, and as the amount of solid increases the temperature becomes lower and lower. There may be other halts in the cooling, both before and after complete solidification, due to evolution of heat in the mixture. These halts in temperature that occur during the cooling of a mixture should be carefully noted, as they give valuable information concerning the physical and chemical changes that are taking place. If we determine the freezing-points of a number of mixtures varying in composition from pure A to pure B, we can plot the freezing-point curve. In such a curve the percentage composition can be plotted horizontally and the temperature of the freezing-point vertically, as in fig. 5. In such a diagram, a point P defines a particular mixture, both as to percentage, composition and temperature; a vertical line through P corresponds to the mixture at all possible temperatures, the point Q being its freezing-point. In the case of two substances which neither form compounds nor dissolve each other in the solid state, the complete freezing-point curve takes the form shown in fig. 5. It consists of two branches AC and BC, which meet in a lowest point C. It will be seen that as we increase the percentage of B from nothing up to that of the mixture C, the freezing-point becomes lower and lower, but that if we further increase the percentage of B in the mixture, the freezing-point rises. This agrees with the well-known fact that the presence of an impurity in a substance depresses its melting-point. The mixture C has a lower freezing or melting point than that of any other mixture; it is called the eutectic mixture. All the mixtures whose composition lies between that of A and C deposit crystals of pure A when they begin to solidify, while mixtures between C and B in composition deposit crystals of pure B. Let us consider a little more closely the solidification of the mixture represented by the vertical line PCRS. As it cools from P to Q the mixture remains wholly liquid, but when the temperature Q is reached there is a halt in the cooling, due to the formation of crystals of A. The cooling soon recommences and these crystals continue to form, but at lower and lower temperatures because the still liquid part is becoming richer in B. This process goes on until the state of the remaining liquid is represented by the point C. Now crystals of B begin to form, simultaneously with the A crystals, and the composition of the remaining liquid does not alter as the solidification progresses. Consequently the temoerature does not change and there is another well-marked halt in the cooling, and this halt lasts until the mixture has become wholly solid. The corresponding changes in the case of the mixture TUVW are easily understood --the first halt at U, due to the crystallization of pure B, will probably occur at a different temperature, but the second halt, due to the simultaneous crystallization of A and B, will always occur at the same temperature whatever the composition of the mixture. It is evident that every mixture except the eutectic mixture C will have two halts in its cooling, and that its solidification will take place in two stages. Moreover, the three solids S, D and W will differ in minute structure and therefore, probably, in mechanical properties. All mixtures whose temperature lies above the line ACB are wholly liquid, hence this line is often called the ``liquidus''; all mixtures at temperatures below that of the horizontal line through C are wholly solid, hence this line is sometimes called the ``solidus,'' but in more complex cases the solidus is often curved. At temperatures between the solidus and the liquidus a mixture is partly solid and partly liquid. This general case has been discussed at length because a careful study of it will much facilitate the comprehension or the similar but more complicated cases that occur in the examination of alloys. A great many mixtures of metals have been examined in the above-mentioned way.

Fig. 6 gives the freezing-point diagram for alloys of lead and tin. We see in it exactly the features described above. The two sloping lines cutting at the eutectic point are the freezing-point curves of alloys that, when they begin to solidify, deposit crystals of lead and tin respectively. The horizontal line through the eutectic point gives the second halt in cooling, due to the simultaneous formation of lead crystals and tin crystals. In the case of this pair of metals, or indeed of any metallic alloy, we cannot see the crystals forming, nor can we easily filter them off and examine them apart from the liquid, although this has been done in a few cases. But if we polish the solid alloys, etch them if necessary, and examine them microscopically, we shall find that alloys on the load side of the diagram consist of comparatively large crystals of lead embedded in a minute complex, which is due to the simultaneous crystallization of the two metals during the solidification at the eutectic temperature. If we examine alloys on the tin side we shall find large crystals of tin embedded in the same complex. The eutectic alloy itself, fig. 2 (Plate), shows the minute complex of the tin-lead eutectic, photographed by J. A. Ewing and W. Rosenhain, and fig. 3 (Plate), photographed by F. Osmond, shows the structure of a silver-copper alloy containing considerably more silver than the eutectic. Here, the large dark masses are the silver or silver-rich substance that crystallized above the eutectic temperature, and the more minute black and white complex represents the eutectic. It is not safe to assume that the two ingredients we see are pure silver and pure copper; on the contrary, there is reason to think that the crystals of silver contain some copper uniformly diffused through them, and vice versa. It is, however, not possible to detect the copper in the silver by means of the microscope. This uniform distribution of a solid substance throughout the mass of another, so as to form a homogeneous material, is called ``solid solution,'' and we may say that solid silver can dissolve copper. Solid solutions are probably very common in alloys, so that when an alloy of two metals shows two constituents under the microscope it is never safe to infer, without further evidence, that these are the two pure metals. Sometimes the whole alloy is a uniform solid solution. This is the case with the copper-tin alloys containing less than 9% by weight of tin; a microscopic examination reveals only one material, a copper-like substance, the tin having disappeared, being in solution in the copper.

Much information as to the nature of an alloy can be obtained by placing several small ingots of the same alloy in a furnace which is above the melting-point of the alloy, and allowing the temperature to fall slowly and uniformly. We then extract one ingot after another at successively lower temperatures and chill each ingot by dropping it into water or by some other method of very rapid cooling. The chilling stereotypes the structure existing in the ingot at the moment it was withdrawn from the furnace, and we can afterwards study this structure by means of the microscope. We thus learn that the bronzes referred to above, although chemically uniform when solid, are not so when they begin to solidify, but that the liquid deposits crystals richer in copper than itself, and therefore that the residual liquid becomes richer in tin. Consequently, as the final solid is uniform, the crystals formed at first must change in composition at a later stage. We learn also that solid solutions which exist at high temperatures often break up into two materials as they cool; for example, the bronze of fig. 1, which in that figure shows two materials so plainly, if chilled at a somewhat higher temperature but when it was already solid, is found to consist of only one material; it is then a uniform solid solution. The difference between softness and hardness in ordinary steel is due to the permanence of a solid solution of carbon in iron if the steel has been chilled or very rapidly cooled, while if the steel is slowly cooled this solid solution breaks up into a minute complex of two substances which is called pearlite. The pearlite when highly magnified somewhat resembles the lead-tin eutectic of fig. 2 (Plate). In the case of steel (see IRON AND STEEL) the solid solution is very hard, while the pearlite complex is much softer. In the case of some bronzes, for example that with about 25% of tin, the solid solution is soft, and the complex into which it breaks up by slow cooling is much harder, so that the same process of heating and chilling which hardens steel will soften this bronze.

If we melt an alloy and chill it before it has wholly solidified, we often get evidence of the crystalline character of the solid matter which first forms. Fig. 4 (Plate) is the pattern found in a bronze containing 27.7% of tin when so treated. The dark, regularly oriented crystal skeletons were already solid at the moment of chilling; they are rich in copper. The lighter part surrounding them was liquid before the chill; it is rich in tin. This alloy, if allowed to solidify completely before chilling, turns into a uniform solid solution, and at still lower temperatures the solid solution breaks up into a pearlite complex. The analogy between the breaking up of a solid solution on cooling and the formation of a eutectic is obvious. Iron and phosphorus unite to form a solid solution which breaks up on cooling into a pearlite. Other cases could be quoted, but enough has been said to show the importance of solid solutions and their influence on the mechanical properties of alloys. These uniform solid solutions must not be mistaken for chemical compounds; they can, within limits, vary in composition like an ordinary liquid solution. But the occasional or indeed frequent existence of chemical compounds in alloys has now been placed beyond doubt.

We can sometimes obtain definite compounds in a pure state by the action of appropriate solvents which dissolve the rest of the alloy and do not attack the crystals of the compound. Thus, a number of copper-tin alloys when digested with hydrochloric acid leave the same crystalline residue, which on analysis proves to be the compound Cu3Sn. The bodies SbNa3, BiNa3, SnNa4, compounds of iron and molybdenum and many other substances, have also been isolated in this way. The freezing-point curve sometimes indicates the existence of chemical compounds. The simple type of curve, such as that of lead and tin, fig. 6, consisting of two downward sloping branches meeting in the eutectic point, and that of thallium and tin, the upper curve of fig. 7, certainly give no indication of chemical combination. But the curves are not always so simple as the above. The lower curve of fig. 7 gives the freezing-point curve of mercury and thallium; here A and E are the melting-points of pure mercury and pure thallium, and the branches AB and ED do not cut each other, but cut an intermediate rounded branch BCD. There are thus two eutectic alloys B and D, and the alloys with compositions between B and D have higher melting-points. The summit C of the branch BCD occurs at a percentage exactly corresponding to the formula Hg2Tl. It is probable that all the alloys of compositions between B and D, when they begin to solidify, deposit crystals of the compound; the lower eutectic B probably corresponds to a solid complex of mercury and the compound. The point B is at -60 deg. C., the lowest temperature at which any metallic substance is known to exist in the liquid state. The higher eutectic D may correspond to a complex of solid thallium and the compound; but the possible existence of solid solutions makes further investigation necessary here. The curves of fig. 7 were determined by N. S. Kurnakow and N. A. Puschin. Sometimes a freezing-point curve contains more than one intermediate summit, so that more than one compound is indicated. For example, in the curve for gold-aluminium, ignoring minor singularities, we find two intermediate summits, one at the percentage Au2Al, and another at the percentage AuAl2. Microscopic examination fully confirms the existence of these compounds. The substance AuAl2 is the most remarkable compound of two metals that has so far been discovered; although it contains so much aluminium its melting-point is as high as that of gold. It also possesses a splendid purple colour, more remarkable than that of any other metal or alloy. Many other inter-metallic compounds have been indicated by summits in freezing-point curves. For example, the system sodium-mercury has a remarkable summit at the composition NaHg2. This compound melts at 350 deg. C., a temperature far above the melting-point of either sodium or mercury. In the system potassium-mercury, the compound KHg2 is similarly indicated. In the curve for sodium-cadmium, the compound NaCd2 is plainly shown. These three examples are taken from the work of N. S. Kurnakow. Various compounds of the alkali metals with bismuth, antimony, tin and lead have been prepared in a pure state. Such are the compounds SbNa3, BiNa3, PbNa2, SuNa4. Of these, the first three are well indicated on the freezing-point curves. The intermediate summits occurring in the freezing-point curves of alloys are usually rounded; this feature is believed to be due to the partial decomposition of the compound which takes place when it melts. The formulae of the group of substances last mentioned are in harmony with the ordinary views of chemists as to valency, but the formulae NaHg2, NaCd2, NaTl2, AuAl2 are more surprising. They indicate The great gaps in our present knowledge of the subject of valency. We must not take it for granted, when the freezing-point curve gives no indication of the compound, that the compound does not exist in the solid alloy. For example, the compound Cu3Sn is not indicated in the freezing-point curve, and indeed a liquid alloy of this percentage does not begin to solidify by the formation of crystals of Cu3Sn; the liquid solidifies completely to a uniform solid solution, and only at a lower temperature does this change into crystals of the compound, the transformation being accomoanied by a considerable evolution of heat. Until recently the vast subject of inter-metallic compounds has been an unopened book to chemists. But the subject is now being vigorously studied, and, apart from its importance as a branch of descriptive chemistry, it is throwing light, and promises to throw more, on obscure parts of chemical theory.

The graphical representation of the properties of alloys can be extended so as to record all the changes, thermal and chemical, which the alloy undergoes after, as well as before, solidification, For an example of such a diagram, see the Bakerian Lecture, 1903, Phil. Trans., A. 346. The Phase Rule of Willard Gibbs, especially as developed by Bakhuis Roozeboom, is a most useful guide in such investigations.

So far we have been considering alloys containing two metals; the phenomena they present are by no means simple. But when three or more metals are present, as is often the case in useful alloys, the phenomena are much more complicated. With three component metals the complete diagram giving the variations in any property must be in three dimensions, although by the use of contour lines the essential facts can be represented in a plane diagram. The following method, depending on the constancy of the sum of the three perpendiculars from any point on to the sides of an equilateral triangle, can be adopted:--Let ABC (fig. 8) be an equilateral triangle, the angular points corresponding to the three pure metals A, B, C. Then the composition of any alloy can be represented by a point P, so chosen that the perpendicular Pa on to the side BC gives the percentage of A in the alloy, and the perpendiculars Pb and Pc give the percentages of B and C respectively. Points on the side AB will correspond to binary alloys containing only A and B, and so on. If now we wish to represent the variations in some property, such as fusibility, we determine the freezing-points of a number of alloys distributed fairly uniformly over the area of the triangle, and, at each point corresponding to an alloy, we erect an ordinate at right angles to the plane of the paper and proportional in length to the freezing temperature of that alloy. We can then draw a continuous surface through the summits of all these ordinates, and so obtain a freezing-point surface, or liquidus; points above this surface will correspond to wholly liquid alloys. The ternary alloys containing bismuth, tin and lead have been studied in this way by F. Charpy and by E. S. Shepherd. We have here a comparatively simple case, as the metals do not form compounds. The solid alloy consists of crystals of pure tin in juxtaposition with crystals of almost pure lead and bismuth. these two metals dissolving each other in solid solution to the extent of a few per cent only. If now we cut the freezing-point surface by planes parallel to the base ABC we get curves giving us all the alloys whose freezing-point is the same; theee isothermals can be projected on to the plane of the triangle and are seen as dotted lines in fig. 9. The freezing surface, in this case, consists of three sheets each starting from an angular point of the surface, that is, from the freezing-point of a pure metal. The sheets meet in pairs along three lines which themselves meet in a point. In fig. 9, due to F. Charpy, these lines are projected on to the plane of the triangle as Ee, E'e and E''e. The area of the triangle is thus divided into three regions. The region PbEeE' contains all the alloys that commence their solidification by the crystallization of lead; similarly, the other two regions correspond to the initial crystallization of bismuth and tin respectively; these areas are the projections of the three sheets of the freezing-point surface. The points E, E', E'' are the eutectics of binary alloys. Alloys represented by points on Ee, when they begin to solidify, deposit crystals of lead and bismuth simultaneously; Ee is a eutectic line, as also are E'e and E''e. The alloy of the point e is the ternary eutectic; it deposits the three metals simultaneously during the whole period of its solidfication and solidifies at a constant temperature. As the lines of the surface which correspond to Ee, &c., slope downwards to their common intersection it follows that the alloy e has the lowest freezing-point of any mixture of the three metals; this freezing-point is 96 deg. C., and the alloy e contains about 32% of lead, 15.5% of tin and 52.5% of bismuth.

It is evident that any other property can be represented by similar diagrams. For example, we can construct the curve of conductivity of alloys of two metals or the surface of conductivity of ternary alloys, and so on for any measurable property.

The electrical conductivity of a metal is often very much decreased by alloying with it even small quantities of another metal. This is so when gold and silver are alloyed with each other, and is true in the case of alloys of copper. When a pure metal is cooled to a very low temperature its electrical conductivity is greatly increased, but this is not the case with an alloy. Lord Rayleigh has pointed out that the difference may arise from the heterogeneity of alloys. When a current is passed through a solid alloy, a series of Peltier effects, proportional to the current, are set up between the particles of the different metals, and these create an opposing electromotive force which is indistinguishable experimentally from a resistance. If the alloy were a true chemical compound the counteracting electromotive force should not occur; experiments in this direction are much needed.

Sir William Chandler Roberts-Austen has shown that in the case of molten alloys the conduction of electricity is apparently metallic, no transfer of matter attending the passage of the current. A group of bodies may, however, be yet discovered between alloys and electrolytes in which evidence may be found of some gradual change from wholly metallic to electrolytic conduction. A. P. Laurie has determined the electromotive force of a series of copper-zinc, copper-tin and gold-tin alloys, and as the result of his experiments he points to the existence of definite compounds. Explosive alloys have been formed by H. St Claire Deville and H. J. Debray in the case of rhodium, iridium and ruthenium, which evolve heat when they are dissolved in zinc. When the solution of the rhodium-zinc alloy is treated with hydrochloric acid, a residue is left which undergoes a change with explosive violence if it be heated in vacuo to 400 deg. . The alloy is then insoluble in ``aqua regia.'' The metals have therefore passed into an insoluble form by a comparatively slight elevation of temperature.

Surfusion

Metals do not appear to have been studied from the point of view of surfusion until 1880, when A. D. van Pieinsdijk showed that gold and silver would both pass below their actual freezing-points without becoming solid. Roberts-Austen pointed out that surfusion might be easily measured in metals and in alloys by the sensitive method of recording pyrometry perfected by him. He also showed that the crossing of curves of solubility, which had already been observed by H. le Chatelier and by A. C. A. Dahms in the case of salts, could be measured in the lead-tin alloys. The investigation of the mutual relations of partially miscible liquids, due to P. Alexejew, D. P. Konovalow, snd to P. E. Duclaux, was extended to alloys by Alder Wright. The addition of a third metal will sometimes render the mixture of two other metals homogeneous. C. T. Heyccck and F. H. Neville proved that when one metal is alloyed with a small quantity of some other metal, the solidification obeys the law of F. M. Raoult. Their experiments, although not conclusive, appear to indicate that the molecule of a metal when in dilute solution often consists of one atom. There are, however, numerous exceptions to this rule. In the cases of aluminium dissolved in tin and of mercury or bismuth in lead, it is at least probable that the molecules in solution are Al2, Hg2 and Bi2 respectively, while tin in lead appears to form a molecule of the type Sn4.

Industrial applications

Since 1875 increased attention has been devoted to the applications of the rarer metals. Thus nickel, which was formerly used in the manufacture of ``German silver'' as a substitute for silver, is now widely employed in naval construction and in the manufacture of steel armour-plate and projectiles. Alloyed with copper, it is used for the envelopes of bullets. A nickel steel containing 36% of nickel has the property of retaining an almost constant volume when heated or cooled through a considerable range of temperature; it is therefore useful for the construction of pendulums and for measures of length. Another steel containing 45% of nickel has, like platinum, the same coefficient of expansion as glass. It can therefore be employed, instead of that costly metal, in the construction of incandescent lamps where a wire has to be fused into the glass to establish electric connexion between the inside and the outside of the bulb. Manganese not only forms with iron several alloys of great interest, but alloyed with copper it is used for electrical purposes, as an alloy can thus be obtained with an electrical resistance that does not alter with change of temperature; this alloy, called manganin, is used in the construction of resistance-boxes. Chromium also, in comparatively small quantities, is taking its place as a constituent of steel axles and tires, and in the manufacture of tool-steel. Steels containing as much as 12% of tungsten are now used as a material for tools intended for turning and planing iron and steel. The peculiarity of these steels is that no quenching or tempering is required. They are normally hard and remain so, even at a faint red heat; much deeper cuts can therefore be taken at a high speed without blunting the tool. Vanadium, molybdenum and titanium may be expected soon to play an important part in the constitution of steel. Titanium is alloyed in small quantities with aluminium for use in naval architecture. Aluminium, when alloyed with a few per cent of magnesium, gains greatly in rigidity while remaining very light; this alloy, under the name of magnalium, is coming into use for small articles in which lightness and rigidity have to be combined. One of the most interesting amongst recent alloys is Conrad Heusler's alloy of copper, aluminium and manganese, which possesses magnetic properties far in excess of those of the constituent metals.

The importance is now widely recognized of considering the mechanical properties of alloys in connexion with the freezing-point curves to which reference has already been made. but the subject is a very complicated one, and all that need be said here, is that when considered in relation to their melting-points the pure metals are consistently weaker than alloys. The presence in an alloy of a eutectic which solidifies at a much lower temperature than the main mass, implies a great reduction in tenacity, especially if it is to be used above the ordinary temperature as in the case of pipes conveying super-heated steam. It has also been stated that alloys of metals with similar melting-points have higher tenacity when the atomic volumes of the constituent metals differ than when they are nearly the same.

RERERENCES.---Alloys have formed a subject of reoorts to several scientific societies. Sir W. C. Roberts-Austen's six Reports (1891 to 1904) to the Alloys Research Committee of the Institution of Mechanical Engineers, London, the last report being concluded by William Gowland; the Cantor Lectures on Alloys delivered at the Society of Arts and the Contribution a l'etude des alliages (1901), published by the Societe d'encouracement pour l'industrie nationale under the direction of the Commission des alliages (1896-1900), should be consulted. The theoretical aspect is discussed in Leon Guillet's Etude theorique des alliages metalliques (1904). W. T. Brannt's The Metallic Alloys (1896); Roberis-Austen's Introduction to the Study of Metallurgy (1902); and R. G. Thurston's Materials of Engineering, should be consulted for the more practical details. in The Iron and Steel Metallurgist, formerly The Metallographist (Boston, Mass.), and Metallurgie (Halle). Important memoirs by Ewing and Rosenhain, and by C. T. Hevcock and F. H. Neville in the Philosophical Transactions, by N. S. Kunrnakow in the Zeitschrift fur anorganische Chemie, and by E. S. Shepherd in the Journal of Physical Chemistry, may also be consulted. (W. C. R.-A.; F. lj. NE.)

1 The instructive case of the solidification of a solution of common salt in water is discussed in the article FUSION.

ALLPORT, SIR JAMES JOSEPH (1811-1892), English railway manager, born on the 27th of February 1811, was a son of William Allport, of Birmingham, and was associated with railways from an early period of his life. In 1843 he became general manager of the Birmingham and Derby railway, and in the following year, succeeded to the same position on the Newcastle and Darlington line. Six years later he assumed the charge of the Manchester, Sheffield and Lincolnshire (now the Great Central) railway, and finally, in 1853, was appointed to the general managership of the Midland railway--an office which he held continuously, with the exception of a few years between 1857 and 1860, when he was managing director to Palmer's Shipbuilding Company at Jarrow, until his retirement in 1880, when he became a director. During these twenty-seven years the Midland grew to be one of the most important railway systems in England, partly by the absorption of smaller lines and partly by the construction of two main extensions--on the south to London and on the north to Carlisle --whereby it obtained an independent through-route between the metropolis and the north. In the railvay world Sir James Allport was known as a keen tactician and a vigorous fighter, and he should be remembered as the pioneer of cheap and comfortable railway travelling. He was the first to appreciate the importance of the third-class passenger as a source of revenue, and accordingly, in 1872, he inaugurated the policy--subsequently adopted more or less completely by all the railways of Great Britain of carrying third-class passengers in well-fitted carriages at the uniform rate of one penny a mile on all trains. The diminution in the receipts from second-class passengers, which was one of the results, was regarded by some authorities as a sign of the unwisdom of his action, but to him it appeared a sufficient reason for the abolition of second-class carriages, which therefore disappeared from the Midland system in 1875, the first-class fares being at the same time substantially reduced.

He was also the first to introduce the Pullman car on British railways. Allport received the honour of knighthood in 1884. He died in London on the 25th of April 1892.

ALLPORT, SAMUEL (1816-1897), English petrologist, brother of the above, was born in Birmingham on the 23rd of January 1816, and educated in that city. Although occupied in business during the greater portion of his life, his leisure was given to geological studies, and when residing for a short period in Bahia, S. America, he made observations on the geology, published by the Geological Society in 1860. His chief work was in microscopic petrology, to the studyol which he was attracted by the investigations of Dr H. C. Sorby; and he became one of the pioneers of this branch of geology, preparing his own rock-sections with remarkable skill. The basalts of S. Staffordshire, the diorites of Warwickshire, the phonolite of the Wolf Rock (to which he first directed attention), the pitchstones of Arran and the altered igneous rocks near the Land's End were investigated and described by him during the years 1869--1879 in the Quarterly Journal of the Geological Society and in the Geological Magazine. In 1880 he was appointed librarian in Mason College, a post which he relinquished on account of ill-health in 1887. In that year the Lyell medal was awarded to him by the Geological Society. A few years later he retired to Cheltenham, where he died on the 7th of July 1897.

ALL-ROUND ATHLETICS. Specialization in athletic sports, although always existent, is to a great extent a modern product. In ancient times athletes were encouraged to excel in several branches of sport, often quite opposite in character. Thus the athlete held in highest honour at the Olympic Games (see GAMES, CLASSICAL) was the winner of the pentathlon, which consisted of running, jumping, throwing the javelin and the discus, and wrestling. All-round championships have existed for many years both in Scotland and Ireland, and in America there are both national and sectional championships. The American national championship was instituted in 1888, the winner being the athlete who succeeds in obtaining the highest marks in the following eleven events; 100 yards run; putting 16 lb. shot; running high jump; half-mile walk; throwing 16 lb. hammer; 120 yards hurdle race; pole vault; throwing 56 lb. weight; one mile run; running broad jump; quarter-mile run. In each event 1000 points are allowed for equalling the ``record,'' and an increasing number of points is taken off for performances below ``record,'' down to a certain ``standard,', below which the competitor scores nothing. For example, in the 100 yards run the time of 9 4/5 seconds represents 1000 points; that of 10 seconds scores 958, or 42 points less; 10 1/5 seconds scores 916, &c.; and below 14 1/5 seconds the competitor scores nothing. Should the record be broken 42 points are added for each 1/5 second. (See also ATHLETIC SPORTS.)

ALL SAINTS, FESTIVAL OF (Festum omnium sanctorum), also formerly known as ALL HALLOWS, or HALLOWMAS, a feast of the Catholic Church celebrated on the 1st of November in honour of all the saints, known or unknown. In the Roman Catholic Church it is a festival of the first rank, with a vigil and an octave. Common commemorations, by several churches, of the deaths of martyrs began to be celebrated in the 4th century. The first trace of a general celebration is in Antioch on the Sunday after Pentecost, and this custom is also referred to in the 74th homily of St Chrysostom (407). The origin of the festival of All Saints as celebrated in the West is, however, somewhat doubtful. In 609 or 610 Pope Boniface IV. consecrated the Pantheon at Rome to the Blessed Virgin and all the martyrs, and the feast of the dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since on the 13th of May. The idea, based on the medieval liturgiologists, that this festival was the origin of that of All Saints has now been abandoned. The latter is possibly traceable to the foundation by Gregory III. (731-741) of an oratory in St Peter's for the relics ``of the holy apostles and of all saints, martyrs and confessors, of all the just made perfect who are at rest throughout the world.'' So far as the Western Church generally is concerned, though the festival was already widely celebrated in the days of Charlemagne, it was only made of obligation throughout the Frankish empire in 835 by a decree of Louis the Pious issued ``at the instance of Pope Gregory IV. and with the assent of all the bishops,'' which fixed its celebration on the 1st of November. The festival was retained at the Reformation in the calendar of the Church of England, and also in that of many of the Lutheran churches. In the latter, in spite of attempts at revival, it has fallen into complete disuse.

ALL SOULS, DAY (Commemoratio omnium fidelimm defunctorum), the day set apart in the Roman Catholic Church for the commemoration of the faithful departed. The celebration is based on the doctrine that the souls of the faithful which at death have not been cleansed from venial sins, or have not atoned for past transgressions, cannot attain the Beatific Vision, and that they may be helped to do so by prayer and by the sacrifice of the mass. The feast falls on the 2nd of November; or on the 3rd if the 2nd is a Sunday or a festival of the first class. The practice of setting apart a special day for intercession for certain of the faithful departed is of great antiquity; but the establishment of a feast of general intercession was in the lirst instance due to Odilo, abbot of Cluny (d. 1048). The legend connected with its foundation is given by Peter Damiani in his Life of St Odilo. According to this, a pilgrim returning from the Holy Land was cast by a storm on a desolate island where dwelt a hermit. From him he learned that amid the rocks was a chasm communicating with purgatory, from which rose perpetually the groans of tortured souls, the hermit asserting that he had also heard the demons complaining of the efficacy of the prayers of the faithful, and especially of the monks of Cluny, in rescuing their victims. On returning home the pilgrim hastened to inform the abbot of Cluny, who forthwith set apart the 2nd of November as a day of intercession on the part of his community for all the souls in purgatory. The decree ordaining the celebration is printed in the Bollandist Acta Sanctorum ( Saec. VI, pt. i. p. 585). From Cluny the custom spread to the other houses of the Cluniac order, was soon adopted in several dioceses in France, and spread thence throughout the Western Church. At the Reformation the celebration of All Souls' Day was abolished in the Church of England, though it has been renewed in certain churches in connexion with the ``Catholic revival.'' Among continental Protestants its tradition lias been more tenaciously maintained. Even Luther's influence was not sufficient to abolish its celebration in Saxony during his lifetime; and, though its ecclesiastical sanction lapsed before long even in the Lutheran Church, its memory survives strongly in popular custom. Just as it is the custom of French people, of all ranks and creeds, to decorate the graves of their dead on the jour des morts, so in Germany the people stream to the grave-yards once a year with offerings of flowers.

Certain popular beliefs connected with All Souls' Day are of pagan origin and immemorial antiquity. Thus the dead are believed by the peasantry of many Catholic countries to return to their former homes on All Souls' Night and partake of the food of the living. In Tirol cakes are left for them on the table and the room kept warm for their comfort. In Brittany the people flock into the cemeteries at nightfall to kneel bare-headed at the graves of their loved ones, and to toll the hollow of the tombstone with holy water or to pour libations of milk upon it, and at bedtime the supper is left on the table for the soul's refreshment.

ALLSTON, WASHINGTON (1770-1843), American historical painter and poet, was born on the 5th of November 1779 at Waccamaw, South Carolina, where his father was a planter. He graduated at Harvard in 1800, and for a short time pursued his artistic studies at Charleston with Edward Greene Maibone (1777-1807) the miniature painter, and Charles Fraser (1782-1860). With the former, in 1801, he went to London, and entered the Royal Academy as a student of Benjamin West. with whom he formed a lifelong friendship. In 1804 he went to Paris, and, after a few months' residence there, to Rome, where he spent the greater part of the next four years. During this period he became intimate with Coleridge and Thorwaldsen. From 1809 to 1811 he resided in his native country, and from 1811 to 1817 he painted in England. After visiting Paris a second time, he returned to the United States, and practised his profession at Boston (1818--1850), and afterwards at Cambridge, Massachusetts, where he died on the 9th of July 1843. He was elected an associate of the Royal Academy in 1819. In colour and the management of light and shade Allston closely imitated the Venetian school, and he has hence been styled the ``American Titian.'' Many of his pictures have Biblical subjects, and Allston himself had a profoundly religious nature. His first considerable painting, ``The Dead Man Revived,'' executed shortly after his second visit to England, and now at the Pennsylvania Academy of Fine Arts in Philadelphia, gained a prize of 200 guineas. In England he also painted his ``St Peter Liberated by the Angel,'' ``Uriel in the Sun'' (at Stafford House), ``Jacob's Dream'' (at Petworth) and ``Elijah in the Wilderness.'' To the period of his residence in America belong ``The Prophet Jeremiah'' (at Yale), ``Saul and the Witch of Endor,'' ``Miriam,'' ``Beatrice,'' ``Rosalie,'' ``Spalatro's Vision of the Bloody Hand,'' and the vast but unfinished ``Belshazzar's Feast'' (in the Boston Athenaeum), at which he was working at the time of his death. As a writer, Allston shows great facility of expression and imaginative power. His friend Coleridge (a portrait of whom by Allston is in the National Gallery) said of him that he was surpassed by no man of his age in artistic and poetic genius. His literary works are--The Sylphs of the Seasons and other Poems (1813). where he displays true sympathy with nature and deep knowledge of the human heart; Monaldi (1841), a tragical romance, the scene of which is laid in Italy; and Lectures on Art, edited by his brother-in-law, R. H. Dana the novelist (1850).

See J. B. Flagg's Life and Letters of Washington Allston (New York, 1892).

ALLUVION (Lat. alluvio, washing against), a word taken from Roman law, in which it was one of the examples of accessio, that is, acquisition of property without any act being done by the acquirer. It signifies the gradual accretion of land or formation of an island by imperceptible degrees. If the accretion or formation be by a torrent or flood, the property in the severed portion or new island continues with the original owner until the trees, if any, swept away with it take root in the ground. Alluvion never attached at all in the case of agri limitati, that is, lands belonging to the state and leased or sold in plots. Dig. xli. 1, 7, is the main authority. English law is in general agreement (except as to agri limitati) with Roman, as appears from the judgment in Foster v. Wright, 1878, 4 C.P.D. 438. The Scottish law, as laid down by the House of Lords in Earl of Zetland v. Glover Incorporation, 1872, L.R. 2 H.L., Sc., 70, is in accordance with the English. (See WATER RIGHTS.)

ALLUVIUM, soil or land deposited by running water. All streams, from the tiniest rill to the greatest river, are continually engaged in transporting downstream solid particles of rock, the product of weathering agencies in the area which they drain. Since the capacity of a stream to carry matter in suspension is proportional to its velocity, it follows that any circumstance tending to retard the rate of flow will induce deposition. Thus a fall in the gradient at any point in the course of a stream; any snag, projection or dam, impeding the current; the reduced velocity caused by the overflowing of streams in flood and the dissipation of their energy where they enter a lake or the sea, are all contributing causes to alluviation, or the deposition of streamborne sediment. It is evident from the foregoing remarks, that while even the smallest stream may make deposits of alluvial character it is in the flood-plains and deltas of large rivers that the great alluvial deposits are to be found. The finer material constituting alluvium, often described as ``silt,'' is sand and mud. Although it may be exceedingly fine-grained, there is usually very little clay in alluvium. The larger materials include gravel of all degrees of coarseness; carbonaceous matter is often an important element. The amount of solid matter borne by large streams is enormous; many rivers derive their names from the colour thereby imparted to the water, e.g. Hwang Ho = Yellow river, Missouri = Big Muddy, the Red river, &c. It has been estimated that the Mississippi annually carries 406 1/4 million tons of sediment to the sea; the Hwang Ho 796 million tons; the Po 62 million tons. Many shallow lakes have been completely filled with alluvium and their sites are now occupied by fertile plains; this process may be seen in operation almost anywhere; a good illustration is the delta of the Rhone in Lake Geneva. Alluvial deposits may be of great size. The flood-plain of the Mississippi has an area of 50,000 sq. m.; the great delta of the Ganges and Brahmaputra has an area of about 60,000 sq. m.; that of the Hwang Ho reaches out 300 m. into the sea and has a coastal border of about 400 m. Old alluvial deposits are left high above the existing level of many rivers, in the form of ``terraces'' of gravel and loam, the streams to which these owe their existence having modified their courses and cut deeper channels; such are the alluvial gravels and brick-earths upon which much of ``greater London'' is built. In some regions alluvial deposits are the resting places of gemstones and gold, platinum, &c.; it is from these deposits that the largest nuggets of gold have been obtained. Alluvial soils are almost invariably of great fertility; it is due to the alluvial mud annually deposited by the Nile that the dwellers in Egypt have been able to grow their crops for over 4000 years without artificial fertilization.