There can be no doubt, therefore, that constituents whose presence is injurious to the mechanical properties of steel, find their way towards the top of the ingot. In steel ingots destined for the manufacture of guns, it is usual to cut off the tops, which are unsound as well as impure. The importance of this procedure has been widely recognised.* It is clear that the action of liquation cannot be neglected in making large castings and forgings, and probably gives rise to fractures that have hitherto been regarded as mysterious.

In the case of pig iron it is possible to isolate products of liquation, as has been shown by M. Lencauchez,† who heated fragments of iron to a temperature of 94° for 100 hours. At the end of this time a number of spherical grains sweated out from the surface of the fragments. Analysis of these exudations showed that they contained from 4 to 6 per cent. of phosphorus, from 0.6 to 0.8 per cent. of silicon, from a trace to 1.5 per cent. of graphite carbon, and from o to 1.24 per cent. of combined carbon. original pig iron contained about 3.5 per cent. of total carbon, 2.6 of silicon, and 1.9 of phosphorus. The composition of these exudations, therefore, is that of pig iron impoverished in carbon and silicon, but considerably enriched in phosphorus.

The

If lead, tin, and zinc are melted together, and left at rest in a fused condition, no separation takes place if the proportion of tin exceeds a certain amount; but if the quantity of tin is less than this, the alloy separates into two layers, each layer consisting of a ternary alloy of the three metals. Dr. C. R. A. Wright and Mr. C. Thompson have examined the nature of this separation, and the composition of the alloys under different conditions. The heavier alloy, they found, consists of a saturated solution of zinc in lead containing tin, whilst the lighter consists of lead in zinc containing tin. The two alloys always correspond with two conjugate points on the solubility curves of zinc in lead-tin, and of lead in zinc-tin. The tin is not distributed equally in the two alloys, except when present in a particular proportion, which varies with the ratio of zinc to lead. With less tin than this, the lighter alloy takes up the excess of tin; with more, the heavier takes up the excess.

Action of Electric Currents on Molten Alloys.-In fur

* Maitland, Min. Proc. Inst. C.E., vol. lxxxix. (1887), p. 12. See also Eccles, Journ. Iron and Steel Inst., No. 1 (1888), p. 70, and the discussion on Greenwood's paper on the "Treatment of Steel by Hydraulic Pressure," Min. Proc. Inst. C.E., vol. xcviii., 1889.

+ Mém. Soc. Ing. Civils, 1887.

Proc. Roy. Soc., vol. xlv. (1889), p. 461.

E

ther tracing the analogies between alloys and saline solutions, it will be well to see what takes place when a current of electricity is passed through an alloy. Take first the case of a fluid alloy through which a current is passed. We have spoken of alloys as solutions; if they be ordinary chemical solutions it has been urged that an electric current of sufficient strength ought to decompose them, and it becomes a most important question to determine whether an ordinary metallic alloy can conduct electrolytically like a salt solution, or whether it conducts, as a metal would, that is, without being decomposed.

The question therefore arises, can a well-marked alloy, or a quasi-compound, be in the slightest degree electrolysed by an exceedingly intense electric current? Some experiments conducted by M. Gérardin,* in 1861, satisfied him that amalgams of sodium and mercury might be decomposed by an electric current, with partial separation of the constituent metals. The experiments were repeated by Dr. Obach† who employed the apparatus shown in the diagram (Fig. 26). The sodium amalgam is enclosed in the two

glass vessels, A A', and metallic communication between them is effected by opening the stop-cock, B, and sucking the amalgam into the bent tube. An atmosphere of dry hydrogen is provided, by the tubes, C C'C", and the current is transmitted through the amalgam by the battery terminals shown. Subsequent examination of the sodium amalgam proved that no separation had been effected. The composition of the amalgam was unaltered by the

*

Comptes Rendus, vol. xliii. (1861), p. 727.

+ Poggendorff's Ann. der Phys. u. Chemie, sup. vol. vii. (1876), p. 280.

passage of the current. He also used a W-shaped tube containing melted alloys, and proved that no decomposition could be observed after the passage of the current.

In 1887, at the request of the Electrolysis Committee of the British Association, the author took up the inquiry* and by employing an intense electric current from secondary cells, showed that no separation took place either in certain alloys of lead and gold, or in alloys of lead and silver, even with so strong a current as 300 ampères. The method employed is indicated by the diagram (Fig. 27). The alloy, C D, under examination was placed in cavities cut in a fire-brick,

shown at E, and the cables from a secondary battery were connected by means of copper holders with wrought-iron terminals, A B. The experiments are given in detail in the Report of the British Association for 1887, and it will be sufficient to say here that as the question at present stands, it would seem that fluid alloys conduct just like metals, and not like salt solutions; but, as Dr. Lodge has pointed out with reference to these experiments, "if the question as to the possibility of the electrolytic separation of true alloys of metals should be answered in the negative, there must surely remain a group of bodies on the borderland between alloys proper and electrolytes, among which some gradual change from wholly metallic to wholly electrolytic conduction is to be looked for."

FIG. 27.

Conduction of Electricity by Alloys at High Temperatures. -It has long been known that the electrical resistance of alloys increases as the temperature is raised, but the want of a simple and accurate pyrometer has hitherto prevented experiments being carried far in this direction. Le Chatelier, however, has shown in a recent paper,† by the aid of his pyrometer, to be hereafter described, that in metals which do not undergo any molecular change before fusion, the increase of electrical resistance is proportional to the temperature. A great number of metals seem, like iron, to undergo sharply defined molecular changes at definite temperatures, and some alloys show progressive changes, all of which facts are clearly indicated by abrupt or gradual change in resistances.

The alloys as yet worked on are brass, German silver, and an * Report British Assoc., 1887, p. 341.

+ Comptes Rendus, vol. cxi. (1890), p. 454.

alloy containing :-Copper, 70 per cent.; nickel, 18 per cent.; and iron, II per cent. These have been examined at temperatures between the ordinary temperature and their melting points.

Conduction of Electricity by Solid Alloys. In the case of solid alloys-solidified solutions of metals, that is the nature of the evidence is very different, for the passage of the electric current through solid alloys reveals the existence (1st) of certain well-defined compounds of the metals, and (2nd) affords abundant proof that in certain alloys the metals exist in allotropic states. And here it is necessary to go back chronologically, and refer to the classical mark of Matthiessen published in 1860.* He showed that the

electrical conductivity of all alloys may be graphically represented by one or other of three typical curves, which, as the diagrams

indicate, are respectively U-shaped (Fig.28), L-shaped (Fig. 29), or straight lines (Fig. 30). On adding gold to silver, for instance, there is a rapid decrease of conductivity, silver being 100, and the curve gradually turns round and then rises without any break to the point representing the conductivity of gold.

In the case of the silvercopper series, silver being 100 and copper 96, there is

a marked break in the U-shaped curve (Fig. 28) corresponding

* Phil. Trans. Roy. Soc., 1860, p. 161.

to the alloy, which contains 71.8 per cent. of silver, and this is probably a definite chemical alloy.

In the case of the L-shaped curve (Fig. 29), representing the conductivity of the copper alloys, SnCu, and SnCu, (which contain respectively 61.8 and 68.2 per cent. of copper) are probably definite compounds.* This view is confirmed by Laurie, who has shown quite recently by another † method-by determining the electromotive force of the copper series-that probably SnCu, is a chemically definite alloy.

The nature of the evidence is as follows:

Laurie finds that if the zinc plate of a Daniell cell be replaced by a compound plate, formed by joining copper and zinc, the cell has the same electromotive force as one in which zinc alone is used. This is true even if the zinc surface be only 1000 part of the copper surface. If the zinc plate be replaced by copper-zinc alloys, no deflection of the electrometer is observed as long as the alloy contains less than 67 per cent. of zinc. At this point however, a considerable deflection, practically equivalent to that given by zinc, is suddenly obtained. This result, in his opinion, may be taken as evidence of the existence of a compound of the two metals of the formula CuZn,. Alloys containing a greater proportion of zinc behave like zinc alone. Similarly in the case of tin-copper alloys, a sudden rise of electromotive force is observed when the proportion of tin in the alloy exceeds that which would be contained in a compound of the formula SnCu,. This result is in harmony with the evidence already obtained by observations of the density and thermal and electrical conductivity of the copper-tin alloys. If an alloy containing a larger percentage of tin than SnCu,, in a state of fine division, be placed in a copper cup and used in place of the zinc in a cuprous chloride cell, the excess of tin is gradually eaten out, leaving approximately the alloy SnCu,. This alloy undergoes no change if the circuit be kept closed.

Various investigators, including Wheatstone, Jules Regnault, Gaugain, Crova, Robb, Lindeck, and Hockin and Taylor, have examined the electromotive force of metallic amalgams in acid and saline liquids, and the latter investigators have shown that I part by weight of zinc in 23.6 million parts of mercury is electropositive to pure mercury in a solution of zinc sulphate. Dr. G. Gore employs two portions of very pure mercury as an electrolyte.

* See Roberts-Austen, Phil. Mag. [5], vol. viii. (1879), p. 551 ; and Lodge, ibid., p. 554.

+ Journ. Chem. Soc., 1888, p. 104.

Chemical News, vol. lxi. (1890), p. 40.