VANSTONE : SODIUM AMALGAMS. 261’7CCXLV. -Sodium Amalgams : Specific Volumes andElect &a 1 Conductivities.By ERNEST VANSTONE.AN account has already been given of the investigation of thethermal diagram and the determination of the specific volumes ofsolid and liquid sodium amalgams (Tram. Faraday Soc., 1911, 7,42).It wzs shown that when specific volume was plotted againstconcentration of amalgam expressed in atomic percentages, smoothcurves were obtained, although the corresponding thermal diagramshowed many discontinuities.Since the publication of the first paper, the specific volumes havebeen plotted against concentrations expressed in percentages byweight. It was shown by Meey ( Z e i t s c h . p h p i l i d Cherti., 18992618 VANSTONE : SODIUM AMALGAMS :29, 119) that the specific volume of alloys is a linear function ofthe concentration expressed in percentages by weight, hence thenew volume-concentration diagram (Fig.1) consists of a numberof straight lines, having nearly the same obliquity, and confirms theexistence of inter-metallic compounds shown by the t'hermaldiagram.The concentrations (in atomic percentages of sodium) where theFIG. 1..O 5 10 15 20 25 30 35 40 5discontinuities occur ar0 given below; those obtained by the thermalmethod are given for comparison.Concentrations.Weight per cent. Atoms per cent.36.0 83-023.6 73-516.4 63.09.4 47.55.2 32.52-8 20-0Atoms per cent.(thermal).85-2 and 83.473.563.347.5 and 51.533.317.9When the comparative slope of the lines in Fig.1 is considered,and the fact that the concentrations have t o be read from thediagram in percentages by weight and then transformed intSPECIFIC VOLUMES AND ELECTRICAL CONDUCTIVITIES. 2619atomic percentages, the agreement becween columns (2) and (3) inthe above table is as satisfactory as can be expect,ed.The Constitution of Liquid Amalgams.Many reeearches have been carried out on liquid amalgams,having f o r their object tho determination of the molecular com-plexity of metals in amalgams rich in mercury.Measurements of (1) vapour pressure, (2) E.M.F., and (3) lower-ing of freezing point show that the metal is present as a singleatom, yet they cannot prove1 that that atom is not combined witha certain number of atoms of mercury.Two other researches may be mentioned.(1) The rat- of diffu-sion of metals in mercury have been found, and when atomicdiffusivities are plotted against atomic weights, two curves areobtained; metals which do not form compounds with mercuryhave higher diffusivities and lie on one curve, whereas metalswhich are known to form compounds lie on a second curve withlower diffusivities. It has been suggested that compounds MHg,are formed in which the attached mercury retards the process ofdiffusion.(2) Bornemann and Muller (Metallurgie, 1910, 7, 396) deter-mined the electrical conductivity of liquid sodium amalgams, andobtained a marked discontinuity a t a concentration of 33.3 atomsper cent. of sodium, showing the existence of the compound NaHg,in the liquid condition.The thermal diagram indicates the existence of a t least fiveother compounds of sodium and mercury, but their existence inthe liquid condition was not made manifest by the electricalconductivity experiments.We are led to inquire why this is so.Bornemann and Muller'sexperiments were carried out a t very high temperatures, and it ispossible that all the other intermetallic compounds were disso-ciated; the compound NaHg, was stable, since it has a muchhigher melting point, namely, 360°, than the other compounds;i t lies at the maximum point on the thermal diagram; other com-pounds, with the possible exception of Na,Hg, do not showmaxima.It was thought Ghat indications of the existence of the otherintermetallic sodium-mercury compounds might be obtained ifphysical properties were investigated a t temperatures not farremoved from the melting points of the alloys.The specific volumes of liquid alloys a t l l O o , 184O, and 237Ohave already been determined.The concentration-volume diagram for llOo is shown in Fig.2It, is seen t h a t the specific volume of the liquid alloys is a linearfunction of the concentration when expressed in percentages byweight.The absence of discontinuities shows t h a t the intermetallic com-pound Na,Hg does not exist a t l l O o .A consideration of Fig. 1 shows t h a t the property of volumedoes not suffer any profound change when combination takesplace between the metals sodium and mercury, so further investi-FIG.2.gations were made by means of electrical cor1ductivit.y rneasure-ments of liquid amalgams.The Electrical C o i i d i i c t i u i t i e s of Liquid A tnalgams.The method of experiment has already been described in a formerpaper. The amalgams were kept under paraffin, and drawn upinto a capillary spiral having platinum terminals sealed into theglass a t convenient pointsSPECIFIC VOLUMES AND ELECTRICAL CONDUCTIVITIES. 2621The spiral was open a t the lower end and fitted with a glasstap a t the top. It was connected t o a hydrogen apparatus, andbefore, allowing any amalgam t o enter, it was dried and filled withdry hydrogeri.The1 capillary was 1 mm. in diameter, and the distance betweenthe platinum terminals about a metre, when unwound.Itl wascalibrated by finding the resistance of me'rcury filling the spiral.3.52-51 ' 50 '565 70 80 90 100Temperatures of approximately l l O o and 1 3 5 O were obtained byjacketing with boiling toluene and xylene.The results are given in the table below; concentrations areexpressed in atomic percentages of sodium ; the resistances referto a spira in which the resistance of mercury at. 1 7 O is 1 ohm.It will be noticed that conductivity measurements have beenmade for each alloy a t two t-emperatures differing by 2 6 O . Thevalue for the temperature-coefficient has thus been obtained2622 VANSTONE : SODIUM AMALGAMS.Electm'cal Conductivities of Liquid Amalgams.Concentra- Resistance Conduct- Resistance Conduct- Ternperature-at 107".ivity. (133") ivity. coefficient. tion.10095-3693.6489.8885.6080.8077.8975-317 1-7470.0268-080.22850-42250.58350.77490.97961.15691.21241.25321.29211.2968-4.3972-3661.7141.29051.02080-86430.82480.79790.77390.7711-0.2455 { 0.24490.24770.43340-81391.01331.16271.22481-25841.30871.30961-3208-FIG. 4.4.0652.3071.22860.98680.86000.81640.79460.76410.76350-7571-0.0 12760.002260.002380.001300.000 160.000320.0001 30.000400.00054--60 70 80 60 100Atoms of sodium per 100.The conductivity-concentration curve for 1 0 7 O is shown in Fig. 3.It is a rectangular hyperbola possessing no discontinuity. Theresults for 1 .3 5 O form a similar curve, which would lie slightlybelow that in Fig. 3DUNNINGHAM: THE SYSTEM ETHYL ETHER, ETC. 2623It will be observed that the fall in conductivity is most markedfrom 100 to 85 atoms per cent. of sodium, the conductivity a t85 per cent. being less than onefourth the value for pure sodium.It may be pointed out that thO concentIration of 85 per cent. isthat of the eutectic point in the thermal diagram.The differences in conductivity for a temperature range of 2 6 Oare small, and become much smaller as the mercury content of thealloys increases.The temperature-coefficient falls with extreme rapidity as wepass from pure sodium to alloys containing 5 and 10 atoms percent. of mercury. The coefficient has an extremely small, almostconstant value for alloys containing more than 20 atoms per cent.of mercury. This is shown in Fig. 4. The curve does not give anyindication of the formation of compounds.The conclusion to be drawn from electrical conductivity measure-ments for liquid amalgams is thus the same as from specific volumedeterminations, namely, that the intermetallic compounds ofsodium and mercury are completely dissociated in the liquidcondition.It is possible also from the present and from previous work tocompare the relative values of the properties specific volume,electrical conductivity, and freezing point in determining theconstitution of alloys, and it is quite evident that the last is farsuperior in the certainty of its indications.THE TRAININU COLLEGE,CAERLEON,MONMOUTHSEIRE