MaV 2, 1S95] 



NATURE 



19 



thruugh the same slit u(x>n the photographic plate. The further 



galvanometer can have a much lower resistance, and conse- 



(juently greater delicacy, than the nearer one, so that, while the 



line photographed on the moving sensitised [ilatc front the ne.irer 



galvanometer might represent a range of temperature of, say, 



1500 degrees, Ihe line traced liy the mirror of the further gal - 



nonicler should represent only one-tenth of this. The angular 



lUclion of the nearer mirror would not exceed the limits of 



ir sensitised plate, while the mirror of the delicate galvanometer 



pMght traverse a for larger range. Both galvanometers would 



. connected "'in parallel" with the s;ime thermo-junction : .md 



\ iously any jwrtion of the extended range which it was <Iesir- 



Ic to reflect on ihe sensitised plale could easily be caught by a 



iiiiiable adjustment of the mirror on the further galvanometer. 



H. therefore, the thermo-junction is plunged into a ma.ss of metal 



;i»>ling from say an initial temperature of 1500 degrees, the 



whole of the cooling curve could be traced liy the mirror of the 



li -^s delicate galvanometer, while only the portion greatly magni- 



■i wovdd be recorded by the mirror of the more delicate gat- 



iHimetcr. The first curve derived from the less delicate 



ivanometer woidd serve as a ''calibration curve ' for thai 



rded by the other galvanometer. 



I'.y means of diagrams exhibited on the walls of the theatre. 



irge number of cooling curves for eleclro-iron were shown, 



I being taken that the iron w.-is exceedingly pure. The points 



recalescence were well shown on these curves, which may be 



idled with interest in the 7>'(t«.f(n"//fl/M of the Institution, as 



I ring on the question ni allotro|)y of iron, which has already 



n fully discussed in a former report. The cooling-curve of an 



iiuinium-cojiper alloy was also given. This was the alloy 



riuiining6 per cent, of copper, used by Mr. Yarrow in the 



iislruction of torpedo boats for the French tloveniment. Two 



'rcc/ing |x>ints were shown, one due It) the main ma.ss, and the 



iher al a lower point due to ihe copper as.sociatcd with the 



iluminiinn. The pyrometric examination of iron-aluminium 



1 Hoys was also treated al some length, but it would be difficult 



.;ive results without reproducing the curves and the diagram 



'\\n. 



One feature that may be notice<l. however, was that the freez- 

 ing |x>int of iron alloyed with, say, one i)er cent, of aluminium, 

 is but little lower than that of iron itself; that is to say, the 

 iielling^ixiini of nearly pure iron is only slightly lowered by a 

 -nutll addition of almninium. Osmond had already shown that 

 aluminium does not prf>duce any considerable lowering of the 

 freezing ]x)int of cast-iron ; and the usually accepted idea that 

 cast-iron or steel containing aluminium is very fusible, must l)e 

 due to ihe fluidity of the metal when it is melted. 



Another interesting ]")oinl was that the samples of alloys used 

 in these experiments were kejit for some months I)eforc being 

 analy.sed. and it was found that during this time those which 

 contained from 40 lo 60 per cent, of aluminium had spontaneously 

 disintegrated, and hati fallen to powder. The powder was not 

 oxidised, but consislefl of clean metallic grains, probably result- 

 ing from chemical changes which had gradually taken place in 

 the solid alloy. Whether the iron and aluminium were in a.state 

 ■of solution or were cheitiicaliy combinetl when molten, there can 

 be little doubt that they are scj cond>ined in the metallic powder, 

 as attem[)ts to re-melt this powder have proved unsuccessful, which 

 points to the formation of an infusible compound. 



Some exjK'riments made by .Mr. Thomas Wrightson to as- 

 certain whetlur the welding of iron is attended with a fall of 

 lemperalure, as is the case in the regelalion of ice, were next 

 tiescribed. The welding was done by means of electricity and 

 observations were taken by means of the pyrometer formerly 

 described. The results have been communicated to the Royal 

 Society, and tend to show (hat the welding of iron and the 

 regelatitjn of ice are analogous ]>henomena, a point of no small 

 theoretical importance. 



In his last report the author had called attention lo the fact 



t M. .\ndre I.e Chatelier had suggested that the prejudicial 



lion of an element is due to its forming a fusible compound 



with the metallic m.iss in which it is hidden ; while, im the other 



^an<l, the presence of an elemeiu which forms an infusible com- 



|X)und with the mass, promotes the formation of a fine grain and 



imparts stronglli. The author did iu)t wish it to be su]>jK)sed, 



however, thai the action of the ailded element is due solely to its 



infusibility, or to ils jjower of firming a fusible C(un|iound with a 



lv>rtion of the mass which contains it ; for cases are numerous 



which such an explanation does not apply. In this connection 



ggestion made long ;tgo by Kaoult Pictet {Compter rcndtts^ 



' Ixxxviii. 1879. pp. S55 and i;i5). well deserved considera- 



NO. I 33 I, VOL. 52] 



tion. He itrged that there must be a connection between the 

 melting-points of metals and the periodic law of Mendeleeff ; for 

 he showed that for all metals there is a simple relation between 

 their atomic weight, the amplitude of the movement of their 

 molecules under the influence of heat, and their melting-point. 

 Pure metals w ith high melting-points^ — such as platinum, iron. 

 copper, and gold — are comparatively strong ; and, conversely, 

 metals w ith low melting-[X)ints — zinc, lea<i, cadmium, bismuth, 

 and tin are relatively weak. Metals with high melting-[x>ints 

 must nece.s.sarily be coherent and tenacious, because much heat is 

 rccjuired to drive their molecules apart in reducing them lo ihe 

 li({uid mobile slate in which the molecules have very small ct>- 

 hercnce ; an<l therefore at ordinary temperatures much force 

 must be applied to overcome the cohesion of the molecules and 

 break the mass. Conversely, in metals with low- melting-points 

 a small elevation of temperature will overcome the molecular 

 cohesion, and reiuler them liquid — that is. will melt them. Such 

 metals will be weak, the author continued, because if little heat 

 is required to melt the metal, less force will be needed to tear it 

 apart. Hence melting-point and tenacity are clearly connected. 

 The absolute temperature of the melting-point of a metal must be 

 clo.sely connected with its atomic volume, because the former is 

 inversely proportional to the rate at which the amplitufle of the 

 oscillations <^f the molecules increases with temperature; and the 

 rate of increase of amplitude at any given lemperalure is obtained 

 by multiplying the orclinary thermal coeflicient of linear e.\pan- 

 .si<jn by the cube root of the atomic volume. ' 



Prof. Roberts- Austen here pointed out that the recent work of 

 i Dewar and Fleming (Philosophical Magazine, vol. xxxiv. 1892. 

 ]>. 326) bears directly on this tpiestion. They employed ver\' 

 low temperatures, and show that at the aljsolute zero of tempera- 

 ture pure metals would prohalily offer no resistance to the parage 

 of an electric current, but ihal the electrical resistance of alloys 

 does not diminish so rapidly w ith the lowering of temperature 

 as in the case of pure metals. Prof. Dewar (Proceedings of the 

 Royal Institution, vol. .\iv. part 2, 1895, P ') ''^^ shown, more- 

 over, that the tenacity of pure metals anil alloys is greatly 

 ' increased by extreme cold — that is', by the closer approximation 

 ' of their molecules ; and this affords additional e\-idence that 

 1 metals become stronger at teniperatures w hich aire further and 

 ' further removed from their melting-poiiits. ' 



The disciLssion on this pa|H:r was of a .somewhat brief n.ature. 

 the reading of the report and the ■ appendices, together with the 

 carrying out of certain experiments and illustrations, taking a 

 considerable time. Mr. VVrightson also explained at some 

 length his welding experiments, which, as staled, have been 

 placed before the Royal Society. 



I'rof. tJoodman, of Leeds, gave some interesting ])articulars of 

 the work upon which he has been engaged during the last two 

 years in connection with anti-friction alloys. He had discovered 

 that these substances must always contain a metal of high atomic 

 volume, and there seemed to be a direct connection between the 

 efficiency of Ihe anti-friction of alloy and the atomic volume of 

 one of its constituents. If the atomic volume of the alloy were 

 small, then the friction was enormously incre'aseil, but with high 

 atomic volume it was reduced. He had produced an anti-friction 

 metal which would withstand a pressure of two tons to the square 

 inch when running at 550 revolutions per minute, the temperature 

 lieing 140 : that was a very remarkable result for a white metal. 

 The alloy used had a higher atomic volume than bismuth, but he 

 was not at liberty then to slate the nature of the subst.ance. He 

 wished, however, to impress the necessity of absolute purity, or 

 that if there were any impurities, they should lie of high atomic 

 volume. 



Mr. Blount, in referring lo the author's remark.s on the electro- 

 lysis of gla,ss, and the fact that ixjtassium' wiiuld not follow 

 sodium and lithium, said he would be glad of an explanation 

 why gold, which had a lower atomic volume than sodium, should 

 not have traversed the " gtilleries" left in the gla-ss by the 

 sodium. 



The summer meeting of the Institution will lie held in 

 idasgow. commencing Tuesday, July 30. 



THE RO YAL COMMISSION ON 

 TCHF.KCVI.OSIS. 



TN July 1.S90, a Royal Commis.sion was apiioinled to inquire 



I ^ and reiv>rt " what is the eftect, if any, of fooil derived from 



I tuberculous animals on human health, and if jirejiulicial. what 



arc the circumstances and conditions with regard tothe tuber- 



