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NATURE 



[April 7_,.j_892 



lower than that of the least fusible constituent. There 

 is one other fact of much interest connected with this 

 alloy. When it is treated with dilute hydrochloric acid, 

 chloride of aluminium is formed, and gold is released in 

 a singularly voluminous form. The heat of formation of 

 the gold-aluminium alloy has not been determined, but 

 hydrochloric acid, which will not attack gold, will 

 readily split up this compound, of which more than 

 three-fourths is gold ; the compound, in fact, behaves 

 like a distinct metal, having special heats of oxidation 

 and chlorination of its own. 



(3) Lastly, we come to the question of solutions of 

 metals in each other. One very remarkable instance of 

 the behaviour of metals at high temperatures reveals the 

 fact that the presence of a small amount of a metal in a 

 mass of another lowers the freezing-point of the mass. 

 In the industrial world this has long been known. 

 Cellini tells us, for instance, that when the bronze for his 

 great figure of Perseus, at Florence, was running out of 

 the furnace, it suddenly showed signs of setting, and he 

 therefore threw pewter plates and dishes into the ducts 

 through which the metal had to pass— "a thing," he 

 says, " never before done." The fluidity of the metal was 

 immediately increased, and he found every part of the 

 casting " to turn out to admiration." 



The excellent work of Heycock and Neville,^ on the 

 lowering of the freezing-points of metals, by the addi- 

 tion of other metals, should, I would suggest, form 

 the subject of a lecture in this Institution at an 

 early day. I cannot attempt to deal with the matter 

 here. In leading up to these questions of solution, 

 as applied to metals, I would remind you that Lord 

 Rayleigh told us a few evenings since that it was by 

 no means certain that a gas rushing into a vacuous globe I 

 ever completely fills it, as there may still be tiny spaces ' 

 into which " odd molecules " fail to find room to vibrate i 

 in. If it is difficult for a gas to entirely fill a vacuous 

 space, you would think it impossible for a small quantity 

 of a metal to rapidly permeate a fluid mass of another 

 metal ; nevertheless, so far as analysis can detect, this 

 does happen. 



It may be incidentally observed that the relations of 

 the ordinary gases to metals are far more intimate than 

 they were formerly supposed to be, and this was proved 

 by Graham's work on the absorption of gases by metals, 

 which has often been dealt with in this Institution. To 

 take only the case of iron, more than twenty years ago j 

 Sir Lowthian Bell showed that carbonic oxide can carry 

 away iron, which is released when the temperature 

 is raised. Ludwig Mond and Langer have since iso- 

 lated most interesting compounds of iron and carbonic 

 oxide. But to return to the solution of metals in 

 metals. 



The method of taking autographic curves of the 

 cooling of masses of metal has already been indi- 

 cated in Fig. 4,'^ and they ought to enable much 

 information to be gained as to what is taking place 

 throughout the mass. Such curves should render it 

 possible to ascertain which of the rival theories as 

 to the nature of solution, as applied to salts, is sup- 

 ported by the behaviour of a metal dissolved in a metal. 

 When, for instance, a little aluminium dissolves in gold, 

 is the analogue of a hydride formed, and, if so, is the 

 curve of freezing-points of a series of aluminium-gold 

 alloys a continuous one ? On the other hand, does the 

 theory advocated by van 't Hoff, Arrhenius, and Ostwald 

 gain support, and do the molecules of the dissolved 

 metals act independently of the solvent — that is, does 

 osmotic pressure come into play .? It will be remembered 

 that the law which regulates osmotic pressure has exactly 

 the same form as Boyle's law — that is, the pressure is 



proportional to the density of the gas or of the solution. 

 Is the view of Arrhenius correct — that, if a solution be 

 very dilute, the molecules of the dissolved substance are 

 dissociated, act independently of each other, and behave 

 like a perfect gas ? 



It will require years of patient work before these ques- 

 tions can be answered ; but it appears certain, from the 

 admirable experiments of Heycock and Neville,^ to 

 which reference has already been made, that, taking 

 metals with low melting-points (such as tin or lead) as 

 solvents, the lowering of the freezing-point of the solvent 

 is really due to the bombardment exerted by the molecules 

 of the dissolved metals. 



I have extended this investigation by employing as a 

 solvent a mass of fluid gold, which has a high melting- 

 point, and is not liable to oxidation, and the results con- 

 firm those obtained by Heycock and Neville. 



There is yet one other question : When metals are 

 added in small quantities to a metallic mass, may the 

 solvent remain inert.? Here is a mass of 1000 grammes 

 of lead, and to it 15 grammes of gold, or 1:6 atoms for 

 every 100 atoms of lead, will now be added. It could be 

 shown that the gold is readily dissolved, and remains dis- 

 solved, even if the lead be solidified. Now, to the fluid 

 lead sufficient aluminium will be added to form the 

 purple alloy with the dissolved gold ; the mass will be 

 well stirred, but the aluminium will not unite with the 

 lead ; it will nevertheless find out the gold, and, after 

 uniting with it, will carry it to the surface of the bath. 

 Thence it can be removed, and the purple colour of 

 the .alloy identified, or the gold it contains can be 

 revealed by the method Prof. Hartley - has given us for 

 detecting the presence of gold in an alloy by volatilizing 

 the alloy in a torrent of sparks from an induction coil, 

 and condensing the vapour on mica. 



The union of the aluminium and the gold must, how- 

 ever, be peculiar. Crookes-' has shown that when this 

 alloy is used as an electrode in a vacuum tube, the gold 

 is volatilized from the alloy and deposited as a film on the 

 glass, leaving the aluminium behind. 



The purple alloy presents us with' the most interesting 

 case yet known of a molecule built up of purely metallic 

 atoms, but we are certain that the atoms are still those of 

 gold and aluminium— that is, the atoms of the united 

 metals remain unchanged. The interest in this substance 

 is deepened if it be remembered that our aim at the 

 present day is the same as that of the alchemists, for we 

 are striving, as they did, to attack and change the chemist's 

 atoms themselves. We seek, as truly as they, to effect 

 the transmutations, which, as Boyle said, would " be 

 none the less real for not being gainful," and employ 

 high temperatures in the hope of simplifying the mole- 

 cular structure of metals. We no longer consider gold to 

 be the " sum of perfection," but still retain the belief ex- 

 pressed by Geber, eleven hundred years ago, that, " if we 

 •would change metals, we must needs use excess of heat." 

 A poet also appears to have felt this, for George Herbert 

 writes in the seventeenth century — 



" I know ... what the stars conspire, 

 What willing Nature speaks, what forced by fire " ; 



thus comparing the ordinary response of Nature to the 

 investigator with the evidence he elicits from her by 

 heat. 



By fusing gold, and staining it " the purple of the 

 dawn," a new interest has been given to the metal which 

 the alchemists always connected with the sun ; and for 

 further proof that metallic atoms may be changed) we 

 must turn to the sun itself, as to a great metallurgical 

 centre, where " all the elements shall melt with fervent 

 heat." 



1 Chem. Soc. Journ., vol. Iv., 1889, 

 Nvol. lix. , 1891, p. 936. 



2 Proc. Roy. Scie., vol. xlix. p. 347, 



p. 666 ; vol. Ivii., 



pp. 376, 656 ; I 



Proc. Koy. Soc, vol. xlvi., 1889, p. 

 Proc. Roy. Soc, vol. 1., 1891, p. 88. 



NO. I 171, VOL. 45] 



