Dec. 2, 1 886] 



NA TURE 



107 



My object in leading you so far back — in discussing 

 what appears to be a very matter-of-fact subject — is to 

 point to the close connection between the early recogni- 

 tion and appreciation of colour in metals or minerals, 

 and the foundation of the science of chemistry. 



In early scientific history the seven metals known to 

 the ancients were supposed to be specially connected 

 with the seven principal planets whose names they 

 originally bore, and whose colours were reflected in the 

 metals ; thus gold resembled the sun, silver the moon, 

 while copper borrowed its red tint from the ruddy planet 

 Mars. The belief in the intimate relation between colours 

 and metals, tlie occult nature of which they shared, was 

 very persistent, and we find a seventeenth-century writer, 

 Sir John Pettus, saying^ that " painters" derive "their 

 best and most proper colours from metals whereof seven 

 are accounted the chief, produced from the seven chief 

 metals, which are influenced by the seven planets.'' A 

 survival of this feeling is suggested by a modern writer, 

 Leslie, who supposed that " when Newton attempted to 

 reckon up the rays of light decomposed by the prism, 

 and ventured to assign to them the famous number 

 seven, he w^as apparently influenced by some lurking 

 disposition towards mysticism." - 



It would be impossible for me to overrate the import- 

 ance of the colour of metals in relation to scientific 

 history, for the attempt to produce a metal with the colour 

 and properties of gold involved the most intense devotion 

 to arduous research sustained by feverish, hope, attended 

 by self-deception and elaborate fraud, such as hardly any 

 other object of human desire has developed. It led to 

 despair, to madness, and to death ; but finally, through 

 all, alchemy prepared the way for the birth of chemistry, 

 and for the true advancement of science. 



In early times, as now, gold was an extremely desirable 

 form of portable property, and its colour was, perhaps, 

 held to be the most distinctive and remarkable fact about 

 it. I may incidentally observe that the dominant idea of 

 colour in connection with the metallic currency survives in 

 the familiar phrase, " I should like to see the colour of his 

 money," which curiously expresses a desire, tempered by 

 doubt as to its fulfilment. On looking back, we find that, at 

 least from the third to the seventeenth century, the colour 

 of gold haunted the early experimenters, and induced 

 them to make the strangest sacrifices, even of life itself, 

 in the attempt to imitate, and even actually to produce, 

 the precious metal. Let us see what kind of facts were 

 known within the period I have indicated. In barbaric 

 times, hammered pieces of gold, or gold beaten into thin 

 sheets and plates, were used with coloured stones and 

 coral for personal adornment. The next step was to 

 make gold go further by gilding base metals with it, and, 

 in order to do this, the colour was for the moment sacri- 

 ficed by combining the gold with quicksilver. This was done 

 at least in the time of Vitruvius, B.C. 80, heat being used to 

 drive away, as vapour, the quicksilver which had been 

 united to the gold, leaving a thin film of precious metal 

 on the surface to be gilded. But this was possibly not 

 the first method ofgilding, for wenow know,from a papyrus 

 of about the third century ^ of our era, that lead was used 

 for this purpose. Gold, when fused with lead, entirely 

 loses its golden colour, and yet, by the application of heat 

 in air, the lead may be made to flow away as a fusible 

 oxide, leaving the precious metal on the metallic object 

 to be gilt, the base metal being as it were transmuted, 

 superficially at least, into gold. The point I want to in- 

 sist upon is that the metallic colour of the gold vanished 

 during the process as carried on by the craftsman, only to 



\ " Fkta Minor," i6?6, Appendi.x. " Essay on Metallic Words,— Colour." 

 - "Treatises tin Various Subjects of Natunnl and Chemical Philosophy." 

 3_ " Les Origines de rAlchimie," par M. Berthelot, 1885, pp. 82, 89. It 

 is^ interesting to compare the account of this method of gilding by lead 

 with the e.\pression used by Homer, who says: '*.\s when g'Ad \% fttscd 

 around the silver by an experienced^ man." — "Odyssey," vi. 232-35, quoted 

 by Schliemann, '* Ilios," p. 258, in relation to a gilded knife of copper 

 which he permitted me to analyse in 1878. 



re-appear at the end of the operation ; and I am satisfied 

 that it was from such simple technical work as this that 

 the early chemists were led to think that the actual pro- 

 duction of gold — the transformation of base metals into 

 gold — was possible. The more observant of them, from 

 Geber, the great Arabian chemist of the seventh 

 centur)-, to our own countryman, Roger Bacon, in the 

 thirteenth, saw how minute a quantity of certain sub- 

 stances would destroy the red colour of copper, or the 

 yellow colour of gold. A trace of arsenic will cause the 

 red colour of copper to disappear ; therefore, the alche- 

 mists very generally argued, some small quantity of the 

 right agent, if only they could find it, will turn a base 

 metal to the colour of gold. Look, they said, how small 

 a quantity of quicksilver will change the appearance of 

 metallic tin. Here is a bar of tin 2 feet long and I inch 

 thick, which it would be most difiicult to break, though 

 it will readily bend double. If only I rub a little quick- 

 silver on its surface a remarkable effect will be produced, 

 the fluid metal will penetrate the solid one,' and in a 

 few seconds the bar will, as you see, break readily, the 

 fractured surface being white, like silver. It was by such 

 facts as this that men were led to believe that the white 

 metal, silver, could be made. 



Successive workers at different periods held divergent 

 views as to the efficacy of the transmuting agent. Roger 

 Bacon, in the thirteenth century, held that one part of 

 the precious substance would suffice to turn a million 

 parts of base metal into gold. Basil Valentine, in the 

 fourteenth century, would have been content with the 

 transmutation of seventy parts of base metal by one part 

 of the agent. While, coming to the end of the eighteenth 

 century. Dr. J. Price, F.R.S., of Guildford, only claimed 

 that the substance he possessed would transmute from 

 thirty to sixty parts of base metal. '^ 



It is a curious fact that no one seems to have actually 

 prepared the transmuting agent for himself, but to have 

 received it in a mysterious way from " a stranger " ; but I 

 must not dwell on this. I will merely point out how per- 

 sistent was the view as to the singular efficacy of the 

 transmuting agent, and I will content myself with a 

 reference to Robert Boyle, our great countryman, an 

 accurate chemist of the seventeenth century, who did 

 more than any one else to refute the errors of alchemy. 

 He nevertheless characteristically records '^ the following 

 experiment, in which, instead of ennobling a base metal, 

 he apparently degraded gold to a base one. He first 

 purified a small quantity of gold, about " two drachms," 

 with great care, and, he states, " I put to it a small 

 quantity of powder communicated to me by a stranger," 

 — it is singular that even he should have received the 

 transmuting agent in the usual way, — " and," he adds, 

 " continuing the metal a quarter of an hour on the fire, 

 that the powder might diffuse itself through it, . . . the 

 metal when cold appeared to be a lump of dirty colour; 

 . . . 'twas brittle, and, being worked with a hammer, it 

 flew into several pieces. From hence," he adds, " it 

 appears tliat an operation almost as strange as that 

 called 'projection'" (or transmutation) " may safely be 

 admitted, since this experiment shows that gold, . . . 

 the least mutable of metals, may in a short time be 

 exceedingly changed ... by so small a portion of 

 matter that the powder transmuted a thousand times its 

 weight of gold." He elsewhere observes of a similar 

 experiment, " transmutation is nevertheless real for not 

 being gainful, and it is no small matter to remove the 

 bounds which Nature seems very industriously to have 

 set to the alterations of bodies."'' The change in the 



^ Homberg, Mhtt. de I' Acad. Royale des Sciences, i7r3 (vol. published 

 1739), p. 306. 



^ " An Account of some Experiments on Mercury, Silver, and Gold made 

 at Guildford, in the Laboratory of James Price, M.D., F.R.S.," Oxford, 

 1782. 



3 " The Philosophical Works of the Hon. Robert Boyle " (Shaw's second 

 edition). 1738, vol. i. p. 78. 



4 Idid. p. 262. 



