Newton's '31st Query' and the Degradation of Gold

Newton's "31st Query" and the Degradation of Gold Thomas S. Kuhn Isis, Vol. 42, No. 4. (Dec., 1951), pp. 296-298. Stable URL: http://links.jstor.org/sici?sici=0021-1753%28195112%2942%3A4%3C296%3AN%22QATD%3E2.0.CO%3B2-F Isis is currently published by The University of Chicago Press.

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296

Desmond Reilly

bold enough to say that chemistry is not capable of making the change from the year 1900 to the year 2 0 0 0 even greater and more significant than that witnessed in the century before? The first half of this, our century, shows at least very good grounds for optimism in that regard.

Newton's "31st Query"

and the Degradation of Gold

BY THOMAS S. KUHN *

I

N the "31st Query" of the Opticks Newton suggests a corpuscular mechanism to explain the selective affinity of aqua fortis for silver and of aqua regia for gold.' His hypothesis is ingenious and, considered out of context, unexceptionable. But the text of his proposal, as printed within the "31st Query,)' presents difficulties suggesting that a significantly different phrasing may originally have been intended. The remarks to follow will outline two incongruities of the printed text, suggest a hypothetical reconstruction, and examine the relation of the emended mechanism to other portions of Newton's chemistry. In the absence of manuscript evidence the conclusions remain conjectures. But the significance of the passage may justify conjecture, for the reconstruction, if sound, illuminates Newton's otherwise obscure view of the difficulties inherent in the multiplication or degradation of gold. To the second (1717) edition of the Opticks Newton appended the inquiry: When Aqua fortis dissolves silver and not gold, and Aqua regia dissolves gold and not silver; may it not be said, that Aqua fortis is subtile enough to penetrate gold as well as silver, but wants the Attractive force to give it entrance; and that Aqua regia is subtile enough to penetrate

tive force to give it entrance? For Aqua reg& is nothing else than Aqua fortis mixed with some spirit of salt, or with sal-armoniac; and even common salt, dissolved in Aqua fortis, enables the menstruum to dissolve gold, though the salt be a gross b0dy.l

silver as well as gold, but wants the Attrac-

The clause printed in boldface is the source of the difficulties to be examined. Since these would be removed by a simple inversion of the sense of the clause, it seems possible that it was originally intended to read somewhat as follows: "and that Aqua regia has the Attractive force to penetrate silver as well as gold, but wants the subtility to give it entrance?"

* Harvard University. 'The invulnerability of gold to aqua fortis is the basis of one of the many processes listed by Agricola for the separation of gold from silver and the base metals (De re metallica, Book X ) . Agricola's American editors, H. C. & L. H. Hoover, find the earliest clear statement of this use of the acid in Geber (ibid., pp. 458-461, note). Agricola does not distinguish the actions of aqua fortis from those of aqua regia, but by the seventeenth century Boyle mentions, as though it were common knowledge, that aqua regia will attack gold and not silver (Works, edited by T. Birch [London: 17441, vol. IV, p. 287). Boerhaave employs the invulnerability of silver to aqua regia as a test to distinguish the two menstrua (Shaw's

translation of Boerhaave's Elementa Chemiae [3rd ed., London: 17531, vol. I, p. 452). The problem presented by the failure of the stronger menstruum, aqua regia, to attack silver n a y have been posed for Newton by Bacon's Novum Organum; the 28th Instance of the X I 1 Aphorism of Book I1 describes the selective affinities of the two ntenstrz~a,and Bacon's text parallels Newton's in both phraseology and context. 'S. Horsley, Isaaci Newtoni opera quae exstant omnia (London: 1782), vol. IV, p. 247. The passage occurs in substantially identical form in the second, third, and fourth English editions of the Opticks, and in Clarke's Latin translations of 1719 and 1740.

Newton's "jzst Query" and the Degradation of Gold

297

The text as printed postulates that the addition of spirit of salt, sal-armoniac, or common salt to aqita fortis reverses the relative strengths of attraction of the acid particles for the particles of silver and gold: before the addition of salt the menstruum attracts silver more strongly than gold; after the addition it attracts gold more strongly than silver. But this is unlikely to have been Newton's theory, since it conflicts with his remarks on the metalline replacement series printed within the ('31st Query" immediately before the quoted passage. Newton had stated (Horsley, 4, p. 246) that the metals could be ranged in a series ordered by their relative attraction for the particles of menstrua. The particles of iron attract those of menstrua most strongly and head the list; copper falls somewhere below iron, and mercury is still lower; tin and lead are above mercury, and silver below copper. Presumably Newton placed gold (not considered explicitly in the passage on the replacement series) below silver, for he stated in the passage quoted above that the particles of silver and aqua fortis attract each other more strongly than do those of aqua fortis and gold. By these tokens, if aqua regia is enough more forceful than aqua fortis to enter gold, it ought also possess the force necessary to enter silver, and this is incompatible with the text in boldface above. The failure of aqua regia to dissolve silver could be consistently explained by the excessive size of the particles of aqua regia which would prevent their penetrating silver, and the form of Newton's discussion makes it plausible that he in fact had some such size-dependent mechanism in mind. Why else did he introduce the role of size into the discussion? In particular, why did he emphasize that the salt added to transform aqua fortis into a solvent for gold is "gross"? Elsewhere in the "31st Query" (Horsley, 4, p. 249 f.) and in the De natura acidorum (Horsley, 4, p. 398)) Newton had remarked that salt particles are compounded of earth intimately and stably united with acid (the acid swims on the surface of the massive earth corpuscle as the ocean on the earth). Particles of earth (and hence of salt) were, for Newton, very much larger than those of acid (Horsley, 4, p. 397). So particles of the more forceful menstruum, aqua regia, containing additional acid imbibed from the salt, were presumably larger than the corpuscles of their parent aqua fortis. But what is the relevance of the grossness of the salt unless relative size enters essentially into the mechanism discussed? Newton did consider size relevant to the activity of the solvents of metals. The hypothetical "grossness" of the particles of the menstruum was the basis of his criticism of Boyle's "incalescence" experiment: and it may have been the source of his scepticism about the possibility of multiplying or degrading gold. In a letter to Oldenburg (1676) Newton suggested that Boyle had been mistaken in expecting "any great excellence in such a V , either for medical or chemical operations." Newton supposed instead that the unusual heat generated by the solution of gold in Boyle's "prepared" mercury (the menstruum) is due not to an unusually intimate penetration of the gold by the menstruum but to the "grossness" of the "metalline" particles (Newton explicitly compares them to saline particles in aqua fortis) with which the mercury is impregnated during its preparation. These particles, Newton believed, being "grosser" than those of ordinary mercury cannot mingle so intimately with gold, but they do "shake the dissolved particles more strongly'' and so engender excess heat. Thus, according to Newton, the heat generated should not be regarded as a prelude to multiplication, since, he implies, the grossness of the particles of the new menstruum prohibit their intimate penetration of the gold. The letter to Oldenburg delineates a mechanism which may once have been explicit in the "31st Query"; and, in the letter, the mechanism is coupled with an expression of the scepticism toward demonstrations of the mutability of gold which Newton

'Boyle, op. kt., vol. 111, pp. 557-564.

' Ibid., vol. I, pp. 65-66.

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Thomas S. Kuhn

..

seems devoiced repeatedly in later life. Although he believed that "Nature . lighted with transmutations" (Horsley, 4, p. 241)~Newton made an apparent exception for gold in the uniformity of possible mutations and degradations. He wrote . [the multiplication of gold], which Locke that there is "one argument against I could never find an answer to," and in the De natura acidorum he expressed the same doubts more dogmatically by coupling "omnia in aquam reduci possunt" (Horsley, 4, p. 398) with the following remarks about gold:

..

Aurum particulas habet se mutuo trahentes; harum summa vocentur primae compositionis; harum summarum summae, secundae, &c. Potest Mercurius, potest Aqua Regis poros pervadere, qui particulas ultimae compositionis interjacent, at non alios. Si posset menstruum

alios illos pewadere, vel si auri partes primae & secundae compositionis possent separari, fieret aurum fluidum & malleabile. Si aurum fermentescere posset, in aliud quodvis corpus posset transformari. (Horsley, 4, p. 399 f.)

Newton never published an explicit theoretical explanation of his doubts of the existence of a menstruum which would "ferment" gold by penetrating the "partes primae compositionis." But his scepticism can be explained, together with the textual puzzle discussed above, by supposing that Newton considered gold, lying a t the bottom of the replacement series, to have so small an attraction for menstrua that only the most powerful possessed the force necessary to dissolve it, and that such menstrua (e.g., mercury and aqua regia) being compounded with particles of earth were too "gross" to separate more than the "particulas ultimae compositionis." In sum, the " ~ 1 s tQuery" of the Opticks and the letter to Oldenburg indicate that Newton considered size as well as attractive force to be relevant to determining the power of menstrua. The fact that Newton introduced the role of size in considering the dissolution of gold but not of other metals suggests that it may have been the source of his doubts about the possibility of degrading or multiplying gold, and the nature of the mechanism prohibiting such mutations is implicit in Newton's criticism of Boyle and in the De natura acidorum. Such a size-dependent mechanism may originally have been described explicitly in the Opticks, for a relatively minor change in one of two parallel clauses of the "31st Query" would provide a clear statement of the mechanism and would simultaneously remove intrinsic difficulties in the printed text of that "Query." The conjecture that there is a corruption in the printed version of the "31st Query" derives entirely from an examination of the sense of the text. I shall be indebted to any reader who can supply either relevant manuscript evidence or an alternate explanation of the difficulties in the passage. Meanwhile it may be noted that the parallelism of the clause in boldface with the clause immediately preceding it could easily account for the origin of the postulated corruption during transcription from some draft or during type-setting. That the clause in question was actually omitted from the French translations of 1720 and 1787 must be an index either of the ease with which the parallel clauses can be miscopied or of recognition of the difficulties in the existing text. 'P. King, The Life of John Locke (London: 18301, vol. I, p. 413.