The following represents my halting preliminary attempt to follow up on the unfootnoted claim that "The other side [Boyle collaborator George Starkey] refused to hear were those who dismissed alchemy as a deception, a delusion, a fantasy. Yet among scholastic philosophers these were the majority, from Aquinas and Albertus Magnus on" (David Wootton, The invention of science: a new history of the scientific revolution (New York: HarperCollins Publishers, 2015), 354-355). Below are three of the several hits on lemmas #04023, #04023e, and #04023j in Corpus Thomisticum (which is not to say that passages without these terms are irrelevant). The passage from the later Summa seems to my inexpert eye more tentative than the one from the much earlier Commentary on the Sentences. I have not read any of the scholarship on the treatise on alchemy mistakenly (?) attributed to Aquinas, or any of the scholarship on medieval alchemy.
"Demons do not operate except by the mode of art. But art cannot confer substantial form. Hence it is said in the chap[ter] on numbers, ‘proponents [(auctores)] of alchemy cannot change the substantial form.’ Therefore neither can demons produce substantial forms."
"Art cannot by its [own] power confer substantial form. This can [only] be done by the power of a natural agent, as is clear in this, that by art the [substantial] form of fire [(a natural agent)] is introduced into firewood. But there are certain substantial forms which art can in no way introduce, because it cannot devise active and passive propria, though it can produce something similar in these [substantial forms? active and passive propria?], as [when] alchemists produce something similar to gold with respect to exterior accidents, but yet do not make true gold. For the substantial form of gold is [induced] not by the heat of the fire which alchemists use, but by the heat of the sun [(a natural agent)] in [that] determinate place in which the mineral power [(a natural agent)] is vigorous. And therefore such gold lacks the operation consequent upon the species; and similarly in other things which are produced by the operation of [alchemists]."
Thomas Aquinas, Super Sent. lib. 2, d. 7, q. 3, a. 1, arg and ad 5, trans. Perisho. (I have not examined Super Sent. lib. 4, d. 11, q. 3, a. 4, qc 3, expos.) Latin from Corpus Thomisticum:
"Daemones non operantur nisi per modum artis. Sed ars non potest dare formam substantialem; unde dicitur in cap. de numeris: sciant auctores alchimiae, species transformari non posse. Ergo nec Daemones formas substantiales inducere possunt."
"ars virtute sua non potest formam substantialem conferre, quod tamen potest virtute naturalis agentis; sicut patet in hoc quod per artem inducitur forma ignis in lignis. Sed quaedam formae substantiales sunt quas nullo modo ars inducere potest, quia propria activa et passiva invenire non potest, sed in his potest aliquid simile facere; sicut alchimistae faciunt aliquid simile auro quantum ad accidentia exteriora; sed tamen non faciunt verum aurum: quia forma substantialis auri non est per calorem ignis quo utuntur alchimistae, sed per calorem solis in loco determinato, ubi viget virtus mineralis: et ideo tale aurum non habet operationem consequentem speciem; et similiter in aliis quae eorum operatione fiunt."
"Gold and silver are costly not only on account of the usefulness of the vessels and other like things made from them, but also on account of the excellence and purity of their substance. Hence if the gold or silver produced by alchemists has not the true specific nature of gold and silver, the sale thereof is fraudulent and unjust, especially as real gold and silver can produce certain results by their natural action, which the counterfeit gold and silver of alchemists cannot produce. Thus the true metal has the property of making people joyful, and is helpful medicinally against certain maladies. Moreover real gold can be employed more frequently, and lasts longer in its condition of purity than counterfeit gold. If however real gold were to be produced by alchemy, it would not be unlawful to sell it for the genuine article, for nothing prevents art from employing certain natural causes for the production of natural and true effects [(effectus)], as Augustine says (De Trin. iii, 8) of things produced by the art of the demons."
Thomas Aquinas, ST II-II.77.2.ad 1, trans. FEDP. Latin from Corpus Thomisticum:
"aurum et argentum non solum cara sunt propter utilitatem vasorum quae ex eis fabricantur, aut aliorum huiusmodi, sed etiam propter dignitatem et puritatem substantiae ipsorum. Et ideo si aurum vel argentum ab alchimicis factum veram speciem non habeat auri et argenti, est fraudulenta et iniusta venditio. Praesertim cum sint aliquae utilitates auri et argenti veri, secundum naturalem operationem ipsorum, quae non conveniunt auro per alchimiam sophisticato, sicut quod habet proprietatem laetificandi, et contra quasdam infirmitates medicinaliter iuvat. Frequentius etiam potest poni in operatione, et diutius in sua puritate permanet aurum verum quam aurum sophisticatum. Si autem per alchimiam fieret aurum verum, non esset illicitum ipsum pro vero vendere, quia nihil prohibet artem uti aliquibus naturalibus causis ad producendum naturales et veros effectus; sicut Augustinus dicit, in III de Trin., de his quae arte Daemonum fiunt."