Excerpted from De congelatione lapidum

These material bodies are divided into four species: into stones, liquifying agents, sulphurs, and salts. Of these, some have a rarefied substance and a weak compound, some others are strong substances, some are easily bent and some are not. And of those that are weak substances, some are salts that are liquefied easily by moisture, such as calcium, alum and sal armonicaum (probably ammonium chloride). And some are oily and are not easily liquefied by moisture alone, such as sulphur and auripigmentum (probably arsenic trisulphide). …And the matter of things that can be liquefied are strong compounds, mixed from watery substances and earthy substances, that cannot be separated from one another, such as watery substances that are frozen with cold after the application of heat while covered, an example of which is alum. Alum does not freeze on account of its oiliness and can be bent. However among mineral substances, rocks though materially on water, are not solidified by water alone, rather also by a dryness that alters their watery nature making it earthy, and their human is not too, and thus cannot be bent.

original latin

Alumen autem et sal armoniacum sunt de genere salis nisi quia igne inanimato magis quam terrea, unde et totum sublimatur et ipsum est aqua cum admiscetur fumus calidus fumo subtili multo igneitati est coagulatum ex siccitate. Aquaitas vero sulphureorum mixta est cum terra forti commixtione confeccione caloris donec facta sunt unctuosa et postea coagulata ex frigore. Attramenta vero composita sunt cum sale et sulphure et ex lapidibus et est in eis vis aliquorum corporum liquabilium.

Quod autem accepit vim ferream erit rubeum et croceum ut calcar. Quod vero vim aeream accepit erit viride, unde impossibile est artificialiter ista duo fieri. Argentum vivum vero ut aqua commiscetur cum terra nimium subtili sulphurea mixtione forti ne quiescat in superficie plana, et hoc est ex siccitate magna que inest illi et ideo non adheret tangenti est quod albedo eius ex claritate illius aque, et ex albedine terre subtilis que est in eo, et eciam admixtione aeris cum eo.

Et si fuerit sulphur nitidum optimum cum rubore clarum et fuerit in eo vis igneitatis simplicis non urentis, erit res optima quam recipere possunt alkimiste ut ex eo fiat aurum. Hoc enim ipsum convertit, et si fuerit argentum vivum bonum et bone substancie et sulphur non purum quod non sit in eo vis adurens convertet ipsum in aes.

Et artifices gelationem fere simile artificialiter faciunt quamvis artificialia non eodem modo sunt quo naturalia nec tam certa licet propinqua sint similia, et ideo creditur quod compositio eius naturalis hoc modo sit vel vicina huic, sed ars est debilior quam natura et non consequitur eam quamvis multum laborat.

Quare sciant artifices alkimie species metallorum mutare non posse, sed similia facere possunt et tingere rubeum citrino ut videatur aurum aut tingere albo donec sit multum simile argento aut aeri aut plumbi immundicias abstergere possunt verum tamen semper erit plumbum quamquam videature argentum optinebunt tamen in eo aliene qualitatis.