A Person any Thing vers’d in the Writings of Chymists cannot but Discern by their obscure, Ambiguous, and almost Ænigmatical Way of expressing what t… - Robert Boyle

I consider, that as generally as Chymists are wont to appeal to Experience, and as confidently as they use to instance the several substances separated by the Fire from a Mixt Body, as a sufficient proof of their being its component Elements: Yet those differing Substances are many of them farr enough from Elementary simplicity, and may be yet look'd upon as mixt Bodies, most of them also retaining, somewhat... of the Nature of those Concretes whence they were forc'd.

I remember, that being once at Leyden, I was brought to the top of a tower, where, in a darkened room (such as is now used in many places to bring in the species of external object) a convex glass, applied to the only hole, by which light was permitted to enter, did project upon a large white sheet of paper, held at a just distance from it, a lively representation of divers of the chief buildings in the town; all which, upon the admission of more light into the room, by opening the window, did immediately disappear, And methinks... that in divers of the philosophical theories, that have been formerly applauded, something not unlike this may be easily observed. for though, whilst they are looked on with such a weak and determinate degree of light, they may appear very artificial and well-proportioned fabrics, yet they appear so but in that twilight, as it were, which is requisite to their conspicuousness. For if but a full light of new experiments and observations be freely let in upon them, the beauty of those (delightful, but fantastical) structures does immediately vanish.

I need not tell you, what complaints the more candid and judicious of the Chymists themselves are wont to make of those boasters, that confidently pretend, that they have extracted the salt or sulphur of quicksilver, when they have disguised it by additaments, wherewith it resembles the concretes, whose names are given it; whereas by a skilful and rigid examen, it may be easily enough stripped of its disguises, and made to appear again in the pristine form of running mercury. The pretended salts and sulphurs being so far from being elementary parts extracted out of the body of mercury, that they are rather... de-compound bodies, made up of the whole metal and the menstruum, or other additaments employed to disguise it.