There are some mixt bodies, from which it has not been yet made appear, that any degree of fire can separate either salt, or sulphur, or mercury, muc… - Robert Boyle

I fear that the chief Reason why Chymists have written so obscurely of their three Principles, may be, That not having Clear and Distinct Notions of them themselves, they cannot write otherwise then Confusedly of what they but Confusedly Apprehend. Not to say that divers of them, being Conscious to the Invalidity of their Doctrine, might well enough discerne that they could scarce keep themselves from being confuted, but by keeping themselves from being clearly understood.

And truly... if men could be persuaded to mind more the advancement of natural philosophy than that of their own reputations, it were not, methinks, very uneasy to make them sensible, that one of the considerablest services, that they could do mankind, were to set themselves diligently and industriously to make experiments and collect observations, without being over-forward to establish principles and axioms, believing it uneasy to erect such theories, as are capable to explicate all the phænomena of nature, before they have been able to take notice of the tenth part of those phænomena, that are to be explicated.

And therefore I think you have done very wisely to make it your business to consider the Phœnomena relating to the present question, which have been afforded by experiments, especially since it might seem injurious to our senses, by whose mediation we acquire so much of the knowledge we have of things corporal, to have recourse to far-fetched and abstracted Ratiocination, to know what are the sensible ingredients of those sensible things that we daily see and handle, and are supposed to have the liberty to untwist (if I may so speak) into the primitive bodies they consist of.