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most of the Experiments that we have hitherto proposed, Cold is wont to be regularly produc'd in a Mechanical way; but I shall now adde, that in some sort of Trials I found that the Event was varied by unobserv'd Circumstances; so that sometimes manifest Coldness would be produced by mixing two Bodies together, which at another time would upon their Congress disclose a manifest Heat, and sometimes again, though more rarely, would have but a very faint and remiss degree of either.

Of this sort of Experiments, whose Events I could not confidently undertake for, I found to be, the dissolution of Salt of Tartar in Spirit of Vinegar, and of some other Salts, that were not acid, in the same Menstruum, and even Spirit of Verdigrease (made per se) though a more