When Nitre touches any substance containing a Phlogiston, and actually ignited, that is, actually on fire, it bursts out into a flame, burns, and is decompounded with much noise. In this deflagration the Acid is dissipated, and totally separated from the Alkali, which now remains by itself. Indeed the Acid, at least the greatest part of it, is by this means quite destroyed. The Alkali which is left when Nitre is decompounded by deflagration, is called in general _Fixed Nitre_, and, more particularly, Nitre fixed by such and such a substance as was used in the operation. But if Nitre be deflagrated with an inflammable substance containing the vitriolic Acid, as sulphur, for instance, the fixed Salt produced by the deflagration is not a pure Alkali, but retains a good deal of the vitriolic Acid, and, by combining therewith, hath now formed a neutral Salt. Hitherto Chymists have been at a loss for the reason why Nitre flames, and is decompounded in the manner above-mentioned, when it comes in contact with a Phlogiston properly circumstanced. For my part, I conjecture it to be for the same reason that vitriolated tartar is also decompounded by the addition of a Phlogiston; _viz._ the Nitrous Acid, having a greater affinity with the Phlogiston than with the fixed Alkali, naturally quits the latter to join with the former, and so produces a kind of sulphur, differing probably from the common sulphur, formed by the vitriolic Acid, in that it is combustible to such a degree, as to take fire and be consumed in the very moment of its production; so that it is impossible to prevent its being thus destroyed, and consequently impossible to save it. In support of this opinion let it be considered, that the concurrence of the Phlogiston is absolutely necessary to produce this deflagration, and that the matter of pure fire is altogether incapable of effecting it: for though Nitre be exposed to the most violent degree of fire, even that in the focus of the most powerful burning-glass, it will not flame; nor will that effect ever happen till the Nitre be brought into contact with a Phlogiston properly so called, that is, the matter of fire existing as a principle of some body; and it is moreover necessary that this Phlogiston be actually on fire, and agitated with the igneous motion, or else that the Nitre itself be red hot, and so penetrated with fire as to kindle any inflammable matter that touches it. This experiment, among others, helps to shew the distinction that ought to be made between pure elementary fire, and fire become a principle of bodies, to which we have given the name of Phlogiston.