with great exactness. They afforded me satisfaction, however, in all my investigations; and people will often split a hair where it is not in the least necessary.
31. Continuation of the Experiment mentioned in § 29 ...
Anyone might object and say that the air obtained according to § 29 is perhaps nothing else than a dry acid of nitre converted into elastic vapours. But if this opinion had any foundation, this air should not only be corrosive, but should also produce nitre anew with alkalies. This, however, does not occur. Nevertheless, this objection would possess considerable weight were I not able to prove that several substances produce the same air as the acid of nitre does during distillation. But proof of this is not wanting.
I have proved in a treatise on manganese, which is to be found in the Transactions of the Royal Swedish Academy of Sciences for the year 1774, that this mineral is not soluble in any acid unless an inflammable substance be added, which communicates the phlogiston to the manganese, and by this means effects an entrance of the latter into the acids. I have shown in the same place that vitriolic acid, nevertheless, during a strong distillation with powdered manganese, unites with it and makes it soluble in water; and if this manganese is separated again from the vitriolic acid by means of precipitating agents, there are found in it the most distinct traces of the inflammable substance.... I had already observed a few years ago, that if in the calcination of manganese with oil of vitriol in an open crucible, some coal dust was driven by the current of air over the surface of this mixture, these fine coals took fire in the same instant with very great brilliancy. I accordingly made the following experiments.
32. First Experiment.—I mixed so much con
centrated oil of vitriol with finely powdered manganese that it became a stiff magma. I distilled this mixture from a small retort on the open fire. In place of a receiver I made use of a bladder, empty of air, and, in order that the vapours which might pass over should not attack the bladder, I poured into it some milk of lime (§ 30, letter b). As soon as the bottom of the retort became red hot, an air passed over which gradually expanded the bladder. This air had all the properties of a pure fire-air.
33. Second Experiment.—When I distilled two parts of finely pulverised manganese with one part of the phosphorous acid of urine in the same way as is indicated in the preceding paragraph, I likewise obtained fire-air.
34. Third Experiment.—(a.) I dissolved in aqua fortis the white magnesia employed in medicine; I evaporated this solution to dryness. I then placed the salt in a small retort for distillation, as is described in § 32. Even before the retort was red hot the acid of nitre separated from the magnesia, and that in blood-red vapours; and at the same moment the bladder began to expand. The air thus obtained was my fire-air.
It is thus seen constantly that the acid of nitre goes off again blood-red when separated by means of heat from the metals which had been dissolved in this menstruum.
(b.) I distilled mercurial nitre in the foregoing manner until the acid of nitre had separated from the residual red precipitate. In this case also I obtained our fire-air.... Whence comes the boiling of nitre, fused in a crucible and obscurely red-hot? Neither smoke nor vapours are seen to rise from it, and yet coal dust flying above the open crucible takes fire, burning brilliantly. Whence comes it that such nitre maintained in red-hot fusion in a glass retort for half an hour, becomes moist in open air and deliquesces after cooling, and still