In a pretty long time I agitated nitrous air in water, supplying it from time to time with more, as the former quantity diminished, till only one eighteenth of the whole quantity remained; in which state it was so wholesome, that a mouse lived in two ounce measures of it more than ten minutes, without shewing any sign of uneasiness; so that I concluded it must have been about as good as air in which candles had burned out. After agitating it again in water, I put one part of fresh nitrous air to five parts of this air, and it was diminished one ninth part. I then agitated it a third time, and putting more nitrous air to it, it was diminished again in the same proportion, and so a fourth time; so that, by continually repeating the process, it would, I doubt not, have been all absorbed. These processes were made in lime-water, without forming any incrustation on the surface of it. Lastly, I took a quantity of common air, which had been diminished and made noxious by phlogistic processes; and when it had been agitated in water, I found that it was diminished by nitrous air, though not so much as it would have been at the first. After cleansing it a second time, it was diminished again by the same means; and, after that, a third time; and thus there can be no doubt but that, in time, the whole quantity would have disappeared. For I have never found that agitation in water, deprived of its own air, made any addition to a quantity of noxious air; though, _a priori_, it might have been imagined that, as a saturation with phlogiston diminishes air, the extraction of phlogiston would increase the bulk of it. On the contrary, agitation in water always diminished noxious air a little; indeed, if water be deprived of all its own air, it is impossible to agitate any kind of air in it without some loss. Also, when noxious air has been restored by plants, I never perceived that it gained any addition to its bulk by that means. There was no incrustation of the lime-water in the above-mentioned experiment. It is not a little remarkable, that those kinds of air which never had been common air, as inflammable air, phlogisticated nitrous air, and nitrous air itself, when rendered wholesome by agitation in water, should be more diminished by fresh nitrous air, than common air which had been made noxious, and restored by the same process; and yet, from the few trials that I have made, I could not help concluding that this is the case. In this course of experiments I was very near deceiving myself, in consequence of transferring the nitrous air which I made use of in a bladder, in the manner described, p. 15. fig. 9. so as to conclude that there was a precipitation of lime in all the above-mentioned cases, and that even nitrous air itself produced that effect. But after repeated trials, I found that there was no precipitation of lime, except, in the first diminution of common air, when the nitrous air was transferred in a glass vessel.