the experiment; and putting one measure of nitrous air to two measures of this air, I found not only that it was diminished, but that it was diminished quite as much as common air, and that the redness of the mixture was likewise equal to that of a similar mixture of nitrous and common air.
After this I had no doubt but that the air from mercurius calcinatus was fit for respiration, and that it Lad all the other properties of genuine common air. But I did not take notice of what I might have observed, if I had not been so fully possessed by the notion of there being no air better than common air. that the redness was really deeper, and the diminution something greater than common air would have admitted.
Moreover, this advance in the way of truth, in reality, threw me back into error, making me give up the hypothesis I had first formed, viz., that the mercurius calcinatus had extracted spirit of nitre from the air; for I now concluded that all the constituent parts of the air were equally and in their proper proportion imbibed in the preparation of this substance, and also in the process of making red lead. For at the same time that I made the above mentioned experiment on the air from mercurius calcinatus, 1 likewise observed that the air which I had extracted from red lead, after the fixed air was washed out of it. was of the same nature, being diminished by nitrous air like common air: but, at the same time, I was puzzled to find that air from the red precipitate was diminished in the same manner, though the process for making this substance is quite different from that of making the two others. But to this circumstance 1 happened not to give much attention.
I wish my reader be not quite tired with the frequent repetition of the word surprize, and others of similar import; but I must go on in that 6tyle a little longer. For the next day I was more surprized than ever I had been before with finding that after the above mentioned mixture of nitrous air and the air from mercurius calcinatus had stood all night (in which time the whole diminution must have taken place, and, consequently, had it been common air it must have been made perfectly noxious and entirely unfit for respiration or inflammation) a candle burned in it and even better than in common air.
I cannot at this distance of time recollect what it was that I had in view in making this experiment; but I know I had no expectation of the real issue of it. Having acquired a considerable degree of readiness in making experiments of this kind, a very slight and evanescent motive would be sufficient to induce me to do it. If, however, I had not happened, for some other purpose, to have had a lighted candle before me I should probably never have made the trial, and the whole train of my future experiments relating to this kind of air might have been prevented.
Still, however, having no conception of the real cause of this
