that which I got in the middle of the process. When the air was produced very faft, it was exceedingly turbid, as if it had been filled with a white powder.

In my former publication, the reader will have seen the refult of feveral proceffes in which nitrous air was phlogisticated with iron and liver of fulphur, in confequence of which a candle would burn in it, either naturally, as in common air, or with a beautifully enlarged flame. As this air, in some respects, resembles common air, though it be noxious, it occurred. to me, that it might be poffible, by means of fome ingredients, to make it in all respects common air; and with this, and other views, I, at different times, filled feveral phials with nitrous air, putting to it iron or liver of fulphur to phlogisticate it, and also pieces of chalk, or a mixture of fixed air, in order to fupply it with that ingredient, which it is well known the atmosphere contains; and in other respects also I varied these preparations, in order to have the greater chance of fucceeding with re-: Spect to the object of the experiment. These projects, the reader will eafily imagine, were antecedent to my difcovery of the real conftitution of the atmosphere, as explained in a preçeding fection. However, as the proceffes took:

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up a good deal of time, and some persons, intent upon these purfuits, may wish to know what was the refult of them, unfuccefsful as they were with respect to my main object, I shall here recite the particulars of the principal of them, in the order in which they were made.

The reader may also have obferved, that, in one particular cafe, mentioned vol I. p. 220, a quantity of nitrous air, which had been exposed two months to fome iron nails in quickfilver, was diminished by a mixture of fresh nitrous air. This I find in my register, written at the time of obfervation, and therefore can hardly doubt but that I must have observed that appearance, which is an indication of a confiderable degree of purity in the air, and of its fitness for refpiration. But as in none of the following experiments I could get the fame appearance, I suspect that I muft, fome way or other, have deceived myself on the former occafion. It must be observed, however, that it by no means follows, that because we cannot, in a course of experiments, produce the fame appearance in what we imagine to be the fame circumstances, that we were therefore deceived with respect to the appearance itself; because nothing is more common than for perfons to be deceived with refpect to what they imagine

imagine to be the fame circumstances in an experiment.

June 4, 1774. Two quantities of nitrous air, which had ftood above four months in contact with iron in water, just extinguished a candle.

July 25. A candle burned with an enlarged flame; but not more than double, in nitrous air, which had been in contact with iron in quickfilver, about fix months. The appearance was the fame when the candle was dipped into it, both before it was once paffed through the water, and afterwards. Water being admitted to the remainder of this air, it began to be abforbed as ufual.

March 2, 1775. Nitrous air, which had been confined above a year in contact with iron, ftanding in water, was, in all refpects, like phlogisticated common air: it neither diminished common air, nor was diminished by nitrous air, and extinguished a candle. It had alfo the faint fmell of phlogisticated air. The more rufty iron is, the fafter it diminishes nitrous air, which looks as if it took phlogiston from the nitrous air, rather than communicated any to it.

March 4. In about one day, and without any heat, about one-third of a given quantity of nitrous air was imbibed by liver of fulphur. In the remainder a candle burned with an enlarged flame; but it was not at all diminished by fresh nitrous air,

March 6. Nitrous air, exposed to liver of fulphur and chalk, exhibited the fame phenomena as if no chalk had been put to it: it admitted a candle to burn in it with an enlarged flame, was not diminished by nitrous air, and extinguished a candle, after a very little agitation in water.

March 10. A quantity of one-half nitrous, and one-half fixed air, which had been in contact with iron, was reduced one-third in its dimenfions, and the remainder admitted a candle to burn in it with an enlarged flame, but was not diminished by nitrous air.

May 7. I examined feveral quantities of nitrous air, and mixtures of nitrous and fixed air, which had ftood expofed in quickfilver, to iron, or to iron that had rufted in nitrous air, about two months. None of them were diminished by nitrous air, or diminished common air. In general they extinguished a can

dle;

dle; but, in one of them, a candle burned naturally when the fixed air had been washed out! of it in water. One quantity of nitrous air, which had been exposed to iron that had rusted in nitrous air, was diminished about one-tenth, but was very little changed; for it diminished common air almost as much as fresh-made nitrous air. Another quantity of nitrous air, which had been expofed to iron-nails, diminished common air rather lefs than the preceding.