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Remarks on DR. PRIESTLEY'S Experiments and Observations relating to the Analysis of Atmospherical Air, and his Considerations on the Doctrine of Phlogiston and the Decomposition of Water. By THEOPHILUS LEWIS RUPP.

The high rank of Dr. Priestley in the philosophical world entitles his writings to the greatest attention; and, it is with much diffidence I venture to lay before this society a few observations on a late publication of this gentleman, entitled "Experiments and Observations relating to the Analysis of Atmospherical Air; and Considerations on the Doctrine of Phlogiston and the Decomposition of Water."

The general arguments in support of the new chemical theory, and against the doctrine of phlogiston are so well known; and (to judge by their effect) so well understood, as to require neither repetition nor elucidation. I shall therefore confine myself to the consideration of the particular arguments contained in that publication.

The intention of the first part of it is to shew, that in every case of the diminution of atmospherical air, which the antiphlogistians ascribe to simple ab

sorption, there is emitted some substance; and that this substance is the same which has been called phlogiston.

*

That a mixture of iron-filings and sulphur with a little water (if it be continued in the air after the diminution has advanced to its maximum) occasions an increase of the quantity, by an addition of inflammable air, is easily accounted for. In this instance, as in many others of the same nature," the attraction of the iron to sulphuric acid increases the attraction of the sulphur to oxygen. That of the atmospherical air, which surrounds the mixture, is absorbed; and when this is effected, the attraction of the sulphur and iron still continuing, the water contained in the mixture is decomposed; its oxygen combines with the sulphur and iron; and its hydrogen is set at liberty. Hence the increase of bulk after the diminution has advanced to its maximum. When this mixture is confined with pure oxygenous gas, the whole of this is absorbed, and no azote presents itself after the operation. But if something were emitted, which has the property of phlogisticating† pure air, there should be found,

To these belong the production of alum from the schistus aluminaris, of sulphate of iron from martial pyrites, of nitrate of lime from lime mixed with substances containing the basis of nitrous acid, &c.

+ I ought to make an apology for the confusion of terms which occur in this paper; but I was not able to avoid making use of the terms of my antagonist, without producing greater confusion.

at the end of the process, azotic gas or phlogisticated air, exceeding in quantity the pure air, in as much as the substance emitted amounted to.

The mode in which the martial sulphuret operates on pure air, is illustrated by the operation of the calcareous and alkaline sulphurets. These also have a very strong smell, and the property of absorbing pure air. But when the diminution has arrived at its maximum, no increase of the bulk of the air ensues.* But if the diminution were effected by the emission of some substance from the sulphuret, that emission would probably go on after the diminution: at least there is as much ground for this supposition as there is for Dr. Priestley's, namely, that it is probable that something is emitted from the martial sulphuret during the diminution of the air, because something is emitted afterwards. In ali these cases, the air is diminished both in volume and in weight; and it is surely absurd to say, that this is caused by an addition of something. But the result of the following experiment will remove every doubt on this subject. I kept a mixture of iron

* I know that the contrary has been asserted by Dr.Priestley and some others; but I am convinced by my own experiments, that no increase of air takes place after the alkaline or calcareous sulphurets have absorbed the oxygen of air exposed to the action of either of them. I constantly make use of liquid sulphuret of pot-ash as a test, but I have never found the least increase of air after the greatest diminution of it had taken place.

filings sulphur and water, in a large glass bell, containing atmospherical air confined by water. The mixture and the glass vessel which contained it (which was purposely chosen large and with a long narrow neck, to prevent the moisture from evaporating), weighed, together, 1324 grains, troy. When the air was diminished thirty cubic inches, the vessel containing the mixture was taken away, made perfectly dry and weighed again. It now weighed 1333 grains, consequently nine and one fourth grains more than before the operation, which corresponds exactly enough with the weight of the air which was absorbed.

Dr. Priestley admits (p. 6), that "iron-filings and sulphur, as well as phosphorus, and most of the other substances which have been generally used for the purpose of phlogisticating atmospherical air, do likewise imbibe the dephlogisticated air contained in it, and thereby gain as much weight as the air has lost." This cannot be reconciled with his notion, that something is emitted from the ironfilings and sulphur, which has the property of phlogisticating pure air, unless we take for granted that atmospherical air contains more oxygen than what, by synthesis, we know that it contains; and even then the difficulty will recur, that pure oxygenous gas exposed to this mixture is wholly absorbed, without any residuum of azotic gas.

Dr. Priestley says, that flowers, and especially

those which have the strongest smell, phlogisticate air. But it is well known on the other hand, that aromatic plants, in particular, afford very pure oxygenous gas in great quantity. When vegetables vitiate air, it is probably owing to a beginning of putrefaction. This was the case in an experiment which Dr. Priestley relates in his third vol. of Experiments on Air, p. 278. A sprig of mint was introduced into a jar of dephlogisticated air, sometime in April. It was examined the 12th May. "The dephlogisticated air," says he, "was injured, which I attributed to the rotting of some of the leaves of the plant." I recollect only one experiment which has been made to ascertain the effect of flowers on atmospherical air. It is described in Dr. Priestley's 2d vol. of Experiments, p. 247. The air was considerably injured by a rose confined in it. It would have thrown light on the subject, if notice had been taken, whether or not the volume of the air in that experiment was diminished. At all events it is certain, that the effect was not produced by the smell or aroma of the flower, since cloves and musk, which I kept confined for a fortnight in atmospherical air over mercury, neither diminished nor vitiated it in the least.

It is flattering to the antiphlogistians, that their opponents, in the very act of opposition, are obliged to have recourse to their theory in explanation of certain phænomena, Dr. Priestley observing