tity of water, equal in weight to the lofs fuftained by the feales in their revival in the form of iron, is found in the recipient. Whereas in the experiment with the red precipitate, there is certainly no more water found than may be fuppofed to have been contained in the inflammable air which difappeared, or to have been lodged without being perceived among the particies of the precipitate itself. Confequently the fcales of iron must be confidered as the calx of iron united to water, and red precipitate as mercury, united to dephlogifticated air, or rather, perhaps, as Mr. Kirwan fuppofes, to fixed air, the phlogifton belonging to which revives the mercury, while its other component part, the dephlogifticated air, is fet at liberty, forming an union with the clement of heat.

"The difficulty with refpect to what becomes of the two kinds of air, was not leffened by the attempts which I made to collect all that I could from repeated decompofitions of inflammable and dephlogifticated air in a clofe veffel.

As I had produced water in this procefs when I made no more than a single explofion at a time, I thought that by continuing to make explosions in the fame veffel, the water would not fail to accumulate, till I might collect what quantity I plea'ed; and I intenced to have collected a confiderable part of an ounce, And as I fhould know exactly what quantity of air I decompofed, I had no doubt of being able to afcertain the proportion that the water and air bore to each other.

"With this view I made a mixture of a large quantity of air, one third dephlogiticated, and twothirds inflammable from iron and

oil of vitriol. But though I had a fenfible quantity of water at the first explofion (in each of which was ufed between four and five ounce meafures of the mixture of air) I was furprised to perceive no very fenfible increafe of the quantity of water on repeating the explotions. Having, therefore, expended 48 ounce meafures of the mixture, I difcontinued the procefs; and collecting the water with all the care that I could, I found no more than three grains, when there ought to have been eleven.

"In this procefs the infide of the vefiel was always very black after each explosion, and when I poured in the mercury after the explosion, though there was nothing viable in the air within the veffel, there iffued from the mouth of it a dense capour. This was even the cafe, though I waited fo much as two minutes after any explosion before I proceeded to put in more mercury in order to make another; which if the vapour had been steam, would have been time more than fufficient to permit it to condense into water. I even perceived this vapour when I had a quantity of water in the veffel, and the explo fion was confequently made over it, as well as in contact with the fides of the veffel which were wetted with it; fo that as this vapour had paffed through the whole body of water when the veffel was inverted, it is probable that it must have confifted of fomething elfe than mere water. But I was never able to collect any quantity of it, though it must have been fomething produced by the union of the two kinds of air.

In order to collect a quantity of the matter that formed this vapour, I contrived the following apparatus. In a cork with which

I could fhut the orifice of the ftrong glafs veffel in which the explosions were made, I had two perforations. Through one of these I poured the mercury, by means of a glafs funnel; but into the other was introduced a glass tube, which, being bended, was inferted, by means of a cork, into a thin glafs veffel, and went almost to the bottom of it. A fmall hole was alfo made in the cork, to permit the air to go out. Confequently, all the air that remained in the frong glafs veffel, with whatever vapour it might contain, muft, as I poured in the mercury, neceffarily pass through the glafs tube, and be diffufed through the thin glafs vefiel; in which I imagined that all its contents, fluid or folid, muft be depofited. However, though I repeated the experiment feveral times with this apparatus, making about twenty explotions in each, I could not find any depofit in the veffel, befides a fmall quantity of water; which, added to the water collected in the strong veffel, came far fhort of the weight of the air that was decompofed.

All the conjecture that I can advance, in order to explain this phænomenon, is that, fince foot yields pure air, as will appear in the course of this volume, part of the foot is formed by the union of the dephlogisticated air in the atmofphere and the inflammable air of the fuel. But Smoke, which contins much foot, is foon difperfed, and becomes invitible in the open air. Such, therefore, may be the cafe here. The foot formed by the union of the two kinds of air may be diffufed through the air, in the vetfel in which they are exploded, and be carried invifibly into the common atmosphere, which may account for my not being able

to collect any quantity of it in this apparatus.

66

Hoping to fucceed better in collecting this volatile matter by means of a quantity of water in cumbent upon the mercury, in the ftrong glais veffel in which the explofions were made (though I had found that part of it could efcape through the water) I decom. pofed a great quantity of the two kinds of air in thefe circumftances; and prefently found that the water became very cloudy, and was at length full of a blackish matter. This I collected, and found that it remained perfectly black upon the earthen veffel in which the water containing it was evaporated; which would not have been the cafe if the blackish matter in the water had been that powder of mercury, which is produced by agitating it in pure water. For that black mass always became white running mercury the moment the water was evaporated from it. Could I have collected a fufficient quantity of this black matter, I might have fatisfied mytelf whether it was a proper foot or not.

Mr. Warltire first obferved this cloudinefs in a veffel in which he burned inflammable air; but it is temarkable that fometimes I got it repeatedly in thefe explosions, all the infide of the veffel becoming quite black after the explosion; and at other times I have not been able to get this appearance at all; fo that I am not yet able to determine on what it depends. At one time, having the infide of the ftrong glafs tube made very black with thefe explofions, I let it remain a day or two expofed to the common air, when the blacknets difappeared, leaving the infide of the veffel covered with small globules of white mercury. it feems, there

fore,

fore, that part of the phlogiston of the inflammable air fometimes attaches itself to the vapour of mercury, diffufed invifibly through the fpace within the veffel, and that it quits it to unite to the air of the atmosphere.

"That water in great quantities is fometimes produced from burning inflammable and dephlogitti. cated air is evident from the experiments of Mr. Cavendish and Mr. Lavoisier. I have alfo frequently collected confiderable quantities of water in this way, though never quite fo much as the weight of the two kinds of air decompof ed. My apparatus for this purpofe was the following Into the mouth of a large glafs balloon I introduced a tube from the orifice of which there continually iffued inflammable air, from a veffel containing iron and oil of vitriol This being lighted, continued to burn like a candle. Prefently after the lighting of it, the inside of the bailoon always became cloudy, and the moisture foon gathered in drops, and fettled in the lower part of the balloon. To catch what might iffue in the form of vapour, in the current of air through the balloon, I placed the glafs tube in which I always found fome water condenfed. It is very poffible, however, that in both thefe modes of experimenting, the water may be converted into a kind of vapour, which is very different from feam, and capable of being conveyed a great way through air, or even water, without condensation, along with the air with which it is mixed; and on this account it may not be poffible, in either of thefe modes of experimenting, to collect all the water into which the two kinds of air may be converted. The nature of this kind of vapour into which

water may be changed, and which is not readily condenfed by cold, is very little understood, but well deferves the particular attention of philofophers. Even mercury will evaporate, fo as to lofe weight, in a degree of heat below that of boiling water.

"That the water collected in the balloon comes from the decompo fition of the air, and not from the fresh air circulating through it, was evident from placing balls of hot iron in the place of the flame, and finding that, though the balloon was as much heated by them as by the flame of the burning of the inflammable air, and confequently there must have been the fame current of the external air through it, no moisture was found in the balloon.

"When in this manner, I burned inflammable air from pure iron, the water I collected was perfectly free from acid, and the infide of the balloon was quite clear, but when I ufed fulphurated iron, there was a denfe white cloud that filled the infide of the balloon. There was alfo a strong fmell of vitriolic acid air, and the water collected was fenfibly acid to the taste.

"Having found that water is an effential ingredient in the conftitution of inflammable air, at least as produced from iron, it fill remained to be determined whether, when a calx is revived, and the metal formed, the pure phlogiston only entered the calx, or, together with it, that water which was neceffary to its form of inflammable air.

"In order to afcertain this, I frequently revived dry calces of lead in dry inflammable air, and examined the appearances of moifture afterwards. But notwithstanding all the attention that I gave

to the process, I could not be abfolutely certain, whether more moisture was left in the veffel, than might have exifted extrancoufly in the inflammable air, or whether, when the phlogifton was abforbed, it left behind it any water that had been effential to it, as inflammable air. Appearances were fuch as fometimes inclined me to think that every thing which constitutes inflammable air goes into a calx, in order to form the metal; fo that if this, though a compound thing, be called phlogifton, it will fill be true that phlogiton and inflammable air are the fame thing; but, on the whole, I rather think that the water which was effential to the conftitution of inflammable air was left behind.

"That water, however, may exist in bodies in a combined fiate, without appearing to be water, we know in many cafes; but it is in nothing more evident than in the fcales of iron, than which no fubtance can have lefs the appearance of containing water.

"But not to give a mere opinion, I fhall recite the particulars of a few experiments, which I made with the view above-mentioned. In 6 ounce measures of inflammable air from irou, I revived lead till it was reduced to 1 ounce meafure, care having been taken to make every thing as dry as poffible. Some moisture, however, did appear, perhaps more than half a grain ; but as this air had been confined by water, it was no more than might have been contained in it as an extraneous fubflance. It ought alfo to be confidered that it must be exceedingly difficult to expel all moisture by mere heat from fuch a powdery fubftance as the yellow alx of lead, without reviving the

metal.

All chemis well know how firmly moisture adheres to many fubilances, with which it does not properly unite, and how much heat is neceffary to feparate them.

"Again in 6 ounce measures of inflammable air from iron, I revived lead till there remained 0,9 of a measure, and there was hardly any more moisture than I had rea fon to think might have been in the veffel, independently of what was contained in the inflammable air; and in order to enable myself to judge of this, I melted an equal quantity of the fame minium, under a dry glafs veffel with common air, when a little moisture appeared, on the infide of the glafs, about as much, I thought (for I could only judge by my eye) as when I had revived the lead from that minium in inflammable air. The quantity of lead revived was only 16 grains, but a good deal of the minium had been made black in the process.

"Latily, I expofed fome calx of lead to the heat of the lens in inflammable air, received immediately from the veffel in which it was generated from iron and oil of vitriol, because this contains lefs water than that which has been received in water and confined by it; and when 6 or 7 ounce meafures of the air were abforbed, 1 could not fuppofe, from the ap pearance, that the water could be more than a quarter of a grain. However, when I repeated the experiment once more, I thought there might be about half a grain of water, which is more than I can well account for, without fuppofing that the water which was neceffary to the conftitution of inflammable air, and which I fuppofe to be about half its weight, was left

behind when the pure phlogiston revived the calx. This, therefore, is the opinion to which I am in

clined; fo that I do not think that any water enters into the conflitution of any of the metals."

HE well known advantages that have accrued to experimental philofophy, and to the arts, particularly thofe that depend on chemical proceffes, from the ufe of portable furnaces, render it unneceffary to fay any thing in commendation of the invention; but as by them gentlemen of rank and fortune (from whom experiments are chiefly to be expected) are enabled further to profecute those fludies, which have already been the origin of many of the benefits the public reap from the prefent improved ftate of our manufactures, it may not be unprofitable to give a fhort account of the invention, defcribe the feveral kinds moft in ufe; and as all hitherto contrived have laboured under fome objections, to fhew a cheap and easy method, confirmed by confiderable experience, by which thofe defects are remedied, and the use of fuch furnaces rendered more agreeable and commodious.

"It is not in this paper intended to defcribe the feveral forms, which fometimes the judgment and fome times the caprice of the maker have adopted, but to fhew that the materials of which they have been constructed, though fit for the purpofe intended, have nevertheless been hardly ever properly applied; and then lay before the reader, the

method alluded to above, of obviating the objections hitherto made to them.

nus.

"To the celebrated John Joa. chim Becher we owe the inven tion of portable furnaces, contrived for performing the different kinds of chemical proceffes, of which he has given us a full hitlory and ex. planation, with many plates, in his work entitled, Scyphus Becheria❤ In the introduction to that work, the author fays, That having obferved fome workmen melt iron in a fimall furnace, it occurred to him that fomething might be contrived by which the feveral chemical proceffes might be conveniently performed; and that having completed his ideas on this head, fome of the first furnaces made were purchased by Dr. Dicken'on, phyfician to the king, prince Rupert, and the honourable Mr. Boyle.

"He directs the furnace to be made of plate-iron, having rivets faftened at different places, with heads projecting fufficiently within the infide of the furnace : As the furnace was to be (to the thickness of an inch and half) lined with a lute compofed of clay and fand; thefe rivets were intended to prevent its cracking, and falling from the fides.

"The use of fuch a contrivance as this appeared fo commodious to