I could fhut the orifice of the ftrong glafs velel in which the explotions were made, I had two perforations. Through one of thefe I poured the mercury, by means of a gl.fs funnel; but into the other was introduced a glafs tube, which, being bended, was in erted, by means of a cork, into a thin glafs vefiel, 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 mercu y, neceffarily pafs through the glafs tube, and be diffufed through the thin glafs veffel; in which I imagined that all its contents, fluid or folid, must 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, belides a fmall quantity of water; which, added to the water collected in the ftrong 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 coure 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 conteins much foot, is foon difperfed, and becomes invifible 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 vcffel 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.

Hoping to fucceed better in collecting this volatile matter by means of a quantity of water incumbent upon the mercury, in the ftrong glafs veffel in which the explofions were made (though I had found that part of it could escape through the water) I decompofed a great quantity of the two kinds of air in thefe circumflances; 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 mafs 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 myself whether it was a proper foot or not.

Mr. Warltire first observed this cloudiness in a veffel in which he burned inflammable air; but it is temarkable that fometimes I got it repeatedly in thefe explofions, 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 deter mine 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 blackness difappeared, leaving the infide of the vefiel covered with finall globules of white mercury it feems, there

fore,

fore, that part of the phlogifton of the inflammable air fometimes attaches itself to the vapour of mer cury, diffufed inviably 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 burn ing inflammable and dephlogitti cated air is evident from the experiments of Mr. Cavendish and Mr. Lavoifier. I have alfo frequently collected confiderable quannities of water in this way, though never quite fo much as the weight of the two kinds of air decompofed. 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 continua ly iffued inflammable air, from a veffel containing iron and oil of vitriol This being lighted, continued to burn like a candle. Presently after the lighting of it, the inude of the balloon 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 condented. 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 team, and capable of being conveyed a great way through air, or even water, without condenfation, 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 condenied by cold, is very little understood, but well deferves the particular attention of philofophers. Even mercury will evaporate, fo as to lose weight, in a degree of heat below that of boiling water.

"That the water collected in the balloon comes from the decompofition 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 fulphura ed iron, there was a denie white cloud that filled the infide of the balloon. There was also a strong smell 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 leaft as produced from iron, it still 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 ne ceffary 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 moif ture 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 existed extraneously 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 conflitutes inflammable air goes into a calx, in order to form the metal; fo that if this, though a compound thing, be called phlogifion, it will fill be true that phiogitton and inflammable air are the fame thing; but, on the whole, I rather think that the water which was effential to the constitution of inflammable air was left behind.

"That water, however, may exist in bodies in a combined ftate, without appearing to be water, we know in many cafes; but it is in nothing more evident than in the feales of iron, than which no fubflance 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 64 ounce measures of inflammable air from iron, I revived lead till it was reduced to 1 ounce measure, 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 fubftance. It ought alfo to be confidered that it must be exceedingly difficult to expel al moisture by mere heat from fuch a powdery fubftance as the yellow calx of lead, without reviving the

metal.

All chemis well know how firmly moiflure adheres to many fubitances, with which it does not properly unite, and how much heat is neceffary to separate 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 reafon to think might have been in the veffel, independently of what was contained in the inflammable air; and in order to enable my felf 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 glass, 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.

"Lastly, I exposed 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, I could not fuppofe, from the appearance, that the water could be more than a quarter of a gra`m. 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 te about half its weight, was left

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

"T"

HE well known advantages that have accrued to expe rimental philofophy, and to the arts, particularly thofe that de; end on chemical procefles, 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 thofe fludies, which have already been the origin of many of the benefits the public reap from the prefent improved state of our manufactures, it may not be unprofitable to give a fort account of the invention, defcribe the feveral kinds moft in ufe; and as all hitherto contrived have laboured under fome objections, to flew a cheap and eafy method, confirmed by confiderable experience, by which thofe defects are remedied, and the use of such furnaces rendered more agreeable and commodious.

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

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

"To the celebrated John Joachim Pecher we owe the invention of portable furnaces, contrived for performing the different kinds of chemical proceffes, of which he has given us a full hillory and explanation, with many plates, in his work entitled, Scyphus Becherianus. In the introduction to that work, the author fays, That having obferved fome workmen melt iron in a fmall furnace, it occurred to him that fome Ling might be contrived by which the feveral chemical procefles might be conveniently perfon ed; 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 Jute compofed of clay and fand; these rivets were intended to prevent its cracking, and falling from the fides.

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

the

the late Dr. Shaw, and Mr. Hawkfbee (to whom the prefent tafte for chemical experiments, is in a great degree owing), that in the year 1721 they published, with confiderable additions to Becher's tract, a fmall volume entitled, "An Effay for introducing a Portable Laboratory", for which, as they ingenuously acknowledge, they were almost wholly indebted to Becher. The furnace defcribed by Dr. Shaw and Mr. Hawkfbee differs little from that of Becher, and, like it, is intended to be lined with a lute, which is to be fecured to the iron plate by means of rivets.

"This has been hitherto almoft the univerfil practice in forming portable furnices for chemical experiments; and it is but juffice to fay, that to thefe authors are to be afcribed the invention and introduction of furnaces on this conftruction, however the fhapes may have been varied fince their time.

"Another kind of portable furnaces, if they may be faid to de ferve the title, were contrived by Johanne Francifco Vigani, and the defeription of them, with figures, published by him in a fmall treatife entitled, Medulla Chymiæ; printed in London 1683, and dedicated to three English noblemen.

"As thefe furnaces confifted folely in having a number of bricks, fo fitted together and marked, that they might eafily be taken afunder, when an operation was finifhed, and commodioutly fet afide until they fhould be again wanted, the frequent miflaying, or lofs of the loofe bricks, foon brought this kind of furnace into difufe, in experimental laboratories; though it must be owned, it has in many cafes fome advantages, and is often ufed, to this day, by plumbers, and other workmen.

"About the year 1750, the late Dr. Lewis, whofe name and memory will ever be refpected by al votaries to chemidry, obferving the inconveniencies that attended the ufe of both the foregoing kinds of furnaces, and taking the hint, as he candidly acknowledges, from an ingenious workman, and alto reflecting on the durability of black lead crucibles, and the eafe with which the openings for doors, chimneys, &c. are made in them, contrived thole portable furnaces, fo accurately, and fo properly defcribed by him, in the first part of his excellent work, entitled, The Philofophical Commerce of Arts; a work, which if he had met with due encouragement to profecute, and had completed according to his ideas on the fubject, would have done infinite honour to himself and to his country. Since that time, it does not appear that any one has made an effential alteration in the conftruction of these kinds of inftruments, except the ingenious Mefirs Ruhl and Hempel, of Cheyne Row, Chelfe, who having, under the patronage of the Society, eftablished a manufactory of black lead pots, and profiting by the thoughts of Dr. Lewis, have employed themfelves in making furnaces, in a very neat and commodious manner, of the fame materials their pots are formed of; and the only objection to them, is the price at which they muft neceffarily be fold, on account of the value of the materials, and the workmanfhip; in every other refpect, they antiver well the purposes they are in ended for, being ingeniously contrived, and executed in a workmanlike manner.

"It would be highly improper here to omit obferving that the juftly admired Boerhaave, mentions

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