"It is alfo by virtue of this fuperior attraction to the fiery matter, that ice, refin, fats, and other vapourable bodies, become fluid by moderate incalefcence, but not before they have received a great quantity of fire; and that they refpectively evaporate with lefs ignition or incalefcence, in veffels which avert the preffure of the aerial atmofphere, than where that, or any equivalent compreflion, confpires with their aggregate attractions, to refift the influx of fire, and the difjunction of their parts.-Thus water, or fpirit, moderately heated, and placed in the receiver of an air-pump, boils when a part of the air which compreffes it is drawn out, and ceases as often as the preffure is restored. "Still fronger attractions of the matter of fire, comparatively with the forces which tend to the exclufion of it, are feen in ethereal oils and ethers for their vapours can not be condenfed without the aid of compreffion; and when they are thus condenfed and aggregated, their molecules, by attracting fiery matter and compelling it into atmofpheres, with forces fuperior to thofe with which they attract each other, are made to recede, and form aeriform fluids, in the lowest temperatures, fo foon as the preffure of the atmosphere is averted. "That the expanfion of fuch ethereal fluids into the aerial form, in the exhausted receiver of an air-pump, is owing to the tendency of their molecules, to attract the matter of fire and to form at mofpheres of it around them feverally, and that it is not effected by any other agency, is apparent from the concomitant phenomenon of cold for as faft as they affume the aerial form, they engage and fix the free fiery matter which belong. ed to the spaces into which they expand; and this privation or deficiency of difengaged fiery matter, is what we call cold. "The bodies which by ignition may be partially or totally converted, even under the atmosphe ric preffure, into fluids permanently elastic, fhew the kinds of matter by whi h that of fire is attracted in the fupreme degree. "For the elasticity which fubfifts under immenfe preffure, argues a ftronger attraction of the particles to their refpective repellent atmospheres, than that which we laft notice; but that this stronger attraction compels denfer and deeper atmospheres, may not only be argued a priori, but is experimen tally demonftrable by the bulk, which in elastic fluids is the mea. fure of the atmospheres, compared with the gravity, which is the measure of the grofs particles; and it is alfo apparent in the extraor dinary quantity of the fiery matter that efcapes in the inftant of the aggregation of thefe elastic fluids, or rather of their particles, to form confiftent bodies; as when empyreal air is rapidly imbibed by phofphorus, pyrophorus, hepar fub phuris, or iron filings and fulphur; when alkaline air, and divers acid airs, are abforbed by water, or when they condenfe each other; or when the rare inflammable air and empyreal air make water, and exclude their matter of fire. "From all this it may be inferred, that in any future table of the affinities of the matter of fire, pure phlogifton ought to rank above every other kind of matter; intead of being omitted, as it is in Berge man's tables, or fuppofed to have repugnance or apathy to the mat ter of fire, as Dr. Crawford formerly conjectured. But when this precedence 1 precedence is given to phlogiston, by reafon of the extreme levity of the purer inflammable air of metallic folutions, and of the quantity of fiery matter which it emits in the inftant of its union with empyreal air, the gravitating matter of this laft air must not be placed beneath any other that is now known; because no air that is free from phlogiston, is lighter fpecifically than empyreal air, or emits more fire in the inftant of aggregation. "I confider the fpecific gravity as a fafe guide in our investigations of thefe affinities and of their order, in regard only to the elastic fluids which feem to confift of no more than one kind of gravitating matter engaged in the repellent atmospheres and of fixable air, denfe inflammable air, acid airs, the phlogistic alkaline air, and others, I would obferve, that the atmofpheres include molecules inftead of folitary ultimate parts; for without this chemical union of heterogeneal parts, and the formation of molecules, an elastic fluid of the kind that I now speak of, could not differ, as it does, from either kind of matter of which it is compofed. "From this confideration of the attractive forces which tend to form molecules, and of the atmofpheres, which, in compound elattic fluids, encompass the molecules, but not the ultimate parts feverally, we derive an eafy explanation of the phenomenon fo often noticed in the preceding pages; I mean the convertion of a fubftance, not into one but into two or three different elaftic fluids, by mere ignition. "When elastic fluids are formed in folutions and other procefles, in which the fubjects are not ig nited it is to be observed that the gravitating parts of the emitted claftic fluid, were distant from each other, by reafon of the interfpofed matter, at the inftant of their ex-, trication, and that at this diftance there is a great diminution of the powers which restrain them in their tendency to engage all the matter of fire that the menftruum or folvent could extricate during their union. Thus it happens, as Dr. Black originally fuggefted, and as Bergman has obferved in his excellent Differtation of Elective Attractions, that cauftic alkali, in the union with an acid, excites great heat, that is to fay, in their union they exclude a part of the matter of fire which they feverally held in a fixed ftate; but mild alkali, in uniting with an acid, gives little or no heat, and for this reafon; that the gravitating parts of the fixable air, engage all the liberated matter of fire in forming atmospheres around its molecules. This expofition is applicable to every other elaftic fluid that is extricated in folutions or combinations attended with little or no incalefcence. "Since the particles which attract the matter of fire, exc.ude a part of their refpective charges in the inftant of their clofe approximation or contact, there is no dif ficulty in accounting for the cold produced in folutions, expanfions, and evaporations; in every one of which, the particles which refume the matter of fire, and in fixing it produce the cold, are previously removed to fome diflance from each other, either by the interpofition of the parts of a menftruum, as when ice is diffolved by nitrous acid, or by the prevalent powers of their proper fixed fire, of which we have an inftance in ether placed in the exhausted receiver of an airpump. "As the mere acetous acid confifts of the gravitating parts of empyreal air, of phlogifton, and the acid principle of vegetables, and by the acceffion of the matter of fire only makes two different elastic fluids, namely fixable air, and denfe inflammable air, it follows from thefe notions, that the gravitating parts of these two airs would make acetous acid again with water, if the matter of fire could be withdrawn from them; and I venture to prognofticate that this, or fomething equivalent, will be done by the firft ingenious experimenter that attempts it, either by the means of a body which may absorb the gravitating matter of both, and exclude their atmospheres, or by breaking the atmospheres, in the manner which I am to describe in the next fection. "There is undoubtedly a natural limitation, as we formerly obferved, of the forces with which the grofs parts of divers elattic fluids compel, and are compelled by their refpective atmospheres; but ftill thefe forces are fo great, that we cannot form adequate ideas of them, without reflecting on the refiftance which they give, even in fmall quantities of the elaftic fluids, to any preffure which tends to condenfe them, and caufe an approximation of their parts; or without adverting to the operations which fhew the ability of thefe forces to maintain the elaficity of divers aeriform fluids, in oppofition to the greatest mechanical powers hitherto employed to fubdue them. The air-gun, and other inftruments exhibit thefe forces in atmofpheric air, and chemical operations and explofive compofitions too often fhew them in the other elaftic fluids. "Although the force of chemical attraction reaches not far from the particles, with any fentible effect, we are not thence to conclude that the attractive virtue ceases at any distance. But from all the known phenomena we may infer, that the attractive forces, tending to the approximation and cohefion of grofs particles, decrease in a duplicate, or fome higher ratio of the diftances, reciprocally that the natural refiftance to the interpofition of the fiery matter, is leffened at the fmalleft, and totally overpowered at fmall distances which no eye can measure; and finally, that where the fenfible effect of attraction ceafes, there repulfion fucceeds." OBSERVATIONS on the COMPOSITION of WATER. [From the Third Volume of Dr. PRIESTLEY'S EXPERIMENTS and OBSERVATIONS relating to various Branches of NATURAL PHILOSOPHY.] T "HAT dephlogifticated and inflammable air, at least with the element of heat, constitute water, feems to be clearly inferred from the experiments in the preceding fection. Some difficulties, however, have occurred respecting this theory, from my fubfequent experiments, T experiments, which I fhall propofe with the fame fidelity as I have done thofe which favour the hypothefis. But as I mean to throw into this fection all the obfervations that I have made upon the fubject, I fhall first recite fome experiments which perfectly agree with the former, and evidently lead to the fame conclufion. Some of them are those of which only the general refult was given before. "I have obferved, that, when that iron which has been melted in the open air (or that which has been altered by the paffing of fteam over it red-hot) was heated by a burning lens in inflammable air, the air difappeared, and a confiderable quantity of water was pro duced. I had the fame refult with feales of copper. Thefe fcales became of a genuine copper colour in this procefs; fo that I had no doubt of their being copper revived. The water was fo copious, that when only 3 ounce measures of air were abforbed, the water formed in drops on the infide of the veffel, and fome of them ran down it. เ "I alfo procured water when I decompoted dephlogisticated and inflammable air from iron by the electric fpark in a clofe veffel, which is an experiment fimilar to thofe that were made by Mr. Lavoifier, at Paris. I put 3,75 ounce meafures of a mixture of air, of which one-third was dephlogifticated, and two-thirds inflammable from iron, in the clofe veffel; and after the explosion 1 found in it one grain of moisture. The dephlogisticated air in this mixture would have weighed a little more than 0,75 of a grain. But repeating this experiment with half as much dephlogificated as inflammable air, I could not perceive any water after the experiment. Neither was there any fixed air formed in it. Again, ufing inflammable air from wood, in the fame proportion from 3,8 ounce meafures of the mixture, I got 0,8 of a measure of fixed air, which was actually obforbed by lime-water. Some water alfo was evidently produced. "Uling more precautions to exclude all water from either of thefe two kinds of air before the experiment (both the dephlogisticated air, which was from nitre, and the inflammable air which was from charcoal, being from the first received in mercury, and always confined by it) I still found a little water after the explosion. "I varied this experiment by producing the inflammable air in the dephlogisticated air as follows. Into a veffel containing dephlogifticated air confined by mercury, I introduced a piece of perfect charcoal, as hot from the fire as I could bear to handle it, and threw upon it the focus of the lens, fö that a quantity of the air was imbibed; but I could not perceive that any moisture was formed. Afterwards, when I refumed the procefs, the air which the charcoal had imbibed was expelled again, and very little more was abforbed. From feven ounce measures there remained four, of which more than two was pure fixed air. No water could be expected after this process. For even had there been a small quantity of moisture in the veffel, it would have been abforbed by the charcoal, and have enabled it to yield inflammable air. The phlogiston the charcoal contained uniting with the dephlogisticated air, free from moisture, formed, I prefume, the fixed air that was found after this procefs. "But the greatest difficulty that H 3 occurred, occurred with respect to the preceding theory of the conftitution of water, arofe from my never having been able to procure any water when I revived mercury from red precipitate in inflammable air, or at least not more than may be fuppofed to have been conta ned in the inflammable air as an extraneous fubitance. "In order to make the experiments with the fales of iron, and that with the red precipitate as much alike as poffible, and that I might compare them to the greatest advantage, I made them immediately one after the other, with every circumftance as nearly as I could the fame. The inflammable air was the fame in both the experiments, and both the fcales of iron, and the red precipitate, were made as dry as poffible. They were heated in veffels of the fame fize and form, and equally confined by dry mercury. And yet when I heated the former, water was formed as copioufly as I have defcribed it before, viz, actually running down the infide of the veffel in drops, though only four ounce measures of inflammable air were abforbed. But though I heated the red precipitate till eight ounce meafures of the inflammable air was abforbed, and only threefourths of an ounce meafure of air remained, there was hardly any fenfible quantity of water produced, certainly not one-tenth of what appeared in the experiment with the fcales of iron. "There was this difference, however, in the two refults. In what remained from the experiment with red precipitate, I at this time perceived a flight appearance of fixed air, whereas there was none in what remained from the fcales of iron. The refiduum alfo from the red precipitate had in it a very fmall portion of dephlogisticated air. For being mixed with an equal measure of nitrous air, the standard. of it was 1,8. I must also obferve that the inflammable air difappeated much more rapidly in the procefs with red precipitate than in that with the fcales of iron. "Fixed air, however, was no neceffary refult in this experiment. For I particularly obferved, that when, upon another occafion, I reduced eight ounce measures of inflammable air to 0,22 of a meafure, I found no more than what I judged to be much less than a grain of water, and without any appear ance of fixed air whatever. Again, 1 reduced fix ounce measures of inflammable air in this process to 0,12 of a measure, without producing any more water than before, or any fixed air at all. I alfo had the fame refult in ufing the black powder of lead and mercury, initead of red precipitate: reducing 6,5 ounce measures to 0,4 of a meafure, without finding any very fentible quantity of water, or any fixed air. In this experiment there can be no doubt but that the dephlo gifticated air diflodged from the red precipitate, united with the inflammable air in the veffel; as no water equal to the weight of the two kinds of air was produced, they must have formed fome more folid fubftance, which, in the fmall quantities I was obliged to use, could not be found. "It may be clearly inferred from this experiment, that red precipitate is a fubftance by no means fimilar to the fcales of iron, as the latter appears to contain within itself all the elements of water; and, therefore, as the inflammable air enters into it, a quan |