Chemical Observations and Experiments on Air and Fire

"Researches on Air... may furnish sufficient materials for new discoveries to every one who chuses to set about making Experiments."

"Fire, that is so wonderful, cannot be generated without Air."

"I presume in this Treatise.. to alledge proofs, that a kind of Air subsisting in our atmosphere is a true constituent part of Fire, and materially contributes to the existence and support of flame; for which reason I call this Air empyreal Air (Fire Air [oxygen])."

"He [ Joseph Priestley ] still adhered to the old opinion that all pure alkalies and absorbent earths must effervesce with acids."

"I take it as a certainty for granted, that pure water in itself can neither by art nor nature be changed into a dry substance, which shall have all the properties of a true earth. ...the white earth was nothing else than the most subtle powder of glass."

"The object and chief business of Chemistry consists in a skilful decomposition of bodies into their integrant parts, and in combining them again in various manners. Only those can be ignorant how difficult it is to execute this business with the greatest accuracy, who either never undertook it or never bestowed upon it the required degree of attention."

"Hitherto chemists are not agreed upon the number of simple principles or elements, of which all corporeal substances are composed. ...Others believe that earth and phlogiston are those principles which are the constituent parts of all corporeal substances. The greatest number seem to admit only the peripatetic elements."

"I found the great necessity to know the Fire, since it is impossible to make experiments without heat and fire, or to produce any effects with any solvent; I began to set aside all the definitions of Fire; I made numerous experiments, in order to investigate, if possible, this glorious subject. I soon found, that without knowing the Air, it is impossible to form a true judgment on the phænomena of Fire."

"After a series of experiments, I observed, that Air really makes part of the compound of Fire, and is a constituent part of the fame and of sparks. I concluded, therefore, that a Treatise on Fire, could not be drawn up with any degree of accuracy, without an enquiry into Air."

"Air is... mixed with another elastic fluid similar to air, and which is in many respects differing from it, called very properly by Professor Bergman, Aërïous Acid. It owes its existence to the destruction of organic bodies by putrefaction or combustion. Nothing has of late so much engaged the attention of natural philosophers, as this subtle acid, or fixed air. It is no wonder, since inferences drawn from the properties of this elastic acid, are by no means favourable to all those who are possessed by prejudice."

"The partisans of the Paracelsian doctrine are of opinion, that air is properly not subject to alteration or change: others think with Hales, that it may be mixed with other bodies; but that it then loses its elasticity; which it again recovers, as soon as it is disengaged either by fire or fermentation. But observing, that this disengaged air is possessed of properties widely different of those in common air; they conclude (without being founded on experience) that this Air is charged with heterogeneous particles; and that the Air ought to be cleared of the heterogeneous matter by shaking and filtrating it with various fluids."

"I believe this opinion might be adopted without the least hesitation, if it only could be clearly proved by experiment, that a certain quantity of common Air may be changed, by the mixture of adventitious substances, into fixed or other Air: but as this has not as yet been put into execution, I suppose myself right, by adopting as many kinds of Air, as are extricated by experience."

"Having collected an elastic fluid, and observing that its elasticity is increased by heat and diminished by cold; when at the same time it retains constantly its elastic fluidity, and has properties and relations quite different of those, which are found in common Air I think myself entitled to conclude that this is a peculiar kind of Air, I assert that such collected Air ought to preserve its elasticity even in the most intense cold; since otherwise innumerable kinds of Air must be allowed; as it is highly probable that all substances may be changed into a vapour similar to Air by an intense heat."

"Substances undergoing either putrefaction or decomposition by Fire, diminish or as it were absorb part of the Air. Sometimes it happens that they considerably increase the bulk of the Air, and in other instances, these substances will neither increase nor diminish a certain given quantity of Air; all which are very remarkable phænomena."

"Surmises cannot determine any thing with certainty, and they will still less satisfy a chemical natural philosopher, who always wants demonstrative proofs. This clearly shews the necessity of making experiments, in order to elucidate this mystery of nature."

"1. Fire burns for a certain time in a given quantity of Air. 2. If the Fire does not yield during combustion a fluid similar to air, after the spontaneous extinction of the Fire, air is diminished between a third and a fourth of its bulk. 3. It is not miscible with common water. 4. All kind of animals live but a certain time in a given quantity of confined air. 5. Seeds, as for instance peas, will strike roots and grow to a certain height in a given quantity of equally confined air, by the addition of some water and moderate heat."

"Hence if a fluid be exhibited similar in all external appearances to Air, but which upon examination wants the enumerated qualities, (should even only one be wanting,) I should think myself convinced, that it is not common air."

"It appears from all these Experiments, that in each of them phlogiston, the simple inflammable principle, is present. It is well known, that Air attracts the inflammable part of bodies, and deprives them of it: not only this may be seen from the above Experiments, but it also appears that in the transition of what is inflammable principle into the Air, a considerable part of the Air is lost; but that what is inflammable principle is the sole cause of this effect, is evident..."

"It likewise appears that a given quantity of Air can be united to or saturated as it were only by a certain quantity of phlogiston..."

"Air is composed of two different fluids, the one of which attracts not the phlogiston, and the other has the quality of attracting it, and this latter fluid makes between a third and a fourth of the whole bulk of the air."

"These experiments seem to prove, that the transition of phlogiston into the air diminishes not always its bulk; which however other experiments clearly indicate..."

"What we now are going to mention, demonstrates that the part of air, which unites with the inflammable, and is in a manner absorbed, is again restored by the re-extricated aerial acid (fixed air)."

"Certainly it is a remarkable circumstance to observe, that the phlogiston separated from bodies, either without or with a fiery motion, and united with air, always considerably diminishes the bulk of air."

"It might be objected that the lost air is still contained in the residuum of air which could not farther be united with the phlogiston; for finding that kind of air lighter than common air, it might be supposed that the phlogiston when united with this air made it less ponderous, which circumstance is already known from other experiments. However, since phlogiston is a substance, (which always supposes some weight,) I very much doubt whether this hypothesis be founded on truth."

"I will prove, that by the union of air with the inflammable principle, a compound is formed, so subtle as to pass through the fine pores of the glass, and disperse all over the air."

"I took a glass retort, capable of containing eight ounces of water, and distilled fuming spirit of nitre according to the usual method. In the beginning the acid passed over red, then it became colourless, and lastly again all red: no sooner did this happen, than I took away the receiver; and tied to the mouth of the retort a bladder emptied of air, which I had moistened in its inside with milk of lime lac calcis, (i.e., lime water, containing more quicklime than water can dissolve)... to prevent its being corroded by the acid. Then I continued the distillation, and the bladder gradually expanded. Hereupon I left every thing to cool, tied up the bladder and took it off from the mouth of the retort.—I filled a ten ounce glass with this air... and put a small burning candle into it; when immediately the candle burnt with a large flame, of so vivid a light that it dazzled the eyes. I mixed one part of this air with three parts of air, wherein fire would not burn; and this mixture afforded air, in every respect similar to the common sort. Since this air is absolutely necessary for the generation of fire, and makes about one third of our common air, I shall henceforth, for shortness sake call it empyreal air, [literally fire-air:] the air which is unserviceable for the fiery phenomenon, and which makes about two-thirds of common air, I shall for the future call foul air [literally corrupted air]."

"My apparatus and vessels are the most simple that can possibly be found. Matrasses, retorts, bottles, phials, and ox-bladders are the things which I employ."

"If I want to collect a certain kind of air, for instance, phlogisticated acid of nitre... I take a soft bladder, rubbed on its inside with a few drops of oil, I put into it the filings of some metal, iron, zinc, or tin. I then carefully expel, by compression, all the air contained in it, and tye the bladder to the mouth of a small phial, into which I had poured some aquafortis; I unfold the bladder a little, that some of the steel filings may fall into the aquafortis; and in proportion as they are dissolved the bladder is expanded. When I have a sufficiency of such air, I tye the orifice of the bladder pretty close with a string, and take it off from the phial."

"These are the methods employed by me in my enquiries on air. I confess that they will not please every body, since they decide not to a nicety: but in my enquiries they have all proved satisfactory: and often people pretend to split even a hair, where there is no necessity to attend to minutiæ."

"Had the Chemists of last century vouchsafed to examine more minutely the elastic fluids similar to air, which appear in so many operations, we should at present be farther advanced. They wanted to see every thing in corporeal form, and collect them as drops in the receiver. It has been better enquired into in our days; and air has been examined; and who is not sensible of the utility of the results of such experiments?"

"I have declared that saltpetre alone will decompound the substance of heat.—The following experiment proves it. I put one ounce of saltpetre purified for distilling, into a glass retort, and employed a moistened bladder, emptied of air, in lieu of a receiver. (fig. 3.) As soon as the saltpetre became red hot, it began boiling; and at that period of time the bladder was expanded from the air that passed over. I continued the distillation till the boiling in the retort ceased; and the saltpetre was on the point of penetrating through the softened glass retort. In the bladder I found the pure empyreal air, taking up the space of fifty ounces measure, This is the best and cheapest method of obtaining empyreal air."

"Scheele realized that common air contained a component that was responsible for combustion and termed this component fire air. Scheele succeeded in isolating fire air by reacting nitic acid (HNO3) and potassium hydroxide (KOH) to obtain potassium nitrate (KNO3) and then heated the potassium nitrate and used a salt to absorb the nitrogen oxides from the gas produced. The process resulted in fire air."

"In 1774, Scheele obtained a yellow gas by digesting marine acid with manganese (manganese dioxide). As Scheele supposed that the manganese withdrew phlogiston from the acid, he called the new gas dephlogisticated marine acid. When, at a later time, phlogiston was regarded by some chemists as identical with hydrogen, Scheele's view of the relation between the compositions of marine acid and the gas he obtained by the reaction of that acid with manganese oxide was interpreted to mean that the gas was produced by removing hydrogen from the acid. In accordance with his conception of the composition of acids, Lavoisier regarded muriatic acid to be a compound of oxygen; and in order to trace a likeness between the supposed composition of this acid and the compositions of other acids, he asserted that muriatic acid is formed by the union of oxygen with a hypothetical substance which he named radical muriatique. Lavoisier described the reaction between muriatic acid and manganese oxide as an oxidation of the acid; he said that the addition of a second dose of oxygen made the acid more volatile, but less acidic. He named Scheele's yellow gas acide muriatique oxygéné."

"He employed the simplest kinds of apparatus; and since his work dealt with the isolation of new substances and the examination of their properties, he was not concerned, like his contemporary, Black, with the use of a balance in following his observations. So early in 1770 Scheele had found how to produce 'inflammable air' (hydrogen) by treating iron or zinc with an organic acid and water. ...By 1773 he had isolated oxygen by heating silver carbonate, mercuric oxide, saltpetre, and other substances... Scheele showed that this new gas, which he called Feuerluft ('fire-air'), was identical with the 'lost air' which was absorbed by ordinary air by damp iron filings or by phosphorus; also that ordinary air consists of a mixture of about one part of 'fire air' with four parts of 'spent air.'"

"Finding air necessary for the of fire, Scheele first turned his attention to its analysis; he found that solution of liver of sulphur, and certain other sulphureous compounds, occasioned a diminution in the bulk of air, to which they were exposed, equal to one part in about five, the flame of hydrogen and that sulphur caused a similar decrease of bulk in air standing over water, and lime-water not being rendered in either case turbid by the residuums, no fixed air was formed. He then obtains empyreal air (oxygen) by the decomposition nitric acid, and other processes; describes the method of transferring, collecting, and examining the gases, and endeavours to prove that heat is a compound of empyreal air and phlogiston; he also shows by direct experiments, that the absorption occasioned in atmospheric air by liver of sulphur, is referrible to the abstraction of its empyreal portion; that it totally absorbs empyreal air, and that, upon adding to the residuary portion of atmospheric air, a quantity of empyreal air, equal to that absorbed by the sulphureous liquor, an air is again compounded, similar in all respects to that of the atmosphere. The identity of these investigations with those of Priestley will not fail of being observed, but... although Priestley was in the field a little before him, Scheele was unacquainted with his proceedings."