SECTION VIII.

Of the effect of the CALCINATION of METALS, and of the EFFLUVIA of PAINT made with WHITE-LEAD and OIL, on AIR.

Having been led to suspect, from the experiments which I had made with charcoal, that the diminution of air in that case, and perhaps in other cases also, was, in some way or other the consequence of its having more than its usual quantity of phlogiston, it occurred to me, that the calcination of metals, which are generally supposed to consist of nothing but a metallic earth united to phlogiston, would tend to ascertain the fact, and be a kind of experimentum crucis in the case.

Accordingly, I suspended pieces of lead and tin in given quantities of air, in the same manner as I had before treated the charcoal; and throwing the focus of a burning mirror or lens upon them, so as to make them fume copiously. I presently perceived a diminution of the air. In the first trial that I made, I reduced four ounce measures of air to three, which is the greatest diminution of common air that I had ever observed before, and which I account for, by supposing that, in other cases, there was not only a cause of diminution, but causes of addition also, either of fixed or inflammable air, or some other permanently elastic matter, but that the effect of the calcination of metals being simply the escape of phlogiston, the cause of diminution was alone and uncontrouled.

The air, which I had thus diminished by calcination of lead, I transferred into another clean phial, but found that the calcination of more lead in it (or at least the attempt to make a farther calcination) had no farther effect upon it. This air also, like that which had been infected with the fumes of charcoal, was in the highest degree noxious, made no effervescence with nitrous air, was no farther diminished by the mixture of iron filings and brimstone, and was not only rendered innoxious, but also recovered, in a great measure, the other properties of common air, by washing in water.

It might be suspected that the noxious quality of air in which lead was calcined, might be owing to some fumes peculiar to that metal; but I found no sensible difference between the properties of this air, and that in which tin was calcined.

The water over which metals are calcined acquires a yellowish tinge, and an exceedingly pungent smell and taste, pretty much (as near as I can recollect, for I did not compare them together) like that over which brimstone has been frequently burned. Also a thin and whitish pellicle covered both the surface of the water, and likewise the sides of the phial in which the calcination was made; insomuch that, without frequently agitating the water, it grew so opaque by this constantly accumulating incrustation, that the sun-beams could not be transmitted through it in a quantity sufficient to produce the calcination.

I imagined, however, that, even when this air was transferred into a clean phial, the metals were not so easily melted or calcined as they were in fresh air; for the air being once fully saturated with phlogiston, may not so readily admit any more, though it be only to transmit it to the water. I also suspected that metals were not easily melted or calcined in inflammable, fixed, or nitrous air, or any kind of diminished air.[8] None of these kinds of air suffered any change by this operation; nor was there any precipitation of lime, when charcoal was heated in any of these kinds of air standing in lime-water. This furnishes another, and I think a pretty decisive proof, that, in the precipitation of lime by charcoal, the fixed air does not come from the charcoal, but from the common air. Otherwise it is hard to assign a reason, why the same degree of heat (or at least a much greater) should not expel the fixed air from this substance, though surrounded by these different kinds of air, and why the fixed air might not be transmitted through them to the lime-water.

Query. May not water impregnated with phlogiston from calcined metals, or by any other method, be of some use in medicine? The effect of this impregnation is exceedingly remarkable; but the principle with which it is impregnated is volatile, and intirely escapes in a day or two, if the surface of the water be exposed to the common atmosphere.

It should seem that phlogiston is retained more obstinately by charcoal than it is by lead or tin; for when any given quantity of air is fully saturated with phlogiston from charcoal, no heat that I have yet applied has been able to produce any more effect upon it; whereas, in the same circumstances, lead and tin may still be calcined, at least be made to emit a copious fume, in which some part of the phlogiston may be set loose. The air indeed, can take no more; but the water receives it, and the sides of the phial also receive an addition of incrustation. This is a white powdery substance, and well deserves to be examined. I shall endeavour to do it at my leisure.

Lime-water never became turbid by the calcination of metals over it, the calx immediately seizing the precipitated fixed air, in preference to the lime in the water; but the colour, smell, and taste of the water was always changed and the surface of it became covered with a yellow pellicle, as before.

When this process was made in quicksilver, the air was diminished only one fifth; and upon water being admitted to it, no more was absorbed; which is an effect similar to that of a mixture of nitrous and common air, which was mentioned before.

The preceding experiments on the calcination of metals suggested to me a method of explaining the cause of the mischief which is known to arise from fresh paint, made with white-lead (which I suppose is an imperfect calx of lead) and oil.

To verify my hypothesis, I first put a small pot full of this kind of paint, and afterwards (which answered much better, by exposing a greater surface of the paint) I daubed several pieces of paper with it, and put them under a receiver, and observed, that in about twenty-four hours, the air was diminished between one fifth and one fourth, for I did not measure it very exactly. This air also was, as I expected to find, in the highest degree noxious; it did not effervesce with nitrous air, it was no farther diminished by a mixture of iron filings and brimstone, and was made wholesome by agitation in water deprived of all air.

I think it appears pretty evident, from the preceding experiments on the calcination of metals that air is, some way or other, diminished in consequence of being highly charged with phlogiston; and that agitation in water restores it, by imbibing a great part of the phlogistic matter.

That water has a considerable affinity with phlogiston, is evident from the strong impregnation which it receives from it. May not plants also restore air diminished by putrefaction by absorbing part of the phlogiston with which it is loaded? The greater part of a dry plant, as well as of a dry animal substance, consists of inflammable air, or something that is capable of being converted into inflammable air; and it seems to be as probable that this phlogistic matter may have been imbibed by the roots and leaves of plants, and afterwards incorporated into their substance, as that it is altogether produced by the power of vegetation. May not this phlogistic matter be even the most essential part of the food and support of both vegetable and animal bodies?

In the experiments with metals, the diminution of air seems to be the consequence of nothing but a saturation with phlogiston; and in all the other cases of the diminution of air, I do not see but that it may be effected by the same means. When a vegetable or animal substance is dissolved by putrefaction, the escape of the phlogistic matter (which, together with all its other constituent parts, is then let loose from it) may be the circumstance that produces the diminution of the air in which it putrefies. It is highly improbable that what remains after an animal body has been thoroughly dissolved by putrefaction, should yield so great a quantity of inflammable air, as the dried animal substance would have done. Of this I have not made an actual trial, though I have often thought of doing it, and still intend to do it; but I think there can be no doubt of the result.

Again, iron, by its fermentation with brimstone and water, is evidently reduced to a calx, so that phlogiston must have escaped from it. Phlogiston also must evidently be set loose by the ignition of charcoal, and is not improbably the matter which flies off from paint, composed of white-lead and oil. Lastly, since spirit of nitre is known to have a very remarkable affinity with phlogiston, it is far from being improbable that nitrous air may also produce the same effect by the same means.

To this hypothesis it may be objected, that, if diminished air be air saturated with phlogiston, it ought to be inflammable. But this by no means follows; since its inflammability may depend upon some particular mode of combination, or degree of affinity, with which we are not acquainted. Besides, inflammable air seems to consist of some other principle, or to have some other constituent part, besides phlogiston and common air, as is probable from that remarkable deposit, which, as I have observed, is made by inflammable air, both from iron and zinc.

It is not improbable, however, but that a greater degree of heat may inflame that air which extinguishes a common candle, if it could be conveniently applied. Air that is inflammable, I observe, extinguishes red-hot wood; and indeed inflammable substances can only be those which, in a certain degree of heat, have a less affinity with the phlogiston they contain, than the air, or some other contiguous substance, has with it; so that the phlogiston only quits one substance, with which it was before combined, and enters another, with which it may be combined in a very different manner. This substance, however, whether it be air or any thing else, being now fully saturated with phlogiston, and not being able to take any more, in the same circumstances, must necessarily extinguish fire, and put a stop to the ignition of all other bodies, that is, to the farther escape of phlogiston from them.

That plants restore noxious air, by imbibing the phlogiston with which it is loaded, is very agreeable to the conjectures of Dr. Franklin, made many years ago, and expressed in the following extract from the last edition of his Letters, p. 346.

"I have been inclined to think that the fluid fire, as well as the fluid air, is attracted by plants in their growth, and becomes consolidated with the other materials of which they are formed, and makes a great part of their substance; that, when they come to be digested, and to suffer in the vessels a kind of fermentation, part of the fire, as well as part of the air, recovers its fluid active state again, and diffuses itself in the body, digesting and separating it; that the fire so re-produced, by digestion and separation, continually leaving the body, its place is supplied by fresh quantities, arising from the continual separation; that whatever quickens the motion of the fluids in an animal, quickens the separation, and re-produces more of the fire, as exercise; that all the fire emitted by wood, and other combustibles, when burning, existed in them before in a solid state, being only discovered when separating; that some fossils, as sulphur, sea-coal, &c. contain a great deal of solid fire; and that, in short, what escapes and is dissipated in the burning of bodies, besides water and earth, is generally the air and fire, that before made parts of the solid."

FOOTNOTES:

[8] I conclude from the experiments of M. Lavoisier, which were made with a much better burning lens than I had an opportunity of making use of, that there was no real calcination of the metals, though they were made to fume in inflammable or nitrous air; because he was not able to produce more than a slight degree of calcination in any given quantity of common air.



SECTION IX.

Of MARINE ACID AIR.

Being very much struck with the result of an experiment of the Hon. Mr. Cavendish, related Phil. Trans. Vol. LVI. p. 157, by which, though, he says, he was not able to get any inflammable air from copper, by means of spirit of salt, he got a much more remarkable kind of air, viz. one that lost its elasticity by coming into contact with water, I was exceedingly desirous of making myself acquainted with it. On this account, I began with making the experiment in quicksilver, which I never failed to do in any case in which I suspected that air might either be absorbed by water, or be in any other manner affected by it; and by this means I presently got a much more distinct idea of the nature and effects of this curious solution.

Having put some copper filings into a small phial, with a quantity of spirit of salt; and making the air (which was generated in great plenty, on the application of heat) ascend into a tall glass vessel full of quicksilver, and standing in quicksilver, the whole produce continued a considerable time without any change of dimensions. I then introduced a small quantity of water to it; when about three fourths of it (the whole being about four ounce measures) presently, but gradually, disappeared, the quicksilver rising in the vessel. I then introduced a considerable quantity of water; but there was no farther diminution of the air, and the remainder I found to be inflammable.

Having frequently continued this process a long time after the admission of the water, I was much amused with observing the large bubbles of the newly generated air, which came through the quicksilver, the sudden diminution of them when they came to the water, and the very small bubbles which went through the water. They made, however, a continual, though slow, increase of inflammable air.

Fixed air, being admitted to the whole produce of this air from copper, had no sensible effect upon it. Upon the admission of water, a great part of the mixture presently disappeared; another part, which I suppose to have been the fixed air, was absorbed slowly; and in this particular case the very small permanent residuum did not take fire; but it is very possible that it might have done so, if the quantity had been greater.

The solution of lead in the marine acid is attended with the very same phaenomena as the solution of copper in the same acid; about three fourths of the generated air disappearing on the admission of water; and the remainder being inflammable.

The solutions of iron, tin, and zinc, in the marine acid, were all attended with the same phaenomena as the solutions of copper and lead, but in a less degree; for in iron one eighth, in tin one sixth, and in zinc one tenth of the generated air disappeared on the admission of water. The remainder of the air from iron, in this case, burned with a green, or very light blue flame.

I had always thought it something extraordinary that a species of air should lose its elasticity by the mere contact of any thing, and from the first suspected that it must have been imbibed by the water that was admitted to it; but so very great a quantity of this air disappeared upon the admission of a very small quantity of water, that at first I could not help concluding that appearances favoured the former hypothesis. I found, however, that when I admitted a much smaller quantity of water, confined in a narrow glass tube, a part only of the air disappeared, and that very slowly, and that more of it vanished upon the admission of more water. This observation put it beyond a doubt, that this air was properly imbibed by the water, which, being once fully saturated with it, was not capable of receiving any more.

The water thus impregnated tasted very acid, even when it was much diluted with other water, through which the tube containing it was drawn. It even dissolved iron very fast, and generated inflammable air. This last observation, together with another which immediately follows, led me to the discovery of the true nature of this remarkable kind of air.

Happening, at one time, to use a good deal of copper and a small quantity of spirit of salt, in the generation of this kind of air, I was surprized to find that air was produced long after, I could not but think that the acid must have been saturated with the metal; and I also found that the proportion of inflammable air to that which was absorbed by the water continually diminished, till, instead of being one fourth of the whole, as I had first observed, it was not so much as one twentieth. Upon this, I concluded that this subtle air did not arise from the copper, but from the spirit of salt; and presently making the experiment with the acid only, without any copper, or metal of any kind, this air was immediately produced in as great plenty as before; so that this remarkable kind of air is, in fact, nothing more than the vapour, or fumes of spirit of salt, which appear to be of such a nature, that they are not liable to be condensed by cold, like the vapour of water, and other fluids, and therefore may be very properly called an acid air, or more restrictively, the marine acid air.

This elastic acid vapour, or acid air, extinguishes flame, and is much heavier than common air; but how much heavier, will not be easy to ascertain. A cylindrical glass vessel, about three fourths of an inch in diameter, and four inches deep, being filled with it, and turned upside down, a lighted candle may be let down into it more than twenty times before it will burn at the bottom. It is pleasing to observe the colour of the flame in this experiment; for both before the candle goes out, and also when it is first lighted again, it burns with a beautiful green, or rather light-blue flame, such as is seen when common salt is thrown into the fire.

When this air is all expelled from any quantity of spirit of salt, which is easily perceived by the subsequent vapour being condensed by cold, the remainder is a very weak acid, barely capable of dissolving iron.

Being now in the possession of a new subject of experiments, viz. an elastic acid vapour, in the form of a permanent air, easily procured, and effectually confined by glass and quicksilver, with which it did not seem to have any affinity; I immediately began to introduce a variety of substances to it; in order to ascertain its peculiar properties and affinities, and also the properties of those other bodies with respect to it.

Beginning with water, which, from preceding observations, I knew would imbibe it, and become impregnated with it; I found that 2-1/2 grains of rain-water absorbed three ounce measures of this air, after which it was increased one third in its bulk, and weighed twice as much as before; so that this concentrated vapour seems to be twice as heavy as rain-water: Water impregnated with it makes the strongest spirit of salt that I have seen, dissolving iron with the most rapidity. Consequently, two thirds of the best spirit of salt is nothing more than mere phlegm or water.

Iron filings, being admitted to this air, were dissolved by it pretty fast, half of the air disappearing, and the other half becoming inflammable air, not absorbed by water. Putting chalk to it, fixed air was produced.

I had not introduced many substances to this air, before I discovered that it had an affinity with phlogiston, so that it would deprive other substances of it, and form with it such an union as constitutes inflammable air; which seems to shew, that inflammable air universally consists of the union of some acid vapour with phlogiston.

Inflammable air was produced, when to this acid air I put spirit of wine, oil of olives, oil of turpentine, charcoal, phosphorus, bees-wax, and even sulphur. This last observation, I own, surprized me; for, the marine acid being reckoned the weakest of the three mineral acids, I did not think that it had been capable of dislodging the oil of vitriol from this substance; but I found that it had the very same effect both upon alum and nitre; the vitriolic acid in the former case, and the nitrous in the latter, giving place to the stronger vapour of spirit of salt.

The rust of iron, and the precipitate of nitrous air made from copper, also imbibed this air very fast, and the little that remained of it was inflammable air; which proves, that these calces contain phlogiston. It seems also to be pretty evident, from this experiment, that the precipitate above mentioned is a real calx of the metal, by the solution of which the nitrous air is generated.

As some remarkable circumstances attend the absorption of this acid air, by the substances above-mentioned, I shall briefly mention them.

Spirit of wine absorbs this air as readily as water itself, and is increased in bulk by that means. Also, when it is saturated, it dissolves iron with as much rapidity, and still continues inflammable.

Oil of olives absorbs this air very slowly, and at the same time, it turns almost black, and becomes glutinous. It is also less miscible with water, and acquires a very disagreeable smell. By continuing upon the surface of the water, it became white, and its offensive smell went off in a few days.

Oil of turpentine absorbed this air very fast, turning brown, and almost black. No inflammable air was formed, till I raised more of the acid air than the oil was able to absorb, and let it stand a considerable time; and still the air was but weakly inflammable. The same was the case with the oil of olives, in the last mentioned experiment; and it seems to be probable, that, the longer this acid air had continued in contact with the oil, the more phlogiston it would have extracted from it. It is not wholly improbable, but that, in the intermediate state, before it becomes inflammable air, it may be nearly of the nature of common air.

Bees-wax absorbed this air very slowly. About the bigness of a hazel-nut of the wax being put to three ounce measures of the acid air, the air was diminished one half in two days, and, upon the admission of water, half of the remainder also disappeared. This air was strongly inflammable.

Charcoal absorbed this air very fast. About one fourth of it was rendered immiscible in water, and was but weakly inflammable.

A small bit of phosphorus, perhaps about half a grain, smoked, and gave light in the acid air, just as it would have done in common air confined. It was not sensibly wasted after continuing about twelve hours in that state, and the bulk of the air was very little diminished. Water being admitted to it absorbed it as before, except about one fifth of the whole. It was but weakly inflammable.

Putting several pieces of sulphur to this air, it was absorbed but slowly. In about twenty-four hours about one fifth of the quantity had disappeared; and water being admitted to the remainder, very little more was absorbed. The remainder was inflammable, and burned with a blue flame.

Notwithstanding the affinity which this acid air appears to have with phlogiston, it is not capable of depriving all bodies of it. I found that dry wood, crusts of bread, and raw flesh, very readily imbibed this air, but did not part with any of their phlogiston to it. All these substances turned very brown, after they had been some time exposed to this air, and tasted very strongly of the acid when they were taken out; but the flesh, when washed in water, became very white, and the fibres easily separated from one another, even more than they would have done if it had been boiled or roasted[9].

When I put a piece of saltpetre to this air it was presently surrounded with a white fume, which soon filled the whole vessel, exactly like the fume which bursts from the bubbles of nitrous air, when it is generated by a vigorous fermentation, and such as is seen when nitrous air is mixed with this acid air. In about a minute, the whole quantity of air was absorbed, except a very little, which might be the common air that had lodged upon the surface of the spirit of salt within the phial.

A piece of alum exposed to this air turned yellow, absorbed it as fast as the saltpetre had done, and was reduced by it to the form of a powder. Common salt, as might be expected, had no effect whatever on this marine acid air.

I had also imagined, that if air diminished by the processes above-mentioned was affected in this manner, in consequence of its being saturated with phlogiston, a mixture of this acid air might imbibe that phlogiston, and render it wholesome again; but I put about one fourth of this air to a quantity of air in which metals had been calcined, without making any sensible alteration in it. I do not, however, infer from this, that air is not diminished by means of phlogiston, since the common air, like some other substances, may hold the phlogiston too fast, to be deprived of it by this acid air.

I shall conclude my account of these experiments with observing, that the electric spark is visible in acid air, exactly as it is in common air; and though I kept making this spark a considerable time in a quantity of it, I did not perceive that any sensible alteration was made in it. A little inflammable air was produced, but not more than might have come from the two iron nails which I made use of in taking the sparks.

FOOTNOTES:

[9] It will be seen, in the second part of this work, that, in some of these processes, I had afterwards more success.



SECTION X.

MISCELLANEOUS OBSERVATIONS.

1. As many of the preceding observations relate to the vinous and putrefactive fermentations, I had the curiosity to endeavour to ascertain in what manner the air would be affected by the acetous fermentation. For this purpose I inclosed a phial full of small beer in a jar standing in water; and observed that, during the first two or three days, there was an increase of the air in the jar, but from that time it gradually decreased, till at length there appeared to be a diminution of about one tenth of the whole quantity.

During this time the whole surface of it was gradually covered with a scum, beautifully corrugated. After this there was an increase of the air till there was more than the original quantity; but this must have been fixed air, not incorporated with the rest of the mass; for, withdrawing the beer, which I found to be sour, after it had stood 18 or 20 days under the jar, and passing the air several times through cold water, the original quantity was diminished about one ninth. In the remainder a candle would not burn, and a mouse would have died presently.

The smell of this air was exceedingly pungent, but different from that of the putrid effluvium. A mouse lived perfectly well in this air, thus affected with the acetous fermentation; after it had stood several days mixed with four times the quantity of fixed air.

2. All the kinds of factitious air on which I have yet made the experiment are highly noxious, except that which is extracted from saltpetre, or alum; but in this even a candle burned just as in common air[10]. In one quantity which I got from saltpetre a candle not only burned, but the flame was increased, and something was heard like a hissing, similar to the decrepitation of nitre in an open fire. This experiment was made when the air was fresh made, and while it probably contained some particles of nitre, which would have been deposited afterwards. The air was extracted from these substances by heating them in a gun-barrel, which was much corroded and soon spoiled by the experiment. What effect this circumstance may have had upon the air I have not considered.

November 6, 1772, I had the curiosity to examine the state of a quantity of this air which had been extracted from saltpetre above a year, and which at first was perfectly wholesome; when, to my very great surprize, I found that it was become, in the highest degree, noxious. It made no effervescence with nitrous air, and a mouse died the moment it was put into it. I had not, however, washed it in rain-water quite ten minutes (and perhaps less time would have been sufficient) when I found, upon trial, that it was restored to its former perfectly wholesome state. It effervesced with nitrous air as much as the best common air ever does; and even a candle burned in it very well, which I had never before observed of any kind of noxious air meliorated by agitation in water. This series of facts, relating to air extracted from nitre, appear to me to be very extraordinary and important, and, in able hands, may lead to considerable discoveries.

3. There are many substances which impregnate common air in a very remarkable manner, but without making it noxious to animals. Among other things I tried volatile alkaline salts, and camphor; the latter of which I melted with a burning-glass, in air inclosed in a phial. The mouse, which was put into this air, sneezed and coughed very much, especially after it was taken out; but it presently recovered, and did not appear to have been sensibly injured.

4. Having made several experiments with a mixture of iron filings and brimstone, kneaded to a paste with water, I had the curiosity to try what would be the effect of substituting brass dust in the place of the iron filings. The result was, that when this mixture had stood about three weeks, in a given quantity of air, it had turned black, but was not increased in bulk. The air also was neither sensibly increased nor decreased, but the nature of it was changed; for it extinguished flame, it would have killed a mouse presently, and was not restored by fixed air, which had been mixed with it several days.

5. I have frequently mentioned my having, at one time, exposed equal quantities of different kinds of air in jars standing in boiled water. Common air in this experiment was diminished four sevenths, and the remainder extinguished flame. This experiment demonstrates that water does not absorb air equally, but that it decomposes it, taking one part, and leaving the rest. To be quite sure of this fact, I agitated a quantity of common air in boiled water, and when I had reduced it from eleven ounce measures to seven, I found that it extinguished a candle, but a mouse lived in it very well. At another time a candle barely went out when the air was diminished one third, and at other times I have found this effect lake place at other very different degrees of diminution.

This difference I attribute to the differences in the state of the water with respect to the air contained in it; for sometimes it had stood longer than at other times before I made use of it. I also used distilled-water, rain-water, and water out of which the air had been pumped, promiscuously with rain water. I even doubt, not but that, in a certain state of the water, there might be no sensible difference in the bulk of the agitated air, and yet at the end of the process it would extinguish a candle, air being supplied from the water in the place of that part of the common air which had been absorbed.

It is certainly a little extraordinary that the very same process should so far mend putrid air, as to reduce it to the standard of air in which candles have burned out; and yet that it should so far injure common and wholesome air as to reduce it to about the same standard: but so the fact certainly is. If air extinguish flame in consequence of its being previously saturated with phlogiston, it must, in this case, have been transferred from the water to the air, and it is by no means inconsistent with this hypothesis to suppose, that, if the air be over saturated with phlogiston, the water will imbibe it, till it be reduced to the same proportion that agitation in water would have communicated to it.

To a quantity of common air, thus diminished by agitation in water, till it extinguished a candle, I put a plant, but it did not so far restore it as that a candle would burn in it again; which to me appeared not a little extraordinary, as it did not seem to be in a worse state than air in which candles had burned out, and which had never failed to be restored by the same means.

I had no better success with a quantity of permanent air which I had collected from my pump-water. Indeed these experiments were begun before I was acquainted with that property of nitrous air, which makes it so accurate a measure of the goodness of other kinds of air; and it might perhaps be rather too late in the year when I made the experiments. Having neglected these two jars of air, the plants died and putrefied in both of them; and then I found the air in them both to be highly noxious, and to make no effervescence with nitrous air.

I found that a pint of my pump-water contained about one fourth of an ounce measure of air, one half of which was afterwards absorbed by standing in fresh pump-water. A candle would not burn in this air, but a mouse lived in it very well. Upon the whole, it seemed to be in about the same state as air in which a candle had burned out.

6. I once imagined that, by mere stagnation, air might become unfit for respiration, or at least the burning of candles; but if this be the case, and the change be produced gradually, it must require a long time for the purpose. For on the 22d of September 1772, I examined a quantity of common air, which had been kept in a phial, without agitation, from May 1771, and found it to be in no respect worse than fresh air, even by the test of the nitrous air.

7. The crystallization of nitre makes no sensible alteration in the air in which the process is made. For this purpose I dissolved as much nitre as a quantity of hot water would contain, and let it cool under a receiver, standing in water.

8. November 6, 1772, a quantity of inflammable air, which, by long keeping, had come to extinguish flame, I observed to smell very much like common air in which a mixture of iron filings and brimstone had stood. It was not, however, quite so strong, but it was equally noxious.

9. Bismuth and nickel are dissolved in the marine acid with the application of a considerable degree of heat; but little or no air is got from either of them; but, what I thought a little remarkable, both of them smelled very much like Harrowgate water, or liver of sulphur. This smell I have met with several times in the course of my experiments, and in processes very different from one another.

FOOTNOTES:

[10] Experiments, of which an account will be given in the second part of this work, make it probable, that though a candle burned even more than well in this air, an animal would not have lived in it. At the time of this first publication, however, I had no idea of this being possible in nature.



PART II.

Experiments and Observations made in the Year 1773, and the Beginning of 1774.



SECTION I.

Observations on ALKALINE AIR.

After I had made the discovery of the marine acid air, which the vapour of spirit of salt may properly enough be called, and had made those experiments upon it, of which I have given an account in the former part of this work, and others which I propose to recite in this part; it occurred to me, that, by a process similar to that by which this acid air is expelled from the spirit of salt, an alkaline air might be expelled from substances containing volatile alkali.

Accordingly I procured some volatile spirit of sal ammoniac, and having put it into a thin phial, and heated it with the flame of a candle, I presently found that a great quantity of vapour was discharged from it; and being received in a vessel of quicksilver, standing in a bason of quicksilver, it continued in the form of a transparent and permanent air, not at all condensed by cold; so that I had the same opportunity of making experiments upon it, as I had before on the acid air, being in the same favourable circumstances.

With the same ease I also procured this air from spirit of hartshorn, and sal volatile either in a fluid or solid form, i. e. from those volatile alkaline salts which are produced by the distillation of sal ammoniac with fixed alkalis. But in this case I soon found that the alkaline air I procured was not pure; for the fixed air, which entered into the composition of my materials, was expelled along with it. Also, uniting again with the alkaline air, in the glass tube through which they were conveyed, they stopped it up, and were often the means of bursting my vessels.

While these experiments were new to me, I imagined that I was able to procure this air with peculiar advantage and in the greatest abundance, either from the salts in a dry state, when they were just covered with water, or in a perfectly fluid state; for, upon applying a candle to the phials in which they were contained, there was a most astonishing production of air; but having examined it, I found it to be chiefly fixed air, especially after the first or second produce from the same materials; and removing my apparatus to a trough of water and using the water instead of quicksilver, I found that it was not presently absorbed by it.

This, however, appears to be an easy and elegant method of procuring fixed air, from a small quantity of materials, though there must be a mixture of alkaline air along with it; as it is by means of its combination with this principle only, that it is possible, that so much fixed air should be retained in any liquid. Water, at least, we know, cannot be made to contain much more than its own bulk of fixed air.

After this disappointment, I confined myself to the use of that volatile spirit of sal ammoniac which is procured by a distillation with slaked lime, which contains no fixed air; and which seems, in a general state, to contain about as much alkaline air, as an equal quantity of spirit of salt contains of the acid air.

Wanting, however, to procure this air in greater quantities, and this method being rather expensive, it occurred to me, that alkaline air might, probably, be procured, with the most ease and convenience, from the original materials, mixed in the same proportions that chemists had found by experience to answer the best for the production of the volatile spirit of sal ammoniac. Accordingly I mixed one fourth of pounded sal ammoniac, with three fourths of slaked lime; and filling a phial with the mixture, I presently found it completely answered my purpose. The heat of a candle expelled from this mixture a prodigious quantity of alkaline air; and the same materials (as much as filled an ounce phial) would serve me a considerable time, without changing; especially when, instead of a glass phial, I made use of a small iron tube, which I find much more convenient for the purpose.

As water soon begins to rise in this process, it is necessary, if the air is intended to be conveyed perfectly dry into the vessel of quicksilver, to have a small vessel in which this water (which is the common volatile spirit of sal ammoniac) may be received. This small vessel must be interposed between the vessel which contains the materials for the generation of the air, and that in which it is to be received, as d fig. 8.

This alkaline air being perfectly analogous to the acid air, I was naturally led to investigate the properties of it in the same manner, and nearly in the same order. From this analogy I concluded, as I presently found to be the fact, that this alkaline air would be readily imbibed by water, and, by its union with it, would form a volatile spirit of sal ammoniac. And as the water, when admitted to the air in this manner, confined by quicksilver, has an opportunity of fully saturating itself with the alkaline vapour, it is made prodigiously stronger than any volatile spirit of sal ammoniac that I have ever seen; and I believe stronger than it can be made in the common way.

In order to ascertain what addition, with respect to quantity and weight, water would acquire by being saturated with alkaline air, I put 1-1/4 grains of rain-water into a small glass tube, closed at one end with cement, and open at the other, the column of water measuring 7/10 of an inch; and having introduced it through the quicksilver into a vessel containing alkaline air, observed that it absorbed 7/8 of an ounce measure of the air, and had then gained about half a grain in weight, and was increased to 8-1/2 tenths of an inch in length. I did not make a second experiment of this kind, and therefore will not answer for the exactness of these proportions in future trials. What I did sufficiently answered my purpose, in a general view of the subject.

When I had, at one time, saturated a quantity of distilled water with alkaline air, so that a good deal of the air remained unabsorbed on the surface of the water, I observed that, as I continued to throw up more air, a considerable proportion of it was imbibed, but not the whole; and when I had let the apparatus stand a day, much more of the air that lay on the surface was imbibed. And after the water would imbibe no more of the old air, it imbibed new. This shews that water requires a considerable time to saturate itself with this kind of air, and that part of it more readily unites with water than the rest.

The same is also, probably, the case with all the kinds of air with which water can be impregnated. Mr. Cavendish made this observation with respect to fixed air, and I repeated the whole process above-mentioned with acid air, and had precisely the same result. The alkaline water which I procured in this experiment was, beyond comparison, stronger to the smell, than any spirit of sal ammoniac that I had seen.

This experiment led me to attempt the making of spirit of sal ammoniac in a larger quantity, by impregnating distilled water with this alkaline air. For this purpose I filled a piece of a gun-barrel with the materials above-mentioned, and luted to the open end of it a small glass tube, one end of which was bent, and put within the mouth of a glass vessel, containing a quantity of distilled water upon quicksilver, standing in a bason of quicksilver, as in fig. 7. In these circumstances the heat of the fire, applied gradually, expelled the alkaline air, which, passing through the tube, and the quicksilver, came at last to the water, which, in time, became fully saturated with it.

By this means I got a very strong alkaline liquor, from which I could again expel the alkaline air which I had put into it, whenever it happened to be more convenient to me to get it in that manner. This process may easily be performed in a still larger way; and by this means a liquor of the same nature with the volatile spirit of sal ammoniac, might be made much stronger, and much cheaper, than it is now made.

Having satisfied myself with respect to the relation that alkaline air bears to water, I was impatient to find what would be the consequence of mixing this new air with the other kinds with which I was acquainted before, and especially with acid air; having a notion that these two airs, being of opposite natures, might compose a neutral air, and perhaps the very same thing with common air. But the moment that these two kinds of air came into contact, a beautiful white cloud was formed, and presently filled the whole vessel in which they were contained. At the same time the quantity of air began to diminish, and, at length, when the cloud was subsided, there appeared to be formed a solid while salt, which was found to be the common sal ammoniac, or the marine acid united to the volatile alkali.

The first quantity that I produced immediately deliquesced, upon being exposed to the common air; but if it was exposed in a very dry and warm place, it almost all evaporated, in a white cloud. I have, however, since, from the same materials, produced the salt above-mentioned in a state not subject to deliquesce or evaporate. This difference, I find, is owing to the proportion of the two kinds of air in the compound. It is only volatile when there is more than a due proportion of either of the constituent parts. In these cases the smell of the salts is extremely pungent, but very different from one another; being manifestly acid, or alkaline, according to the prevalence of each of these airs respectively.

Nitrous air admitted to alkaline air likewise occasioned a whitish cloud, and part of the air was absorbed; but it presently grew clear again; leaving only a little dimness on the sides of the vessel. This, however, might be a kind of salt, formed by the union of the two kinds of air. There was no other salt formed that I could perceive. Water being admitted to this mixture of nitrous and alkaline air presently absorbed the latter, and left the former possessed of its peculiar properties.

Fixed air admitted to alkaline air formed oblong and slender crystals, which crossed one another, and covered the sides of the vessel in the form of net-work. These crystals must be the same thing with the volatile alkalis which chemists get in a solid form, by the distillation of sal ammoniac with fixed alkaline salts.

Inflammable air admitted to alkaline air exhibited no particular appearance. Water, as in the former experiment, absorbed the alkaline air, and left the inflammable air as it was before. It was remarkable, however, that the water which was admitted to them became whitish, and that this white cloud settled, in the form of a white powder, to the bottom of the vessel.

Alkaline air mixed with common air, and standing together several days, first in quicksilver, and then in water (which absorbed the alkaline air) it did not appear that there was any change produced in the common air: at least it was as much diminished by nitrous air as before. The same was the case with a mixture of acid air and common air.

Having mixed air that had been diminished by the fermentation of a mixture of iron filings and brimstone with alkaline air, the water absorbed the latter, but left the former, with respect to the test of nitrous air (and therefore, as I conclude, with respect to all its properties) the same that it was before.

Spirit of wine imbibes alkaline air as readily as water, and seems to be as inflammable afterwards as before.

Alkaline air contracts no union with olive oil. They were in contact almost two days, without any diminution of the air. Oil of turpentine, and essential oil of mint, absorbed a very small quantity of alkaline air, but were not sensibly changed by it.

Ether, however, imbibed alkaline air pretty freely; but it was afterwards as inflammable as before, and the colour was not changed. It also evaporated as before, but I did not attend to this last circumstance very accurately.

Sulphur, nitre, common salt, and flints, were put to alkaline air without imbibing any part of it; but charcoal, spunge, bits of linen cloth, and other substances of that nature, seemed to condense this air upon their surfaces; for it began to diminish immediately upon their being put to it; and when they were taken out the alkaline smell they had contracted was so pungent as to be almost intolerable, especially that of the spunge. Perhaps it might be of use to recover persons from swooning. A bit of spunge, about as big as a hazel nut, presently imbibed an ounce measure of alkaline air.

A piece of the inspissated juice of turnsole was made very dry and warm, and yet it imbibed a great quantity of the air; by which it contracted a most pungent smell, but the colour of it was not changed.

Alum undergoes a very remarkable change by the action of alkaline air. The outward shape and size remain the same, but the internal structure is quite changed, becoming opaque, beautifully white, and, to appearance, in all respects, like alum which had been roasted; and so as not to be at all affected by a degree of heat that would have reduced it to that state by roasting. This effect is produced slowly; and if a piece of alum be taken out of alkaline air before the operation is over, the inside will be transparent, and the outside, to an equal thickness, will be a white crust.

I imagine that the alkaline vapour seizes upon the water that enters into the constitution of crude alum, and which would have been expelled by heat. Roasted alum also imbibes alkaline air, and, like the raw alum that has been exposed to it, acquires a taste that is peculiarly disagreeable.

Phosphorus gave no light in alkaline air, and made no lasting change in its dimensions. It varied, indeed, a little, being sometimes increased and sometimes diminished, but after a day and a night, it was in the same state as at the first. Water absorbed this air just as if nothing had been put to it.

Having put some spirit of salt to alkaline air, the air was presently absorbed, and a little of the white salt above-mentioned was formed. A little remained unabsorbed, and transparent, but upon the admission of common air to it, it instantly became white.

Oil of vitriol, also formed a white salt with alkaline air, and this did not rise in white fumes.

Acid air, as I have observed in my former papers, extinguishes a candle. Alkaline air, on the contrary, I was surprized to find, is slightly inflammable; which, however, seems to confirm the opinion of chemists, that the volatile alkali contains phlogiston.

I dipped a lighted candle into a tall cylindrical vessel, filled with alkaline air, when it went out three or four times successively; but at each time the flame was considerably enlarged, by the addition of another flame, of a pale yellow colour; and at the last time this light flame descended from the top of the vessel to the bottom. At another time, upon presenting a lighted candle to the mouth of the same vessel, filled with the same kind of air, the yellowish flame ascended two inches higher than the flame of the candle. The electric spark taken in alkaline air is red, as it is in common inflammable air.

Though alkaline air be inflammable, it appeared, by the following experiment, to be heavier than the common inflammable air, as well as to contract no union with it. Into a vessel containing a quantity of inflammable air, I put half as much alkaline air, and then about the same quantity of acid air. These immediately formed a white cloud, but it did not rise within the space that was occupied by the inflammable air; so that this latter had kept its place above the alkaline air, and had not mixed with it.

That alkaline air is lighter than acid air is evident from the appearances that attend the mixture, which are indeed very beautiful. When acid air is introduced into a vessel containing alkaline air, the white cloud which they form appears at the bottom only, and ascends gradually. But when the alkaline air is put to the acid, the whole becomes immediately cloudy, quite to the top of the vessel.

In the last place, I shall observe that alkaline air, as well as acid, dissolves ice as fast as a hot fire can do it. This was tried when both the kinds of air, and every instrument made use of in the experiment, had been exposed to a pretty intense frost several hours. In both cases, also, the water into which the ice was melted dissolved more ice, to a considerable quantity.



SECTION II.

Of COMMON AIR diminished and made noxious by various processes.

It will have been observed that, in the first publication of my papers, I confined myself chiefly to the narration of the new facts which I had discovered, barely mentioning any hypotheses that occurred to me, and never seeming to lay much stress upon them. The reason why I was so much upon my guard in this respect was, left, in consequence of attaching myself to any hypothesis too soon, the success of my future inquiries might be obstructed. But subsequent experiments having thrown great light upon the preceding ones and having confirmed the few conjectures I then advanced, I may now venture to speak of my hypotheses with a little less diffidence. Still, however, I shall be ready to relinquish any notions I may now entertain, if new facts should hereafter appear not to favour them.

In a great variety of cases I have observed that there is a remarkable diminution of common, or respirable air, in proportion to which it is always rendered unfit for respiration, indisposed to effervesce with nitrous air, and incapable of farther diminution from any other cause. The circumstances which produce this effect I had then observed to be the burning of candles, the respiration of animals, the putrefaction of vegetables or animal substances, the effervescence of iron filings and brimstone, the calcination of metals, the fumes of charcoal, the effluvia of paint made of white-lead and oil, and a mixture of nitrous air.

All these processes, I observed, agree in this one circumstance, and I believe in no other, that the principle which the chemists call phlogiston is set loose; and therefore I concluded that the diminution of the air was, in some way or other, the consequence of the air becoming overcharged with phlogiston,[11] and that water, and growing vegetables, tend to restore this air to a state fit for respiration, by imbibing the superfluous phlogiston. Several experiments which I have since made tend to confirm this supposition.

Common air, I find, is diminished, and rendered noxious, by liver of sulphur, which the chemists say exhales phlogiston, and nothing else. The diminution in this case was one fifth of the whole, and afterwards, as in other similar cases, it made no effervescence with nitrous air.

I found also, after Dr. Hales, that air is diminished by Homberg's pyrophorus.

The same effect is produced by firing gunpowder in air. This I tried by firing the gunpowder in a receiver half exhausted, by which the air was rather more injured than it would have been by candles burning in it.

Air is diminished by a cement made with one half common coarse turpentine and half bees-wax. This was the result of a very casual observation. Having, in an air-pump of Mr. Smeaton's construction, closed that end of the syphon-gage, which is exposed to the outward air, with this cement (which I knew would make it perfectly air-light) instead of sealing it hermetically; I observed that, in a course of time, the quicksilver in that leg kept continually rising, so that the measures I marked upon it were of no use to me; and when I opened that end of the tube, and closed it again, the same consequence always took place. At length, suspecting that this effect must have arisen from the bit of cement diminishing the air to which it was exposed, I covered all the inside of a glass tube with it, and one end of it being quite closed with the cement, I set it perpendicular, with its open end immersed in a bason of quicksilver; and was presently satisfied that my conjecture was well founded: for, in a few days, the quicksilver rose so much within the tube, that the air in the inside appeared to be diminished about one sixth.

To change this air I filled the tube with quicksilver, and pouring it out again, I replaced the tube in its former situation; when the air was diminished again, but not so fast as before. The same lining of cement diminished the air a third time. How long it will retain this power I cannot tell. This cement had been made several months before I made this experiment with it. I must observe, however, that another quantity of this kind of cement, made with a finer and more liquid turpentine, had not the power of diminishing air, except in a very small proportion. Also the common red cement has this property in the same small degree. Common air, however, which had been confined in a glass vessel lined with this cement about a month, was so far injured that a candle would not burn in it. In a longer time it would, I doubt not, have become thoroughly noxious.

Iron that has been suffered to rust in nitrous air diminishes common air very fast, as I shall have occasion to mention when I give a continuation of my experiments on nitrous air.

Lastly, the same effect, I find, is produced by the electric spark, though I had no expectation of this event when I made the experiment.

This experiment, however, and those which I have made in pursuance of it, has fully confirmed another of my conjectures, which relates to the manner in which air is diminished by being overcharged with phlogiston, viz. the phlogiston having a nearer affinity with some of the constituent parts of the air than the fixed air which enters into the composition of it, in consequence of which the fixed air is precipitated.

This I first imagined from perceiving that lime-water became turbid by burning candles over it, p. 44. This was also the case with lime-water confined in air in which an animal substance was putrefying, or in which an animal died, p. 79. and that in which charcoal was burned, p. 81. But, in all these cases, there was a possibility of the fixed air being discharged from the candle, the putrefying substance, the lungs of the animal, or the charcoal. That there is a precipitation of lime when nitrous air is mixed with common air, I had not then observed, but I have since found it to be the case.

That there was no precipitation of lime when brimstone was burned, I observed, p. 45. might be owing to the fixed air and the lime uniting with the vitriolic acid, and making a salt, which was soluble in water; which salt I, indeed, discovered by the evaporation of the water.

I also observed, p. 46, 105. that diminished air being rather lighter than common air is a circumstance in favour of the fixed, or the heavier part of the common air, having been precipitated.

It was upon this idea, together with others similar to it, that I took so much pains to mix fixed air with air diminished by respiration or putrefaction, in order to make it fit for respiration again; and I thought that I had, in general, succeeded to a considerable degree, p. 99, &c. I will add, also, what I did not mention before, that I once endeavoured, but without effect, to preserve mice alive in the same unchanged air, by supplying them with fixed air, when the air in which they were confined began to be injured by their respiration. Without effect, also, I confined for some months, a quantity of quick lime in a given quantity of common air, thinking it might extract the fixed air from it.

The experiments which I made with electricity were solely intended to ascertain what has often been attempted, but, as far as I know, had never been fully accomplished, viz. to change the blue colour of liquors, tinged with vegetable juices, red.

For this purpose I made use of a glass tube, about one tenth of an inch diameter in the inside, as in fig. 16. In one end of this I cemented a piece of wire b, on which I put a brass ball. The lower part from a was filled with water tinged blue, or rather purple, with the juice of turnsole, or archil. This is easily done by an air-pump, the tube being set in a vessel of the tinged water.

Things being thus prepared, I perceived that, after I had taken the electric spark, between the wire b, and the liquor at a, about a minute, the upper part of it began to look red, and in about two minutes it was very manifestly so; and the red part, which was about a quarter of an inch in length, did not readily mix with the rest of the liquor. I observed also, that if the tube lay inclined while I took the sparks, the redness extended twice as far on the lower side as on the upper.

The most important, though the least expected observation, however, was that, in proportion as the liquor became red, it advanced nearer to the wire, so that the space of air in which the sparks were taken was diminished; and at length I found that the diminution was about one fifth of the whole space; after which more electrifying produced no sensible effect.

To determine whether the cause of the change of colour was in the air, or in the electric matter, I expanded the air which had been diminished in the tube by means of an air-pump, till it expelled all the liquor, and admitted fresh blue liquor into its place; but after that, electricity produced no sensible effect, either on the air, or on the liquor; so that it was evident that the electric matter had decomposed the air, and had made it deposite something that was of an acid nature.

In order to determine whether the wire had contributed any thing to this effect, I used wires of different metals, iron, copper, brass, and silver; but the result was the very same with them all.

It was also the same when, by means of a bent glass tube, I made the electric spark without any wire at all, in the following manner. Each leg of the tube, fig. 19. stood in a bason of quicksilver; which, by means of an air-pump, was made to ascend as high as a, a, in each leg, while the space between a and b in each contained the blue liquor, and the space between b and b contained common air. Things being thus disposed, I made the electric spark perform the circuit from one leg to the other, passing from the liquor in one leg of the tube to the liquor in the other leg, through the space of air. The effect was, that the liquor, in both the legs, became red, and the space of air between them was contracted, as before.

Air thus diminished by electricity makes no effervescence with, and is no farther diminished by a mixture of nitrous air; so that it must have been in the highest degree noxious, exactly like air diminished by any other process.

In order to determine what the acid was, which was deposited by the air, and which changed the colour of the blue liquor, I exposed a small quantity of the liquor so changed to the common air, and found that it recovered its blue colour, exactly as water, tinged with the same blue, and impregnated with fixed air, will do. But the following experiment was still more decisive to this purpose. Taking the electric spark upon lime-water, instead of the blue liquor, the lime was precipitated as the air diminished.

From these experiments it pretty clearly follows, that the electric matter either is, or contains phlogiston; since it does the very same thing that phlogiston does. It is also probable, from these experiments, that the sulphureous smell, which is occasioned by electricity, being very different from that of fixed air, the phlogiston in the electric matter itself may contribute to it.

It was now evident that common air diminished by any one of the processes above-mentioned being the same thing, as I have observed, with air diminished by any other of them (since it is not liable to be farther diminished by any other) the loss which it sustains, in all the cases, is, in part, that of the fixed air which entered into its constitution. The fixed air thus precipitated from common air by means of phlogiston unites with lime, if any lime water be ready to receive it, unless there be some other substance at hand, with which it has a greater affinity, as the calces of metals.

If the whole of the diminution of common air was produced by the deposition of fixed air, it would be easy to ascertain the quantity of fixed air that is contained in any given quantity of common air. But it is evident that the whole of the diminution of common air by phlogiston is not owing to the precipitation of fixed air, because a mixture of nitrous air will make a great diminution in all kinds of air that are fit for respiration, even though they never were common air, and though nothing was used in the process for generating them that can be supposed to yield fixed air.

Indeed, it appears, from some of the experiments, that the diminution of some of these kinds of air by nitrous air is so great, and approaches so nearly to the quantity of the diminution of common air by the same process, as to shew that, unless they be very differently affected by phlogiston, very little is to be allowed to the loss of fixed air in the diminution of common air by nitrous air.

The kinds of air on which this experiment was made were inflammable air, nitrous air diminished by iron filings and brimstone, and nitrous air itself; all of which are produced by the solution of metals in acids; and also on common air diminished and made noxious, and therefore deprived of its fixed air by phlogistic processes; and they were restored to a great degree of purity by agitation in water, out of which its own air had been carefully boiled.

To five parts of inflammable air, which had been agitated in water till it was diminished about one half (at which time part of it fired with a weak explosion) I put one part of nitrous air, which diminished it one eighth of the whole. This was done in lime-water, without any precipitation of lime. To compare this with common air, I mixed the same quantity, viz. five parts of this, and one part of nitrous air: when considerable crust of lime was formed upon the surface of the lime water, though the diminution was very little more than in the former process. It is possible, however, that the common air might have taken more nitrous air before it was fully saturated, so as to begin to receive an addition to its bulk.

I agitated in water a quantity of nitrous air phlogisticated with iron filings and brimstone, and found it to be so far restored, that three fourths of an ounce measure of nitrous air being put to two ounce measures of it, made no addition to it.

But the most remarkable of these experiments is that which I made with nitrous air itself which I had no idea of the possibility of reducing to a state fit for respiration by any process whatever, at the time of my former publication on this subject. This air, however, itself, without any previous phlogistication, is purified by agitation in water till it is diminished by fresh nitrous air, and to a very considerable degree.

In a pretty long time I agitated nitrous air in water, supplying it from time to time with more, as the former quantity diminished, till only one eighteenth of the whole quantity remained; in which state it was so wholesome, that a mouse lived in two ounce measures of it more than ten minutes, without shewing any sign of uneasiness; so that I concluded it must have been about as good as air in which candles had burned out. After agitating it again in water, I put one part of fresh nitrous air to five parts of this air, and it was diminished one ninth part. I then agitated it a third time, and putting more nitrous air to it, it was diminished again in the same proportion, and so a fourth time; so that, by continually repeating the process, it would, I doubt not, have been all absorbed. These processes were made in lime-water, without forming any incrustation on the surface of it.

Lastly, I took a quantity of common air, which had been diminished and made noxious by phlogistic processes; and when it had been agitated in water, I found that it was diminished by nitrous air, though not so much as it would have been at the first. After cleansing it a second time, it was diminished again by the same means; and, after that, a third time; and thus there can be no doubt but that, in time, the whole quantity would have disappeared. For I have never found that agitation in water, deprived of its own air, made any addition to a quantity of noxious air; though, a priori, it might have been imagined that, as a saturation with phlogiston diminishes air, the extraction of phlogiston would increase the bulk of it. On the contrary, agitation in water always diminished noxious air a little; indeed, if water be deprived of all its own air, it is impossible to agitate any kind of air in it without some loss. Also, when noxious air has been restored by plants, I never perceived that it gained any addition to its bulk by that means. There was no incrustation of the lime-water in the above-mentioned experiment.

It is not a little remarkable, that those kinds of air which never had been common air, as inflammable air, phlogisticated nitrous air, and nitrous air itself, when rendered wholesome by agitation in water, should be more diminished by fresh nitrous air, than common air which had been made noxious, and restored by the same process; and yet, from the few trials that I have made, I could not help concluding that this is the case.

In this course of experiments I was very near deceiving myself, in consequence of transferring the nitrous air which I made use of in a bladder, in the manner described, p. 15. fig. 9. so as to conclude that there was a precipitation of lime in all the above-mentioned cases, and that even nitrous air itself produced that effect. But after repeated trials, I found that there was no precipitation of lime, except, in the first diminution of common air, when the nitrous air was transferred in a glass vessel.

That the calces of metals contain air, of some kind or other, and that this air contributes to the additional weight of the calces, above that of the metals from which they are made, had been observed by Dr. Hales; and Mr. Hartley had informed me, that when red-lead is boiled in linseed oil, there is a prodigious discharge of air before they incorporate. I had likewise found, that no weight is either gained or lost by the calcination of tin in a close glass vessel; but I purposely deferred making any more experiments on the subject, till we should have some weather in which I could make use of a large burning lens, which I had provided for that and other purposes; but, in the mean time, I was led to the discovery in a different manner.

Having, by the last-recited experiments, been led to consider the electric matter as phlogiston, or something containing phlogiston, I was endeavouring to revivify the calx of lead with it; when I was surprized to perceive a considerable generation of air. It occurred to me, that possibly this effect might arise from the heat communicated to the red-lead by the electric sparks, and therefore I immediately filled a small phial with the red-lead, and heating it with a candle, I presently expelled from it a quantity of air about four or five times the bulk of the lead, the air being received in a vessel of quicksilver. How much more air it would have yielded, I did not try.

Along with the air, a small quantity of water was likewise thrown out; and it immediately occurred to me, that this water and air together must certainly be the cause of the addition of weight in the calx. It still remained to examine what kind of air this was; but admitting water to it, I found that it was imbibed by it, exactly like fixed air, which I therefore immediately concluded it must be[12].

After this, I found that Mr. Lavoisier had completely discovered the same thing, though his apparatus being more complex, and less accurate than mine, he concluded that more of the air discharged from the calces of metals was immiscible with water than I found it to be. It appeared to me that I had never obtained fixed air more pure.

It being now pretty clearly determined, that common air is made to deposit the fixed air which entered into the constitution of it, by means of phlogiston, in all the cases of diminished air, it will follow, that in the precipitation of lime, by breathing into lime-water the fixed air, which incorporates with lime, comes not from the lungs, but from the common air, decomposed by the phlogiston exhaled from them, and discharged, after having been taken in with the aliment, and having performed its function in the animal system.

Thus my conjecture is more confirmed, that the cause of the death of animals in confined air is not owing to the want of any pabulum vitae, which the air had been supposed to contain, but to the want of a discharge of the phlogistic matter, with which the system was loaded; the air, when once saturated with it, being no sufficient menstruum to take it up.

The instantaneous death of animals put into air so vitiated, I still think is owing to some stimulus, which, by causing immediate, universal and violent convulsions, exhausts the whole of the vis vitae at once; because, as I have observed, the manner of their death is the very same in all the different kinds of noxious air.

To this section on the subject of diminished, and noxious air, or as it might have been called phlogisticated air, I shall subjoin a letter which I addressed to Sir John Pringle, on the noxious quality of the effluvia of putrid marshes, and which was read at a meeting of the Royal Society, December 16, 1773.

This letter which is printed in the Philosophical Transactions, Vol. 74, p. 90. is immediately followed by another paper, to which I would refer my reader. It was written by Dr. Price, who has so greatly distinguished himself, and done such eminent service to his country, and to mankind, by his calculations relating to the probabilities of human life, and was suggested by his hearing this letter read at the Royal Society. It contains a confirmation of my observations on the noxious effects of stagnant waters by deductions from Mr. Muret's account of the Bills of Mortality for a parish situated among marshes, in the district of Vaud, belonging to the Canton of Bern in Switzerland.

To Sir JOHN PRINGLE, Baronet.

DEAR SIR,

Having pursued my experiments on different kinds of air considerably farther, in several respects, than I had done when I presented the last account of them to the Royal Society; and being encouraged by the favourable notice which the Society has been pleased to take of them, I shall continue my communications on this subject; but, without waiting for the result of a variety of processes, which I have now going on, or of other experiments, which I propose to make, I shall, from time to time, communicate such detached articles, as I shall have given the most attention to, and with respect to which, I shall have been the most successful in my inquiries.

Since the publication of my papers, I have read two treatises, written by Dr. Alexander, of Edinburgh, and am exceedingly pleased with the spirit of philosophical inquiry, which they discover. They appear to me to contain many new, curious, and valuable observations; but one of the conclusions, which he draws from his experiments, I am satisfied, from my own observations, is ill founded, and from the nature of it, must be dangerous. I mean his maintaining, that there is nothing to be apprehended from the neighbourhood of putrid marshes.

I was particularly surprised, to meet with such an opinion as this, in a book inscribed to yourself, who have so clearly explained the great mischief of such a situation, in your excellent treatise on the diseases of the army. On this account, I have thought it not improper, to address to you the following observations and experiments, which I think clearly demonstrate the fallacy of Dr. Alexander's reasoning, indisputably establish your doctrine, and indeed justify the apprehensions of all mankind in this case.

I think it probable enough, that putrid matter, as Dr. Alexander has endeavoured to prove, will preserve other substances from putrefaction; because, being already saturated with the putrid effluvium, it cannot readily take any more; but Dr. Alexander was not aware, that air thus loaded with putrid effluvium is exceedingly noxious when taken into the lungs. I have lately, however, had an opportunity of fully ascertaining how very noxious such air is.

Happening to use at Calne, a much larger trough of water, for the purpose of my experiments, than I had done at Leeds, and not having fresh water so near at hand as I had there, I neglected to change it, till it turned black, and became offensive, but by no means to such a degree, as to deter me from making use of it. In this state of the water, I observed bubbles of air to rise from it, and especially in one place, to which some shelves, that I had in it, directed them; and having set an inverted glass vessel to catch them, in a few days I collected, a considerable quantity of this air, which issued spontaneously from the putrid water; and putting nitrous air to it, I found that no change of colour or diminution ensued, so that it must have been, in the highest degree, noxious. I repeated the same experiment several times afterwards, and always with the same result.

After this, I had the curiosity to try how wholesome air would be affected by this water; when, to my real surprise, I found, that after only one minute's agitation in it, a candle would not burn in it; and, after three or four minutes, it was in the same state with the air, which had issued spontaneously from the same water.

I also found, that common air, confined in a glass vessel, in contact only with this water, and without any agitation, would not admit a candle to burn in it after two days.

These facts certainly demonstrate, that air which either arises from stagnant and putrid water, or which has been for some time in contact with it, must be very unfit for respiration; and yet Dr. Alexander's opinion is rendered so plausible by his experiments, that it is very possible that many persons may be rendered secure, and thoughtless of danger, in a situation in which they must necessarily breathe it. On this account, I have thought it right to make this communication as early as I conveniently could; and as Dr. Alexander appears to be an ingenuous and benevolent man, I doubt not but he will thank me for it.

That air issuing from water, or rather from the soft earth, or mud, at the bottom of pits containing water, is not always unwholesome, I have also had an opportunity of ascertaining. Taking a walk, about two years ago, in the neighbourhood of Wakefield, in Yorkshire, I observed bubbles of air to arise, in remarkably great plenty, from a small pool of water, which, upon inquiry, I was informed had been the place, where some persons had been boring the ground, in order to find coal. These bubbles of air having excited my curiosity, I presently returned, with a bason, and other vessels proper for my purpose, and having stirred the mud with a long stick, I soon got about a pint of this air; and, examining it, found it to be good, common air; at least a candle burned in it very well. I had not then discovered the method of ascertaining the goodness of common air, by a mixture of nitrous air. Previous to the trial, I had suspected that this air would have been found to be inflammable.

I shall conclude this letter with observing, that I have found a remarkable difference in different kinds of water, with respect to their effect on common air agitated in them, and which I am not yet able to account for. If I agitate common air in the water of a deep well, near my house in Calne, which is hard, but clear and sweet, a candle will not burn in it after three minutes. The same is the case with the rain-water, which I get from the roof of my house. But in distilled water, or the water of a spring-well near the house, I must agitate the air about twenty minutes, before it will be so much injured. It may be worth while, to make farther experiments with respect to this property of water.

In consequence of using the rain-water, and the well-water above mentioned, I was very near concluding, contrary to what I have asserted in this treatise, that common air suffers a decomposition by great rarefaction. For when I had collected a considerable quantity of air, which had been rarefied about four hundred times, by an excellent pump made for me by Mr. Smeaton, I always found, that if I filled my receivers with the water above mentioned, though I did it so gradually as to occasion as little agitation as possible, a candle would not burn in the air that remained in them. But when I used distilled water, or fresh spring-water, I undeceived myself.

I think myself honoured by the attention, which, from the first, you have given to my experiments, and am, with the greatest respect,

Dear Sir,

Your most obliged

Humble Servant,

London, 7 Dec. 1773.

J. PRIESTLEY.

POSTSCRIPT.

I cannot help expressing my surprize, that so clear and intelligible an account, of Mr. SMEATON'S air-pump, should have been before the public so long, as ever since the publication of the forty-seventh volume of the Philosophical Transactions, printed in 1752, and yet that none of our philosophical instrument-makers should use the construction. The superiority of this pump, to any that are made upon the common plan, is, indeed, prodigious. Few of them will rarefy more than 100 times, and, in a general way, not more than 60 or 70 times; whereas this instrument must be in a poor state indeed, if it does not rarefy 200 or 300 times; and when it is in good order, it will go as far as 1000 times, and sometimes even much farther than that; besides, this instrument is worked with much more ease, than a common air-pump, and either exhausts or condenses at pleasure. In short, to a person engaged in philosophical pursuits, this instrument is an invaluable acquisition. I shall have occasion to recite some experiments, which I could not have made, and which, indeed, I should hardly have dared to attempt, if I had not been possessed of such an air-pump as this. It is much to be wished, that some person of spirit in the trade would attempt the construction of an instrument, which would do great credit to himself, as well as be of eminent service to philosophy.

FOOTNOTES:

[11] On this account, if it was thought convenient to introduce a new term (or rather make a new application of a term already in use among chemists) it might not be amiss to call air that has been diminished, and made noxious by any of the processes above mentioned, or others similar to them, by the common appellation of phlogisticated air; and, if it was necessary, the particular process by which it was phlogisticated might be added; as common air phlogisticated by charcoal, air phlogisticated by the calcination of metals, nitrous air phlogisticated with the liver of sulphur, &c.

[12] Here it becomes me to ask pardon of that excellent philosopher Father Beccaria of Turin, for conjecturing that the phlogiston, with which he revivified metals, did not come from the electric matter itself, but from what was discharged from other pieces of metal with which he made the experiment. See History of Electricity, p. 277, &c. This revivification of metals by electricity completes the proof of the electric matter being, or containing phlogiston.



SECTION III.

Of NITROUS AIR.

Since the publication of my former papers I have given more attention to the subject of nitrous air than to any other species of air; and having been pretty fortunate in my inquiries, I shall be able to lay before my reader a more satisfactory account of the curious phenomena occasioned by it, and also of its nature and constitution, than I could do before, though much still remains to be investigated concerning it, and many new objects of inquiry are started.

With a view to discover where the power of nitrous air to diminish common air lay, I evaporated to dryness a quantity of the solution of copper in diluted spirit of nitre; and having procured from it a quantity of a green precipitate, I threw the focus of a burning-glass upon it, when it was put into a vessel of quicksilver, standing inverted in a bason of quicksilver. In this manner I procured air from it, which appeared to be, in all respects, nitrous air; so that part of the same principle which had escaped during the solution, in the form of air, had likewise been retained in it, and had not left it in the evaporation of the water.

With great difficulty I also procured a small quantity of the same kind of air from a solution of iron in spirit of nitre, by the same process.

Having, for a different purpose, fired some paper, which had been dipped in a solution of copper in diluted spirit of nitre, in nitrous air, I found there was a considerable addition to the quantity of it; upon which I fired some of the same kind of paper in quicksilver and presently observed that air was produced from it in great plenty. This air, at the first, seemed to have some singular properties, but afterwards I found that it was nothing more than a mixture of nitrous air, from the precipitate of the solution, and of inflammable air, from the paper; but that the former was predominant.

In the mixture of this kind of air with common air, in a trough of water which had been putrid, but which at that time seemed to have recovered its former sweetness (for it was not in the least degree offensive to the smell) a phenomenon sometimes occurred, which for a long time exceedingly delighted and puzzled me; but which was afterwards the means of letting me see much farther into the constitution of nitrous air than I had been able to see before.

When the diminution of the air was nearly completed, the vessel in which the mixture was made began to be filled with the most beautiful white fumes, exactly resembling the precipitation of some white substance in a transparent menstruum, or the falling of very fine snow; except that it was much thicker below than above, as indeed is the case in all chemical precipitations. This appearance continued two or three minutes.

At other times I went over the same process, as nearly as possible in the same manner, but without getting this remarkable appearance, and was several times greatly disappointed and chagrined, when I baulked the expectations of my friends, to whom I had described, and meant to have shewn it. This made me give all the attention I possibly could to this experiment, endeavouring to recollect every circumstance, which, though unsuspected at the time, might have contributed to produce this new appearance; and I took a great deal of pains to procure a quantity of this air from the paper above mentioned for the purpose, which, with a small burning lens, and an uncertain sun, is not a little troublesome. But all that I observed for some time was, that I stood the best chance of succeeding when I warmed the vessel in which the mixture was made, and agitated the air during the effervescence.

Finding, at length, that, with the same preparation and attentions, I got the same appearance from a mixture of nitrous and common air in the same trough of water, I concluded that it could not depend upon any thing peculiar to the precipitate of the copper contained in the paper from which the air was procured, as I had at first imagined, but upon what was common to it, and pure nitrous air.

Afterwards, having, (with a view to observe whether any crystals would be formed by the union of volatile alkali, and nitrous air, similar to those formed by it and fixed air, as described by Mr. Smeth in his Dissertation on fixed Air) opened the mouth of a phial which was half filled with a volatile alkaline liquor, in a jar of nitrous air (in the manner described p. 11. fig. 4.) I had an appearance which perfectly explained the preceding. All that part of the phial which was above the liquor, and which contained common air, was filled with beautiful white clouds, as if some fine white powder had been instantly thrown into it, and some of these clouds rose within the jar of nitrous air. This appearance continued about a minute, and then intirely disappeared, the air becoming transparent.

Withdrawing the phial, and exposing it to the common air, it there also became turbid, and soon after the transparency returned. Introducing it again into the nitrous air, the clouds appeared as before. In this manner the white fumes, and transparency, succeeded each other alternately, as often as I chose to repeat the experiment, and would no doubt have continued till the air in the jar had been thoroughly diluted with common air. These appearances were the same with any substance that contained volatile alkali, fluid or solid.

When, instead of the small phial, I used a large and tall glass jar, this appearance was truly fine and striking, especially when the water in the trough was very transparent. For I had only to put the smallest drop of a volatile alkaline liquor, or the smallest bit of the solid salt, into the jar, and the moment that the mouth of it was opened in a jar of nitrous air, the white clouds above mentioned began to be formed at the mouth, and presently descended to the bottom, so as to fill the whole, were it ever so large, as with fine snow.

In considering this experiment, I soon perceived that this curious appearance must have been occasioned by the mixture of the nitrous and common air, and therefore that the white clouds must be nitrous ammoniac, formed by the acid of the nitrous air, set loose in the decomposition of it by common air, while the phlogiston, which must be another constituent part of nitrous air, entering the common air, is the cause of the diminution it suffers in this process; as it is the cause of a similar diminution, in a variety of other processes.