Of the Decomposition of Oxygen Gas by Sulphur, Phoſphorus, and of the Formation of Acids in general.
IN performing experiments, it is a neceſſary principle, which ought never to be deviated from, that they be ſimplified as much as poſſible, and that every circumſtance capable of rendering their reſults complicated be carefully removed. Wherefore, in the experiments which form the object of this chapter, we have never employed atmoſpheric air, which is not a ſimple ſubſtance. It is true, that the azotic gas, which forms a part of its mixture, appears to be merely paſſive during combuſtion and calcination ; but, beſides that it retards theſe operations very conſiderably, we are not certain but it may even alter their reſults in ſome circumſtances ; for which reaſon, I have thought it neceſſary to remove even this poſſible cauſe of doubt, by only making uſe of pure oxygen gas in the following experiments, which ſhow the effects produced by combuſtion in that gas ; and I ſhall advert to ſuch differences as take place in the reſults of theſe, when the oxygen gas, or pure vital air, is mixed, in different proportions, with azotic gas.
Having filled a bell-glaſs (A. Pl. IV. fig. of between five and ſix pints meaſure, with oxygen gas, I removed it from the water trough, where it was filled, into the quickſilver bath, by means of a ſhallow glaſs diſh ſlipped underneath, and having dried the mercury, I introduced 61-1/4 grains of Kunkel’s phoſphorus in two little China cups, like that repreſented at D, fig. 3. under the glaſs A ; and that I might ſet fire to each of the portions of phoſphorus ſeparately, and to prevent the one from catching fire from the other, one of the diſhes was covered with a piece of flat glaſs. I next raiſed the quickſilver in the bell-glaſs up to E F, by ſucking out a ſufficient portion of the gas by means of the ſyphon GHI. After this, by means of the crooked iron wire (fig. 16.), made red hot, I ſet fire to the two portions of phoſphorus ſucceſſively, firſt burning that portion which was not covered with the piece of glaſs. The combuſtion was extremely rapid, attended with a very brilliant flame, and conſiderable diſengagement of light and heat. In conſequence of the great heat induced, the gas was at firſt much dilated, but ſoon after the mercury returned to its level, and a conſiderable abſorption of gas took place; at the ſame time, the whole inſide of the glaſs became covered with white light flakes of concrete phoſphoric acid.
At the beginning of the experiment, the quantity of oxygen gas, reduced, as above directed, to a common ſtandard, amounted to 162 cubical inches; and, after the combuſtion was finiſhed, only 23-1/4 cubical inches, likewiſe reduced to the ſtandard, remained ; ſo that the quantity of oxygen gas abſorbed during the combuſtion was 138-3/4 cubical inches, equal to 69.375 grains.
A part of the phoſphorus remained unconſumed in the bottom of the cups, which being waſhed on purpoſe to Separate the acid, weighed about 16-1/4 grains ; ſo that about 45 grains of phoſphorus had been burned : But, as it is hardly poſſible to avoid an error of one or two grains, I leave the quantity ſo far qualified. Hence, as nearly 45 grains of phoſphorus had, in this experiment, united with 69.375 grains of oxygen, and as no gravitating matter could have eſcaped through the glaſs, we have a right to conclude, that the weight of the ſubſtance reſulting from the combuſtion in form of white flakes, muſt equal that of the phoſphorus and oxygen employed, which amounts to 114.375 grains. And we ſhall preſently find, that theſe flakes conſiſted entirely of a ſolid or concrete acid. When we reduce theſe weights to hundredth parts, it will be found, that 100 parts of Phoſphorus require 154 parts of oxygen for ſaturation, and that this combination will produce 254 parts of concrete phoſphoric acid, in form of white fleecy flakes.
This experiment proves, in the moſt convincing manner, that, at a certain degree of temperature, oxygen poſſeſſes a ſtronger elective attraction, or affinity, for phoſphorus than for caloric ; that, in conſequence of this, the phoſphorus attracts the baſe of oxygen gas from the caloric, which, being ſet free, ſpreads itſelf over the ſurrounding bodies. But, though this experiment be ſo far perfectly concluſive, it is not ſufficiently rigorous, as, in the apparatus deſcribed, it is impoſſible to aſcertain the weight of the flakes of concrete acid which are formed ; we can therefore only determine this by calculating the weights of oxygen and phoſphorus employed; but as, in phyſics, and in chemiſtry, it is not allowable to ſuppoſe what is capable of being ascertained by direct experiment, I thought it neceſſary to rep at this experiment, as follows, upon a larger ſcale, and by means of a different apparatus.
I took a large glaſs baloon (A. Pl. iv. fig. with an opening three inches diameter, to which was fitted a cryſtal ſtopper ground with emery, and pierced with two holes for the tubes yyy, xxx. Before ſhutting the baloon with its ſtopper, I introduced the ſupport BC, ſurmounted by the china cup D, containing 150 grs. of phoſphorus ; the ſtopper was then fitted to the opening of the baloon, luted with fat lute, and covered with ſlips of linen ſpread with quick lime and white of eggs : When the lute was perfectly dry, the weight of the whole apparatus was determined to within a grain, or a grain and a half. I next exhauſted the baloon, by means of an air pump applied to the tube xxx, and then introduced oxygen gas by means of the tube yyy, having a flop cock adapted to it. This kind of experiment is moſt readily and mod exactly performed by means of the hydro-pneumatic machine deſcribed by Mr Meuſnier and me in the Memoirs of the Academy for 1782, pag. 466. and explained in the latter part of this work, with ſeveral important additions and corrections ſince made to it by Mr Meuſnier. With this instrument we can readily aſcertain, in the moſt exact manner, both the quantity of oxygen gas introduced into the baloon, and the quantity conſumed during the courſe of the experiment.
When all things were properly diſpoſed, I ſet fire to the phoſphorus with a burning glaſs. The combuſtion was extremely rapid, accompanied with a bright flame, and much heat ; as the operation went on, large quantities of white flakes attached themſelves to the inner ſurface of the baloon, ſo that at laſt it was rendered quite opake. The quantity of theſe flakes at laſt became ſo abundant, that, although freſh oxygen gas was continually ſupplied, which ought to have ſupported the combuſtion, yet the phoſphorus was ſoon extinguiſhed. Having allowed the apparatus to cool completely, I firſt ascertained the quantity of oxygen gas employed, and weighed the baloon accurately, before it was opened. I next waſhed, dried, and weighed the ſmall quantity of phoſphorus remaining in the cup, on purpoſe to determine the whole quantity of phoſphorus conſumed in the experiment ; this reſiduum of the phoſphorus was of a yellow ochrey colour. It is evident, that by theſe ſeveral precautions, I could eaſily determine, 1ſt, the weight of the phoſphorus conſumed ; 2d, the weight of the flakes produced by the combuſtion ; and, 3d, the weight of the oxygen which had combined with the phoſphorus. This experiment gave very nearly the ſame reſults with the former, as it proved that the phoſphorus, during its combuſtion, had abſorbed a little more than one and a half its weight of oxygen ; and I learned with more certainty, that the weight of the new ſubſtance, produced in the experiment, exactly equalled the ſum of the weights of the phoſphorus conſumed, and oxygen abſorbed, which indeed was eaſily determinable a priori. If the oxygen gas employed be pure, the reſiduum after combuſtion is as pure as the gas employed; this proves that nothing eſcapes from the phoſphorus, capable of altering the purity of the oxygen gas, and that the only action of the phoſphorus is to ſeparate the oxygen from the caloric, with which it was before united.
I mentioned above, that when any combuſtible body is burnt in a hollow ſphere of ice, or in an apparatus properly conſtructed upon that principle, the quantity of ice melted during the combuſtion is an exact meaſure of the quantity of caloric diſengaged. Upon this head, the memoir given by M. de la Place and me, A°. 1780, p. 355, may be conſulted. Having ſubmitted the combuſtion of phoſphorus to this trial, we found that one pound of phoſphorus melted a little more than 100 pounds of ice during its combuſtion.
The combuſtion of phoſphorus ſucceeds equally well in atmoſpheric air as in oxygen gas, with this difference, that the combuſtion is vaſtly flower, being retarded by the large proportion of azotic gas mixed with the oxygen gas, and that only about one-fifth part of the air employed is abſorbed, becauſe as the oxygen gas only is abſorbed, the proportion of the azotic gas becomes ſo great toward the cloſe of the experiment, as to put an end to the combuſtion.
I have already ſhown, that phoſphorus is changed by combuſtion into an extremely light, white, flakey matter ; and its properties are entirely altered by this transformation : From being inſoluble in water, it becomes not only ſoluble, but ſo greedy of moiſture, as to attarct the humidity of the air with aſtoniſhing rapidity ; by this means it is converted into a liquid, conſiderably more denſe, and of more ſpecific gravity than water. In the ſtate of phoſphorus before combuſtion, it had ſcarcely any ſenſible taſte, by its union with oxygen it acquires an extremely ſharp and four taſte : in a word, from one of the claſs of combuſtible bodies, it is changed into an incombuſtible ſubſtance, and becomes one of thoſe bodies called acids.
This property of a combuſtible ſubſtance to be converted into an acid, by the addition of oxygen, we ſhall preſently find belongs to a great number of bodies : Wherefore, ſtrict logic requires that we ſhould adopt a common term for indicating all theſe operations which produce analogous reſults ; this is the true way to ſimplify the ſtudy of ſcience, as it would be quite impoſſible to bear all its ſpecifical details. in the memory, if they were not claſſically arranged. For this reaſon, we ſhall diſtinguiſh this converſion of phoſphorus into an acid, by its union with oxygen, and in general every combination of oxygen with a combuſtible ſubſtance, by the term of oxygenation : from which I ſhall adopt the verb to oxygenate, and of conſequence ſhall ſay, that in oxygenating phoſphorus we convert it into an acid.
Sulphur is likewiſe a combuſtible body, or, in other words, it is a body which poſſeſſes the power of decompoſing oxygen gas, by attracting the oxygen from the caloric with which it was combined. This can very eaſily be proved, by means of experiments quite ſimilar to thoſe we have given with phoſphorus ; but it is neceſſary to premiſe, that in theſe operations with ſulphur, the ſame accuracy of reſult is not to be expected as with phoſphorus ; becauſe the acid which is formed by the combuſtion of ſulphur is difficultly condenſible, and becauſe ſulphur burns with more difficulty, and is ſoluble in the different gaſſes. But I can ſafely aſſert, from my own experiments, that ſulphur in burning abſorbs oxygen gas ; that the reſulting acid is conſiderably heavier than the ſulphur burnt ; that its weight is equal to the ſum of the weights of the ſulphur which has been burnt, and of the oxygen abſorbed ; and, laſtly, that this acid is weighty, incombuſtible, and miſcible with water in all proportions : The only uncertainty remaining upon this head, is with regard to the proportions of ſulphur and of oxygen which enter into the compoſition of the acid.
Charcoal, which, from all our preſent knowledge regarding it, muſt be conſidered as a ſimple combuſtible body, has likewiſe the property of decompoſing oxygen gas, by abſorbing its baſe from the caloric : But the acid reſulting from this combuſtion does not condenſe in the common temperature ; under the preſſure of our atmoſphere, it remains in the ſtate of gas, and requires a large proportion of water to combine with or be diſſolved in. This acid has, however, all the known properties of other acids, though in a weaker degree, and combines, like them, with all the baſes which are ſuſceptible of forming neutral ſalts.
The combuſtion of charcoal in oxygen gas, may be effected like that of phoſphorus in the bell-glaſs, (A. Pl. IV. fig. placed over mercury : but, as the heat of red hot iron is not ſufficient to ſet fire to the charcoal, we muſt add a ſmall morſel of tinder, with a minute particle of phoſphorus, in the ſame manner as directed in the experiment for the combuſtion of iron. A detailed account of this experiment will be found in the memoirs of the academy for 1781, p. 448. By that experiment it appears, that 28 parts by weight of charcoal require 72 parts of oxygen for ſaturation, and that the aëriform acid produced is preciſely equal in weight to the ſum of the weights of the charcoal and oxygen gas employed. This aëriform acid was called fixed or fixable air by the chemiſts who firſt discovered it ; they did not then know whether it was air reſembling that of the atmoſphere, or ſome other elaſtic fluid, vitiated and corrupted by combuſtion ; but ſince it is now aſcertained to be an acid, formed like all others by the oxygenation of its peculiar baſe, it is obvious that the name of fixed air is quite
By burning charcoal in the apparatus mentioned p. 60, Mr de la Place and I found that one lib. of charcoal melted 96 libs. 6 oz. of ice ; that, during the combuſtion, 2 libs. 9 oz. 1 gros. 10 grs. of oxygen were abſorbed, and that 3 libs. 9 oz. 1 gros. 10 grs. of acid gas were formed. This gas weighs 0.695 parts of a grain for each cubical inch, in the common ſtandard temperature and preſſure mentioned above, ſo that 34,242 cubical inches of acid gas are produced by the combuſtion of one pound of charcoal.
I might multiply theſe experiments, and Show by a numerous ſucceſſion of facts, that all acids are formed by the combuſtion of certain ſubſtances ; but I am prevented from doing ſo in place, by the plan which I have laid down, of proceeding only from facts already aſcertained, to ſuch as are unknown, and of drawing my examples only from circumſtances already explained. In the mean time, however, the three examples above cited may ſuffice for giving a clear and accurate conception of the manner in which acids are formed. By theſe it may be clearly ſeen, that oxygen is an element common to them all, which conſtitutes their acidity ; and that they differ from each other, according to the nature of the oxygenated or acidified ſubſtance. We muſt therefore, in every acid, carefully diſtinguiſh between the acidifiable, baſe, which Mr de Morveau calls the radical, and the acidifiing principle or oxygen.
* It may be proper to remark, though here omitted by the author, that, in conformity with the general principles of the new nomenclature, this acid is by Mr Lavoiſier and his coleagues called the carbonic acid, and when in the aëriform ſtate carbonic acid gas. E.