Carl Wilhelm Scheele

“ It is known that the acids lose those properties by which they reveal themselves as acids, by the addition of the inflammable substance, as sulphur, the elastic acid of nitre, regulus of arsenic, sugar, and the like, plainly shew. I am inclined to believe that fire-air consists of a subtle acid substance united with phlogiston, and it is probable that all acids derive their origin from fire-air. Now, if this air penetrates into plants, these must attract the phlogiston, and consequently the acid, which manifests itself as aerial acid, must be produced. ”

“ Poor comfort for those who feel their greatest pleasure in the investigation of natural things! Far is he mistaken, who endeavours to confine chemistry, this noble science, within such narrow bounds! Others believe that earth and phlogiston are the things from which all material nature has derived its origin. ”

“ These are accordingly strange circumstances, that the air is not noticeably absorbed by animals endowed with lungs, contains in it very little aerial acid, and yet extinguishes fire. On the other hand insects and plants alter the air in exactly the same way, but still they convert the fourth part of it into aerial acid. Accordingly I was curious to know whether the fire-air was not that which was here converted into aerial acid, because in these latter experiments just as much of the air was converted into aerial acid as there was of fire-air present in it. ”

“ The attraction which the blood has for phlogiston cannot be so strong as that with which plants and insects attract it from the air, and then the blood cannot convert air into aerial acid; still it becomes converted into an air which lies midway between fire-air and aerial acid, that is, a vitiated air; for it unites neither with lime nor with water after the manner of fire-air and it extinguishes fire, after that of aerial acid. ”

“ As soon as the retort became red hot the bladder became expanded, and at the same time the reduced mercury rose into the neck. In this case no red sublimate arose as customarily takes place with that calx which is prepared by the acid of nitre. The air obtained was a pure fire-air. This is a remarkable circumstance, that the fire-air which had previously removed from the mercury its phlogiston in a slow calcination, gives this same phlogiston up to it again when the calx is simply made red-hot. ”

“ On the other hand, when one places a burning candle in the receiver filled with blood-red vapours, towards the end of the distillation when, as has been said, the mixture froths strongly, not only will it continue to burn, but this will take place with a much brighter light than in ordinary air. The same thing occurs when one attaches, at the close of the distillation, a receiver which is filled with an air in which fire will not burn, for, when this has been attached for half an hour, a candle will likewise continue to burn in the air. ”

“ The swelling up of peas in cold water is to be ascribed mainly to the fire-air present in the water. If a bottle is filled full of water and a few peas are placed in it, after 24 hours the water contains aerial acid it is true, but no fire-air. In water boiled and become cold, peas swell up only a little. ”

“ Fire must burn for a certain time in a given quantity of air. (2.) If, so far as can be seen, this fire does not produce during combustion any fluid resembling air, then, after the fire has gone out of itself, the quantity of air must be diminished between a third and a fourth part. (3.) It must not unite with common water. (4.) All kinds of animals must live for a certain time in a confined quantity of air. (5.) Seeds, as for example peas, in a given quantity of similarly confined air, must strike roots and attain a certain height with the aid of some water and of a moderate heat. ”

“ It is also to be observed that fire-air, vitiated by the lungs, extinguishes fire; why does not the aerial acid attract the phlogiston again? why not also the vitiated air? Mr. Priestley indeed has accomplished this, but it did not succeed with me however much I also wished it. He has converted aerial acid into wholesome air by means of a mixture of iron filings, sulphur, and some water. When I desired to repeat this experiment, the aerial acid was always absorbed by the iron filings. ”

“ It is known that freshly drawn blood, when it stands in the open air, assumes a fine red on the surface, and that the under portions likewise become red when they come into contact with the air. Does the air in this case undergo any alteration? I filled a flask one third part [Pg 39] with freshly drawn ox blood, closed it tightly with a bladder, and shook up the blood frequently. Eight hours afterwards I neither found aerial acid in this air, nor that its bulk was diminished; but the flame of a candle was immediately extinguished in it. ”

“ But since they see that the air so produced is endowed with properties quite different from common air, they conclude, without experimental proofs, that this air has united with foreign materials, and that it must be purified from these admixed foreign particles by agitation and filtration with various liquids. I believe that there would be no hesitation in accepting this opinion, if one could only demonstrate clearly by experiments that a given quantity of air is capable of being completely converted into fixed or other kind of air by the admixture of foreign materials ”

“ These experiments shew, therefore, that this fire-air is just that air by means of which fire burns in common air; only it is there mixed with a kind of air which seems to possess no attraction at all for the inflammable substance, and this it is which places some hindrance in the way of the otherwise rapid and violent inflammation. And in fact, if air consisted of nothing but fire-air, water would surely render small service in extinguishing outbreaks of fire. ”

“ I took a glass retort which was capable of holding 8 ounces of water, and distilled fuming acid of nitre according to the usual method. In the beginning the acid went over red, then it became colourless, and finally all became red again; as soon as I perceived the latter, I took away the receiver and tied on a bladder, emptied of air, into which I poured some thick milk of lime (§ 22) in order to prevent the corrosion of the bladder. I then proceeded with the distillation. The bladder began [Pg 23] to expand gradually. After this I permitted everything to cool, and tied up the bladder. ”

“ It owes its presence to organised bodies, destroyed by putrefaction or combustion.
5. Nothing has given philosophers more trouble for some years than just this delicate acid or so called fixed air. Indeed it is not surprising that the conclusions which one draws from the properties of this elastic acid are not favourable to all who are prejudiced by previously conceived opinions. These defenders of the Paracelsian [Pg 7] doctrine believe that the air is in itself unalterable; and, with Hales, that it really unites with substances thereby losing its elasticity ”

“ Not only have the claims of Scheele to the independent discovery of this gas never been disputed, but the valuable volume of "Letters and Memoranda" of Scheele, edited by Nordenskjöld, which was published in 1892, places it beyond doubt that Scheele had obtained oxygen by more than one method at least as early as Priestley's first isolation of the gas, although his printed account of the discovery only appeared about two years after Priestley's. The evidence of this has been found in Scheele's laboratory notes, which are still preserved in the Royal Academy of Science in Stockholm. ”

“ I then pour above it the acid diluted with water and press out the air as completely as possible; I finally tie up the bladder above at CC. I then untie the twine B, when the acid runs upon the chalk; it immediately drives out the aerial acid, whereupon the bladder must expand. (e.) When I require to get an air out of the bladder into a flask, glass, retort, or bottle, I fill such apparatus with water and place in it a tightly fitting cork; I then tie the bladder which contains the air, that is, the opening from C to D (Fig. 4) , very firmly over such bottle ”

“ How difficult it is, however, to carry out such operations with the greatest accuracy, can only be unknown to one who either has never undertaken this occupation, or at least has not done so with sufficient attention. ”

“ This air had all the properties of a pure fire-air.
33. Second Experiment.—When I distilled two parts of finely pulverised manganese with one part of the phosphorous acid of urine in the same way as is indicated in the preceding paragraph, I likewise obtained fire-air. ”