Discovery of Oxygen, Part 2

by Carl Wilhelm Scheele

90. Seventh Experiment.—(a.) I put 2 ounces of nitre into a small glass retort upon glowing coals, and attached a large bladder softened with water (§ 35), and allowed the nitre to boil until I had received 3⁄4 of a quart of fire-air in the bladder. I then tied up the bladder and separated it from the retort; I then placed a tube in its opening, and after I had completely emptied my lungs, I began to respire air from this bladder (§ 84). This proceeded very well, and I was able to make 40 inspirations before it became difficult for me; eventually I expelled the air again from my lungs as completely as possible. It did not seem to have diminished particularly, and when I filled a bottle with it and introduced a burning candle, this still burned. I then began to respire this air anew, and was able to make 16 more inspirations. It now extinguished the flame, but I found only some traces of aerial acid in it. (b.) I was surprised that I was not able the first time to take away from this air the property of allowing fire to burn in it; I thought that perhaps the great humidity prevented me from drawing this air into my lungs so often as was really possible. Accordingly I repeated the same experiment, only with this difference, that I put a handful of potashes into the bladder before the fire-air was driven into it. I then

began to draw this air into my lungs, and counted 65 inspirations before I was compelled to desist. But when I lowered a burning candle into this air, it still burned well, although only for a few seconds.

91. Eighth Experiment.—I closed the hole in the bottle at A (Fig. 5) with a cork, as also the tube B, and then filled the bottle with fire-air (§ 30, e.). Then I had at hand the glass C, in which I had placed 2 large bees, and had provided some honey for their stay. I opened the stopped-up tube, placed this glass over it as quickly as possible, and pressed it into the ring of pitch. I afterwards placed the whole in the dish D, which I had filled with milk of lime, and withdrew the cork at A. In this case I observed the milk of lime to rise a little into the bottle every day, and after 8 days had elapsed the bottle was almost completely filled with it, and the bees were dead.

92. Ninth Experiment.—Plants, however, will not grow noticeably in pure fire-air. I filled with this air a bottle capable of holding 16 ounces of water, and which contained 4 peas (§ 88). They got roots, but did not grow up at all; with milk of lime the twelfth part was absorbed. I then filled this air into another bottle which also contained 4 peas. After 14 days they had got roots, but also did not grow up, and with milk of lime likewise only the twelfth part was absorbed. I repeated this experiment 3 times more with the same air, and it was observed that the fourth and fifth times the peas had grown upwards a little. There still remained one-half of the whole air, and in this fire could still burn. There is no doubt that the whole quantity of fire-air could have been converted into aerial acid if I had continued the operation longer. It may also be observed that the peas act more strongly upon the fire-air when they send out roots than subsequently.

93. Hence it is the fire-air by means of which the circulation of the blood and of the juices in animals and plants is so fully maintained. Still it is a peculiar circumstance that blood and the lungs have not such action upon fire-air as insects and plants have, for the latter convert it into aerial acid, and the former into vitiated air (§§ 29, 89, 90). It is not so easy to furnish the reason for this, yet I will risk it. 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. This they again give up. The objection that so great a quantity of aerial acid is nevertheless obtained in the destruction of plants, and that, consequently, these must attract the aerial acid, has no weight, since otherwise the air in my vessels in which the peas were contained must have become for the most part lost, which, however, did not take place.... If plants abstract the phlogiston from the air, the aerial acid must be lighter. But experiment shows me the opposite; I found it, after careful weighing, somewhat heavier, but this is not contrary to my opinion; as it is known that all acids retain water strongly, the aerial acid must possess the same property, and this may consequently cause the most of the weight. If all this is accurate, another question then arises: Why do not blood and the lungs likewise convert fire-air into such an aerial acid? I take the liberty here also of giving my opinion of this, for how would all these laboriously executed experiments help me if I had not

the hope of coming by means of them nearer to my ultimate object, the truth? Phlogiston, which makes most substances with which it unites liquid as well as mobile and elastic, must have the same effect upon blood. The globules of blood must attract it from the air through the small pores of the lungs. By this union they become separated from one another, and are consequently made more liquid. They then appear bright red (§ 89). They must, however, give this attracted phlogiston up again during the circulation, and in consequence, be placed in a condition to absorb the inflammable substance anew from the air at that place where they are in the most intimate contact with it, that is, in the lungs. Where this phlogiston has gone to during the circulation of the blood, I leave to others to ascertain. 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. But that the blood really attracts the inflammable substance I have additional experiment to prove, since I have removed phlogiston by help of my lungs from inflammable air, and have converted this into vitiated air.

I filled a bladder with the air which one obtains from iron filings and vitriolic acid (§ 30, c.), and respired it in the manner previously described (§ 84). I was only able to inhale it 20 times, and after I had somewhat recovered, I expelled the air once more from my lungs as completely as possible, and again inhaled this inflammable air: after 10 inhalations I was compelled to desist from it, and observed that it could no longer be kindled, and also

would not unite with lime water. In one word it was a vitiated air.

I kept a piece of sulphur in continuous ebullition over the fire in a retort, capable of holding 12 ounces of water, with an empty bladder attached in place of a receiver, the retort also placed so that the sulphur which rose into the neck could run back again. After all had become cold, I found the air neither increased nor diminished: it smelt slightly hepatic, and extinguished a burning candle. I shall prove further on that sulphur can unite with more phlogiston; and it seems to me to follow from this experiment that something inflammable from the air had deposited itself upon the sulphur, and that the air had thereby acquired the property of a vitiated air. It is, however, also remarkable that other bodies which attract the inflammable substance more strongly, as for example, the fuming acid of nitre, do not abstract it from the air. It is likewise strange that I was able to inhale the inflammable air into my lungs only 20 times; and I observe here as something peculiar that, if I mistake not, I became very warm a quarter of an hour afterwards. 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. I likewise powdered finely some iron filings which had been fused together with excess of sulphur, moistened this with water, and preserved it in a bottle which was filled with aerial acid: but with the same result. After 2 two days the aerial acid was almost entirely absorbed. This philosopher also says