CHAPTER XXV.
OXYGEN.
"We were saying that oxygen----" cried Miss Miette, with a smile, thatevening, after dinner, seeing that Monsieur Roger had completelyforgotten his promise.
"Yes," Monsieur Dalize hastened to add, as he wished to distract hisfriend from sad thoughts; "yes, my dear Roger, we were saying thatoxygen----"
"Is a gas," continued Monsieur Roger, good-humoredly. "Yes, it is agas; and Miette, I suppose, will want to ask me, 'What is gas?'"
"Certainly," said Miette.
"Well, it is only recently that we have found out, although the oldscientists, who called themselves alchemists, had remarked that besidesthose things that come within reach of our senses there also existssomething invisible, impalpable; and, as their scientific methods didnot enable them to detect this thing, they had considered it a portionof the spirit land; and indeed some of the names which they adoptedunder this idea still remain in common use. Don't we often call alcohol'spirits of wine'? As these ancients did not see the air whichsurrounded them, it was difficult for them to know that men live in anocean of gas, in the same way as fish live in water; and they could notimagine that air is a matter just as much as water is. You remember thatuniversal gravitation was discovered through----"
"The fall of an apple," said Miette.
"Yes; and that was something that every one knew; it was a very commonfact that an apple would fall. Well, it was another common fact, anotherwell-known thing, which enabled the Fleming Van Helmont to discover inthe seventeenth century the real existence of gases, or at least of agas. Van Helmont, one winter evening, was struck by the differencebetween the bulk of the wood which burned on his hearth and the bulk ofthe ashes left by the wood after its combustion. He wished to examineinto this phenomenon, and he made some experiments. He readily foundthat sixty-two pounds of charcoal left, after combustion, only one poundof ashes. Now, what had become of the other sixty-one pounds? Reasonshowed him that they had been transformed into something invisible, or,according to the language of the times, into some aerial spirit. Thissomething Van Helmont called 'gaast,' which in Flemish means spirit, andwhich is the same word as our ghost. From the word gaast we have madeour word gas. The gas which Van Helmont discovered was, as we now know,carbonic acid. This scientist made another experiment which caused himto think a good deal, but which he could not explain. Now, we can repeatthis experiment, if it will give you any pleasure."
"Certainly," said Miette; "what shall I bring you?"
"Only two things,--a soup-plate and a candle."
Monsieur Roger lit the candle and placed it in the middle of thesoup-plate, which he had filled with water. Then he sought among theinstruments which had come with the air-pump, and found a little glassglobe. He placed the globe over the candle in the middle of the plate.Very soon, as if by a species of suction, the water of the plate rose inthe globe; then the candle went out.
"Can Miss Miette explain to me what she has just seen?" said MonsieurRoger.
Miette reflected, and said,--
"As the water rose in the globe, it must have been because the air hadleft the globe, since the water came to take its place."
"Yes," answered Monsieur Roger; "but the air could not leave the globe,as there is no opening in the globe on top, and below it there is water.It did not leave the globe, but it diminished. Now, tell me why itdiminished."
"Ah, I cannot tell you."
"Well, Van Helmont was in just your position. He could not know anythingabout the cause of this diminution, because he was ignorant of thecomposition of the air, which was not discovered until the next centuryby the celebrated French chemist Lavoisier. Now, this is how Lavoisierarrived at this important discovery. In the first place, he knew thatmetals, when they are calcined,--that is to say, when they are exposedto the action of fire,--increase in weight. This fact had been remarkedbefore his time by Dr. Jehan Rey, under the following circumstances: Adruggist named Brun came one day to consult the doctor. Rey asked to beallowed to feel his pulse.
"'But I am not sick,' cried the druggist.
"'Then what are you doing here?' said the doctor.
"'I come to consult you.'
"'Then you must be sick.'
"'Not at all. I come to consult you not for sickness, but in regard toan extraordinary thing which occurred in my laboratory.'
"'What was it?' asked Rey, beginning to be interested.
"'I had to calcine two pounds six ounces of tin. I weighed it carefullyand then calcined it, and after the operation I weighed it again bychance, and what was my astonishment to find two pounds and thirteenounces! Whence come these extra seven ounces? That is what I could notexplain to myself, and that is why I came to consult you.'
"Rey tried the same experiment again and again, and finally concludedthat the increase of weight came from combination with some part of theair.
"It is probable that this explanation did not satisfy the druggist; andyet the doctor was right. The increase came from the combination of themetal with that part of the air which Lavoisier called oxygen. Thatgreat chemist, after long study, declared that air was not a simplebody, but that it was a composite formed of two bodies, of twogases,--oxygen and nitrogen. This opinion, running counter as it did toall preconceived ideas, raised a storm around the head of the learnedman. He was looked upon as a fool, as an imbecile, as an ignoramus. Thatis the usual way.
"Lavoisier resolved to show to the unbelievers the two bodies whoseexistence he had announced. In the experiment of increasing the weightof metals during calcination, an experiment which has been oftenrepeated since Jehan Rey's time, either tin or lead had always beenused. Now, these metals, during calcination, absorb a good deal ofoxygen from the air, but, once they have absorbed it, they do not giveit up again. Lavoisier abandoned tin and lead, and made use of a liquidmetal called mercury. Mercury possesses not only the property ofcombining with the oxygen of the air when it is heated, but also that ofgiving back this oxygen as soon as the boiling-point is passed. Thechemist put mercury in a glass retort whose neck was very long and bentover twice. The retort was placed upon an oven in such a way that thebent end of the neck opened into the top of the globe full of air,placed in a tube also full of mercury. By means of a bent tube, a littleair had been sucked out of the globe in such a way that the mercury inthe tube, finding the pressure diminished, had risen a slight distancein the globe. In this manner the height of the mercury in the globe wasvery readily seen. The level of the mercury in the globe was notedexactly, as well as the temperature and the pressure. Everything beingnow ready for the experiment, Lavoisier heated the mercury in the retortto the boiling-point, and kept it on the fire for twelve days. Themercury became covered with red pellicles, whose number increasedtowards the seventh and eighth days; at the end of the twelfth day, asthe pellicles did not increase, Lavoisier discontinued the heat. Then hefound out that the mercury had risen in the globe much higher thanbefore he had begun the experiment, which indicated that the aircontained in the globe had diminished. The air which remained in theglobe had become a gas which was unfit either for combustion or forrespiration; in fact, it was nitrogen. But the air which haddisappeared from the globe, where had it gone to? What had become ofit?"
"Yes," said Miette, "it is like the air of our globe just now. Where hasit gone?"
"Wait a moment. Let us confine ourselves to Lavoisier's experiment."
"We are listening."
"Well, Lavoisier decided that the air which had disappeared could nothave escaped from the globe, because that was closed on all sides. Heexamined the mercury. It seemed in very much the same state. Whatdifference was there? None, excepting the red pellicles. Then it was inthe pellicles that he must seek for the air which had disappeared. Sothe red pellicles were taken up and heated in a little retort, furnishedwith a tube which could gather the gas; under the action of heat thepellicles were decomposed. Lavoisier obtained mercury and a gas. Thequantity of gas which he obtained represented the exact differenc
ebetween the original bulk of the air in the globe and the bulk of thegas which the globe held at the end of the experiment. ThereforeLavoisier had not been deceived. The air which had disappeared from theglobe had been found. This gas restored from the red pellicles was muchbetter fitted than the air of the atmosphere for combustion andrespiration. When a candle was placed in it, it burned with a dazzlinglight. A piece of charcoal, instead of consuming quietly, as in ordinaryair, burned with a flame and with a sort of crackling sound, and with alight so strong that the eye could hardly bear it. That gas was oxygen."
"And so the doubters were convinced," said Miette.
"Or at least they ought to have been," added Monsieur Dalize,philosophically.