OXYGEN.
"We were saying that oxygen----" cried Miss Miette, with a smile, that
evening, after dinner, seeing that Monsieur Roger had completely
forgotten his promise.
"Yes," Monsieur Dalize hastened to add, as he wished to distract his
friend from sad thoughts; "yes, my dear Roger, we were saying that
oxygen----"
"Is a gas," continued Monsieur Roger, good-humoredly. "Yes, it is a
gas; 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 old
scientists, who called themselves alchemists, had remarked that besides
those things that come within reach of our senses there also exists
something invisible, impalpable; and, as their scientific methods did
not enable them to detect this thing, they had considered it a portion
of the spirit land; and indeed some of the names which they adopted
under this idea still remain in common use. Don't we often call alcohol
'spirits of wine'? As these ancients did not see the air which
surrounded them, it was difficult for them to know that men live in an
ocean of gas, in the same way as fish live in water; and they could not
imagine that air is a matter just as much as water is. You remember that
universal gravitation was discovered through----"
"The fall of an apple," said Miette.
"Yes; and that was something that every one knew; it was a very common
fact that an apple would fall. Well, it was another common fact, another
well-known thing, which enabled the Fleming Van Helmont to discover in
the seventeenth century the real existence of gases, or at least of a
gas. Van Helmont, one winter evening, was struck by the difference
between the bulk of the wood which burned on his hearth and the bulk of
the ashes left by the wood after its combustion. He wished to examine
into this phenomenon, and he made some experiments. He readily found
that sixty-two pounds of charcoal left, after combustion, only one pound
of ashes. Now, what had become of the other sixty-one pounds? Reason
showed him that they had been transformed into something invisible, or,
according to the language of the times, into some aerial spirit. This
something Van Helmont called 'gaast,' which in Flemish means spirit, and
which is the same word as our ghost. From the word gaast we have made
our word gas. The gas which Van Helmont discovered was, as we now know,
carbonic acid. This scientist made another experiment which caused him
to think a good deal, but which he could not explain. Now, we can repeat
this 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 the
soup-plate, which he had filled with water. Then he sought among the
instruments which had come with the air-pump, and found a little glass
globe. 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 in
the globe; then the candle went out.
"Can Miss Miette explain to me what she has just seen?" said Monsieur
Roger.
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Miette reflected, and said,--
"As the water rose in the globe, it must have been because the air had
left 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 it
diminished."
"Ah, I cannot tell you."
"Well, Van Helmont was in just your position. He could not know anything
about the cause of this diminution, because he was ignorant of the
composition of the air, which was not discovered until the next century
by the celebrated French chemist Lavoisier. Now, this is how Lavoisier
arrived at this important discovery. In the first place, he knew that
metals, when they are calcined,--that is to say, when they are exposed
to the action of fire,--increase in weight. This fact had been remarked
before his time by Dr. Jehan Rey, under the following circumstances: A
druggist named Brun came one day to consult the doctor. Rey asked to be
allowed 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 to
an 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 carefully
and then calcined it, and after the operation I weighed it again by
chance, and what was my astonishment to find two pounds and thirteen
ounces! Whence come these extra seven ounces? That is what I could not
explain to myself, and that is why I came to consult you.'
"Rey tried the same experiment again and again, and finally concluded
that the increase of weight came from combination with some part of the
air.
"It is probable that this explanation did not satisfy the druggist; and
yet the doctor was right. The increase came from the combination of the
metal with that part of the air which Lavoisier called oxygen. That
great chemist, after long study, declared that air was not a simple
body, but that it was a composite formed of two bodies, of two
gases,--oxygen and nitrogen. This opinion, running counter as it did to
all preconceived ideas, raised a storm around the head of the learned
man. He was looked upon as a fool, as an imbecile, as an ignoramus. That
is the usual way.
"Lavoisier resolved to show to the unbelievers the two bodies whose
existence he had announced. In the experiment of increasing the weight
of metals during calcination, an experiment which has been often
repeated since Jehan Rey's time, either tin or lead had always been
used. Now, these metals, during calcination, absorb a good deal of
oxygen from the air, but, once they have absorbed it, they do not give
it up again. Lavoisier abandoned tin and lead, and made use of a liquid
metal called mercury. Mercury possesses not only the property of
combining with the oxygen of the air when it is heated, but also that of
giving back this oxygen as soon as the boiling-point is passed. The
chemist put mercury in a glass retort whose neck was very long and bent
over twice. The retort was placed upon an oven in such a way that the
bent 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 little
air had been sucked out of the globe in such a way that the mercury in
the tube, finding the pressure diminished, had risen a slight distance
in the globe. In this manner the height of the mercury in the globe was
very readily seen. The level of the mercury in the globe was noted
exactly, as well as the temperature and the pressure. Everything being
now ready for the experiment, Lavoisier heated the mercury in the retort
to the boiling-point, and kept it on the fire for twelve days. The
mercury became covered with red pellicles, whose number increased
towards the seventh and eighth days; at the end of the twelfth day, as
the pellicles did not increase, Lavoisier discontinued the heat. Then he
found out that the mercury had risen in the globe much higher than
before he had begun the experiment, which indicated that the air
contained in the globe had diminished. The air which remained in the
globe had become a gas which was unfit either for combustion or for
respiration; in fact, it was nitrogen. But the air which had
disappeared from the globe, where had it gone to? What had become of
it?"
"Yes," said Miette, "it is like the air of our globe just now. Where has
it 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 not
have escaped from the globe, because that was closed on all sides. He
examined the mercury. It seemed in very much the same state. What
difference was there? None, excepting the red pellicles. Then it was in
the pellicles that he must seek for the air which had disappeared. So
the red pellicles were taken up and heated in a little retort, furnished
with a tube which could gather the gas; under the action of heat the
pellicles were decomposed. Lavoisier obtained mercury and a gas. The
quantity of gas which he obtained represented the exact difference
between the original bulk of the air in the globe and the bulk of the
gas which the globe held at the end of the experiment. Therefore
Lavoisier had not been deceived. The air which had disappeared from the
globe had been found. This gas restored from the red pellicles was much
better fitted than the air of the atmosphere for combustion and
respiration. When a candle was placed in it, it burned with a dazzling
light. A piece of charcoal, instead of consuming quietly, as in ordinary
air, burned with a flame and with a sort of crackling sound, and with a
light 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.
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