Part 24 (1/2)

”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 gla.s.s 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.

[Ill.u.s.tration]

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 circ.u.mstances: 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.