In Search of a Son

by William S. Walsh

"You have never seen oxygen any more than you have seen air," continued Monsieur Roger. "You have never seen it, and you never will see it with your eyes,—for those organs are very imperfect. I need not therefore say oxygen is a colorless gas; and yet I will say it to you by force of habit. All books of chemistry begin in this way. Besides this, it is without smell and without taste. Oxygen is extremely well fitted for combustion. A half-extinguished candle—that is, one whose wick is still burning but without flame—will relight instantly if placed in a globe full of oxygen. Almost all the metals, except the precious metals, such as gold, silver, and platinum, burn, or oxydize more or less rapidly, when they are put in contact with oxygen; for, besides those lively combustions, in which metals, or other materials, become hot and are maintained in a state of incandescence, there are other kinds of burning which may be called slow combustions. You have often had under your eyes, without knowing it, examples of these slow combustions. For example, you have seen bits of iron left in the air, or in the water, and covered with a dark-red or light-red matter."

"That is rust," said Miette.

"Yes, that is what they call rust; and this rust is nothing less than the product of the combustion of the iron. The oxygen which is found in the air, or the water, has come in contact with the bit of iron and has made it burn. It is a slow combustion, without flames, but it nevertheless releases some heat. Verdigris, in some of its forms, is nothing less than the product of the combustion——"

"Of copper," interrupted Miette again.

"Miette has said it. These metals burn when they come in contact with the oxygen of the air,—or, in the language of science, they are oxydized; and this oxydation is simple combustion. Therefore, oxygen is the principal agent in combustion. The process which we call burning is due to the oxygen uniting itself to some combustible body. There is no doubt on that subject, for it has been found that the weight of the products of combustion is equal to the sum of the weight of the body which burns and that of the oxygen which combines with it. In the experiment which we have made, if the oxygen has diminished in the globe, if it seems to have disappeared, it is because it has united itself and combined with the carbon of the candle to form the flame. In the same way in Lavoisier's experiment it had combined itself with the mercury to form the red pellicles. The candle had gone out when all the oxygen in the globe had been absorbed; the red pellicles had ceased to form when they found no more oxygen. In this way Lavoisier discovered that the air was formed of a mixture of two gases: the first was oxygen, of which we have just spoken; the second was nitrogen. The nitrogen, which is also a colorless, odorless, and tasteless gas, possesses some qualities that are precisely contrary to those of oxygen. Oxygen is the agent of combustion. Nitrogen extinguishes bodies in combustion. Oxygen is a gas indispensable to our existence, with which our lungs breathe, and which revives our being. The nitrogen, on the contrary, contains no properties that are directly useful to the body. Animals placed in a globe full of nitrogen perish of asphyxia. In other words, they drown in the gas, or are smothered by it. I suppose you will ask me what is the use of this gas, and why it enters into the composition of the air? You will ask it with all the more curiosity when you know that the air contains four times as much nitrogen as oxygen; to be exact, a hundred cubic feet of air contains seventy-nine cubic feet of nitrogen and twenty-one cubic feet of oxygen. Now, the important part that nitrogen plays is to moderate the action of the oxygen in respiration. You may compare this nitrogen mixed with oxygen to the water which you put in a glass of wine to temper it. Nitrogen possesses also another property which is more general: it is one of the essential elements in a certain number of mineral and vegetable substances and the larger portion of animal substances. There are certain compounds containing nitrogen which are indispensable to our food. An animal nourished entirely on food which is destitute of nitrogen would become weak and would soon die."

"Excuse me, Monsieur Roger," said Albert Dalize: "how can nitrogen enter into our food?"

"That is a very good question," added Miette, laughing; "surely you cannot eat nitrogen and you cannot eat gas."

"The question is indeed a very sensible one," answered Monsieur Roger; "but this is how nitrogen enters into our food. We are carnivorous, are we not? we eat meat and flesh of animals. And what flesh do we chiefly eat? The flesh of sheep and of cattle. Sheep and cattle are herbivorous: they feed on herbs, on vegetables. Now, vegetables contain nitrogen. They have taken this nitrogen, either directly or indirectly, from the atmosphere and have fixed it in their tissues. Herbivorous animals, in eating vegetables, eat nitrogen, and we, who are carnivorous, we also eat nitrogen, since we eat the herbivorous animals. We also eat vegetable food, many kinds of which contain more or less nitrogen. Do you understand?"

"Yes, I understand," said Miette.