Science in the Service of Man
In the minds of many, the importance of air is confined to its being necessary to life because it is essential for breathing. But when we confine our concern to this important side of it, we are in truth thinking of the oxygen gas present in the air, forgetting another gas of the greatest importance: azote, or nitrogen, which makes up more than 75 percent of the weight of the air, whereas oxygen makes up only about 23 percent of that weight. The remaining two percent consists of
the rare gases, such as argon, neon, hydrogen, and carbonic gas.
Nitrogen in itself is a chemical element of little and sluggish activity, and in the air it tempers the sharpness of oxygen; for pure, unmixed oxygen is a gas that bears very harshly upon the tissues of the lungs. But nitrogen is of very great importance when it enters, with other elements, into chemical reactions from which result compounds indispensable to animal and plant alike. The proteins of which all the cells in the body of animal and plant are composed are organic compounds whose existence would be impossible did they not contain the element nitrogen. Nitrogen compounds, then, are of fundamental importance in our organic life, and it is fortunate indeed that the air we breathe is an inexhaustible well of this important element.
In this article I shall try to explain how this gas of little activity is transformed into useful compounds.
1 — The Nitrogen-Fixing Bacteria
By the phrase "fixing nitrogen" I mean converting the gas into stable chemical compounds fit for use.
In the earth there exists a kind of bacteria possessed of this wonderful power of taking nitrogen from the air and making it react — in an obscure fashion which we do
not exactly understand — with the elements present in the soil, such as potassium and oxygen; and from this reaction results the compound known as nitrate of potash (Nitrate de Potasse), a compound the plant uses for its nourishment. These bacteria are found on the roots of green vegetable plants such as beans, peas, and broad beans. When these bacteria perform their function, the plant's roots absorb these nourishing chemical compounds necessary for their growth. Therefore, when we eat these vegetables, or meat (which comes from animals that eat plants and feed upon them), we should remember that the primary source of our food in this case is the nitrogen present in the air.
That is the work of nature. Let us look now at the work of man.
2 — Artificial Nitrogen Compounds
Science makes an effective contribution in the field of agriculture, for it enables us to prepare the
chemical fertilizers that set this important side of agriculture upon a sound scientific and experimental basis. Among the most important chemical fertilizers are the nitrates, that is, compounds of nitrogen with oxygen and with other elements such as sodium, potassium, and calcium. The sole source of these important compounds used to be the state of Chile in South America. But modern chemistry has been able to do without Chilean nitrate by converting the nitrogen of the air into nitrates, as follows:
A suitable quantity of hydrogen gas is taken and burned in a large chamber containing air. The result of this combustion is that the hydrogen unites with the oxygen of the air and the two compose water (for water is composed of the two elements hydrogen and oxygen). In this way the oxygen is set apart and the nitrogen alone remains. This gas is then mixed with a further quantity of hydrogen, in the proportion of one part nitrogen to three parts hydrogen. The mixture is then placed in strong steel cylinders in which the temperature rises to about 475 degrees centigrade and the pressure is about a ton and a half to the square centimeter — that is, 1,500 times greater than ordinary atmospheric pressure (which amounts to about 1,033 grams to the square centimeter).
The result of this operation is that the two gases unite, and from this union is formed the gas known as ammonia (Ammoniaque).
After this gas has been obtained, a second operation is carried out upon it: this time it is mixed with air, and the whole is driven through a fine, red-hot screen of platinum, whereupon the oxygen of the air unites with the ammonia and a new gas is formed which, when dissolved in water, gives the acid known as nitric or azotic acid (Acide Nitrique ou Azotique).
And this nitric acid is the