advance by working out methods of getting nitrogen from the air.  Long ago it was said that the British ruled the sea and the French the land so that left nothing to the German but the air.  The Germans seem to have taken this jibe seriously and to have set themselves to make the most of the aerial realm in order to challenge the British and French in the fields they had appropriated.  They had succeeded so far that the Kaiser when he declared war might well have considered himself the Prince of the Power of the Air.  He had a fleet of Zeppelins and he had means for the fixation of nitrogen such as no other nation possessed.  The Zeppelins burst like wind bags, but the nitrogen plants worked and made Germany independent of Chile not only during the war, but in the time of peace.

Germany during the war used 200,000 tons of nitric acid a year in explosives, yet her supply of nitrogen is exhaustless.

[Illustration:  World production and consumption of fixed inorganic nitrogen expressed in tons nitrogen

From The Journal of Industrial and Engineering Chemistry, March, 1919.]

Nitrogen is free as air.  That is the trouble; it is too free.  It is fixed nitrogen that we want and that we are willing to pay for; nitrogen in combination with some other elements in the form of food or fertilizer so we can make use of it as we set it free.  Fixed nitrogen in its cheapest form, Chile saltpeter, rose to $250 during the war.  Free nitrogen costs nothing and is good for nothing.  If a land-owner has a right to an expanding pyramid of air above him to the limits of the atmosphere—­as, I believe, the courts have decided in the eaves-dropping cases—­then for every square foot of his ground he owns as much nitrogen as he could buy for $2500.  The air is four-fifths free nitrogen and if we could absorb it in our lungs as we do the oxygen of the other fifth a few minutes breathing would give us a full meal.  But we let this free nitrogen all out again through our noses and then go and pay 35 cents a pound for steak or 60 cents a dozen for eggs in order to get enough combined nitrogen to live on.  Though man is immersed in an ocean of nitrogen, yet he cannot make use of it.  He is like Coleridge’s “Ancient Mariner” with “water, water, everywhere, nor any drop to drink.”

Nitrogen is, as Hood said not so truly about gold, “hard to get and hard to hold.”  The bacteria that form the nodules on the roots of peas and beans have the power that man has not of utilizing free nitrogen.  Instead of this quiet inconspicuous process man has to call upon the lightning when he wants to fix nitrogen.  The air contains the oxygen and nitrogen which it is desired to combine to form nitrates but the atoms are paired, like to like.  Passing an electric spark through the air breaks up some of these pairs and in the confusion of the shock the lonely atoms seize on their nearest neighbor and so may get partners of the other sort.  I have seen this same thing happen in a square dance where somebody made a blunder.  It is easy to understand the reaction if we represent the atoms of oxygen and nitrogen by the initials of their names in this fashion: