But sweet vicissitudes of rest and toil
  Make easy labor and renew the soil
  Yet sprinkle sordid ashes all around
  And load with fatt’ning dung thy fallow soil.

The ashes supplied the potash and the dung the nitrate and phosphate.  Long before the discovery of the nitrogen-fixing bacteria, the custom prevailed of sowing pea-like plants every third year and then plowing them under to enrich the soil.  But such local supplies were always inadequate and as soon as deposits of fertilizers were discovered anywhere in the world they were drawn upon.  The richest of these was the Chincha Islands off the coast of Peru, where millions of penguins and pelicans had lived in a most untidy manner for untold centuries.  The guano composed of the excrement of the birds mixed with the remains of dead birds and the fishes they fed upon was piled up to a depth of 120 feet.  From this Isle of Penguins—­which is not that described by Anatole France—­a billion dollars’ worth of guano was taken and the deposit was soon exhausted.

Then the attention of the world was directed to the mainland of Peru and Chile, where similar guano deposits had been accumulated and, not being washed away on account of the lack of rain, had been deposited as sodium nitrate, or “saltpeter.”  These beds were discovered by a German, Taddeo Haenke, in 1809, but it was not until the last quarter of the century that the nitrates came into common use as a fertilizer.  Since then more than 53,000,000 tons have been taken out of these beds and the exportation has risen to a rate of 2,500,000 to 3,000,000 tons a year.  How much longer they will last is a matter of opinion and opinion is largely influenced by whether you have your money invested in Chilean nitrate stock or in one of the new synthetic processes for making nitrates.  The United States Department of Agriculture says the nitrate beds will be exhausted in a few years.  On the other hand the Chilean Inspector General of Nitrate Deposits in his latest official report says that they will last for two hundred years at the present rate and that then there are incalculable areas of low grade deposits, containing less than eleven per cent., to be drawn upon.

Anyhow, the South American beds cannot long supply the world’s need of nitrates and we shall some time be starving unless creative chemistry comes to the rescue.  In 1898 Sir William Crookes—­the discoverer of the “Crookes tubes,” the radiometer and radiant matter—­startled the British Association for the Advancement of Science by declaring that the world was nearing the limit of wheat production and that by 1931 the bread-eaters, the Caucasians, would have to turn to other grains or restrict their population while the rice and millet eaters of Asia would continue to increase.  Sir William was laughed at then as a sensationalist.  He was, but his sensations were apt to prove true and it is already evident that he was too near right for comfort.  Before we were half way to the date he set we had two wheatless days a week, though that was because we persisted in shooting nitrates into the air.  The area producing wheat was by decades:[1]