girls working with
cordite get to using it as chewing gum; a harmful habit, not because of
any danger of being blown up by it, but because nitroglycerin is a heart
stimulant and they do not need that.

[Illustration: The Genealogical Tree of Nitric Acid From W.Q. Whitman's
"The Story of Nitrates in the War," _General Science Quarterly_]

TNT is by no means smokeless. The German shells that exploded with a
cloud of black smoke and which British soldiers called "Black Marias,"
"coal-boxes" or "Jack Johnsons" were loaded with it. But it is an
advantage to have a shell show where it strikes, although a disadvantage
to have it show where it starts.

It is these high explosives that have revolutionized warfare. As soon as
the first German shell packed with these new nitrates burst inside the
Gruson cupola at Liege and tore out its steel and concrete by the roots
the world knew that the day of the fixed fortress was gone. The armies
deserted their expensively prepared fortifications and took to the
trenches. The British troops in France found their weapons futile and
sent across the Channel the cry of "Send us high explosives or we
perish!" The home Government was slow to heed the appeal, but no
progress was made against the Germans until the Allies had the means to
blast them out of their entrenchments by shells loaded with five hundred
pounds of TNT.

All these explosives are made from nitric acid and this used to be made
from nitrates such as potassium nitrate or saltpeter. But nitrates are
rarely found in large quantities. Napoleon and Lee had a hard time to
scrape up enough saltpeter from the compost heaps, cellars and caves for
their gunpowder, and they did not use as much nitrogen in a whole
campaign as was freed in a few days' cannonading on the Somme. Now there
is one place in the world--and so far as we know one only--where
nitrates are to be found abundantly. This is in a desert on the western
slope of the Andes where ancient guano deposits have decomposed and
there was not enough rain to wash away their salts. Here is a bed two
miles wide, two hundred miles long and five feet deep yielding some
twenty to fifty per cent. of sodium nitrate. The deposit originally
belonged to Peru, but Chile fought her for it and got it in 1881. Here
all countries came to get their nitrates for agriculture and powder
making. Germany was the largest customer and imported 750,000 tons of
Chilean nitrate in 1913, besides using 100,00