Reported in Scientific American, This Week in World War I: May 15, 1915
As the Great War ground down to a deadlock, both sides sought some method of gaining an advantage. The Germans (taking a cue from the French) first used poison gas on a wide scale on April 22, 1915, in the trenches near Ypres, Belgium, against French colonial troops. Over 160 tons of chlorine gas were released from almost 6,000 cylinders. The French troops were completely unprotected against gas; they lost over 1,000 men killed, and the rest broke and ran. Luckily for the Allies, the Germans did not expect such a dramatic result and were not prepared to exploit such success.
At this point in the war, the Allies did not know what kind of poison gas they were facing, nor how it was delivered. The cover image [see illustration] is a best-guess interpretation of the technology involved. The cylinders we now know were about five feet tall and weighed about 190 pounds full. The protection that the Germans are shown wearing are the chemical-soaked pads used back then by workers at risk from chlorine gas in industry, and respirator helmets used by fire departments for entering smoke-filled buildings. In reality most of the German troops were apparently as well equipped as their Allied foes: they had no protection at all.
“The reports which have been received seem to show that the gas so far used is chlorine. The greenish yellow color, the strong smell, the great density of the gas causing it to flow along the ground are indications of chlorine. The symptoms shown by its victims are those exhibited by persons who have been poisoned by chlorine in industrial accidents ; that is great irritation of the mucous membranes, bronchitis, and sudden death by a narcotic action in the most severe cases.”
“If chlorine is the gas which was used, it must have reached the trenches in a concentrated form to cause death unless the death was due in part to psychological effects, for to produce death rapidly it is necessary that the air breathed shall contain at least one part of chlorine in 1,000 of air. Long exposure to air containing 1 part of chlorine per 100,000 is dangerous and even smaller amounts are troublesome.”
The Allies started working on countermeasures for chlorine gas immediately.
Ironic note: in the same issue of May 15, 1915, there is an article about the dangers from the lead and sulfuric acid storage batteries aboard U.S. submarines, used for driving electric motors while submerged: “On the United States submarine ‘E-2’ in the autumn of 1914 while at sea on her way from Newport News to New York, the escaping chlorine fumes seriously affected the crew despite prompt measures for their relief.”
Our full archive of the war, called Scientific American Chronicles: World War I, has many articles from 1914–1918 on the chemical aspects of the war. It is available for purchase at www.scientificamerican.com/products/world-war-i/