During a press conference at Camp David, President Obama said that chlorine isn’t ‘historically’ a chemical weapon.

“Now there’s a possibility that Assad has once again used chemical weapons,” reporter Mike Viquera said. “What did you tell these leaders here, who are disappointed last time, and will you use a military response if it’s confirmed that he used chemical weapons again?”

President Obama said that “Assad gave up his chemical weapons. And that’s not speculation on our part. That, in fact, has been confirmed by the organization internationally, that is charged with eliminating chemical weapons.”

“We have seen reports about the use of chlorine in bombs that had the effect of chemical weapons. Chlorine, chlorine, itself, historically has not been listed as a chemical weapon, but when it is used in this fashion, can be considered a prohibited use of that particular chemical,” President Obama said.

About three weeks later, German troops used chlorine gas for the first time on a mass scale during combat on the Western Front near the Flemish city of Ypres in Belgium, deploying a total of 150 tons of the substance. At first, French soldiers thought the shimmering cloud was intended as a diversionary tactic. But then, suddenly, they began flailing about with their hands in the air as they gasped for breath and collapsed on the ground. As many as 1,200 were killed and 3,000 wounded. Haber observed the event from a safe distance.