Read the excerpt from a newspaper article about World War I. The gaseous vapor which the Germans used against the French divisions near Ypres last Thursday, contrary to the rules of The Hague Convention, introduces a new element into warfare. The attack of last Thursday evening was preceded by the rising of a cloud of vapor, greenish gray and iridescent. That vapor settled to the ground like a swamp mist and drifted toward the French trenches on a brisk wind. What does the article reveal about the use of chemical weapons?