Notes

Haber played a major role in the development of chemical warfare in World War I, in spite of their proscription in the Hague Convention of 1907 (to which Germany was a signatory). He was promoted to the rank of captain and made head of the Chemistry Section in the Ministry of War soon after the war began.[2]:133 In addition to leading the teams developing chlorine gas and other deadly gases for use in trench warfare, Haber was on hand personally when it was first released by the German military at the Second Battle of Ypres (22 April to 25 May 1915) in Belgium.[2]:138 Haber also helped to develop gas masks with adsorbent filters which could protect against such weapons. A special troop was formed for gas warfare (Pioneer Regiments 35 and 36), under the command of Otto Peterson, with Haber and Friedrich Kerschbaum as advisors. Haber actively recruited physicists, chemists, and other scientists to be transferred to the unit. Future Nobel laureates James Franck, Gustav Hertz, and Otto Hahn served as gas troops in Haber's unit.[2]:136–138 In 1914 and 1915, before the Second Battle of Ypres, Haber's unit investigated reports that the French had deployed Turpenite, a supposed chemical weapon, against German soldiers.[13]

Gas warfare in World War I was, in a sense, the war of the chemists, with Haber pitted against French Nobel laureate chemist Victor Grignard. Regarding war and peace, Haber once said, "During peace time a scientist belongs to the World, but during war time he belongs to his country." This was an example of the ethical dilemmas facing chemists at that time.[14]

Haber was a patriotic German who was proud of his service during World War I, for which he was decorated.[15] He was even given the rank of captain by the Kaiser, rare for a scientist too old to enlist in military service.

In his studies of the effects of poison gas, Haber noted that exposure to a low concentration of a poisonous gas for a long time often had the same effect (death) as exposure to a high concentration for a short time. He formulated a simple mathematical relationship between the gas concentration and the necessary exposure time. This relationship became known as Haber's rule.

Haber defended gas warfare against accusations that it was inhumane, saying that death was death, by whatever means it was inflicted. During the 1920s, scientists working at his institute developed the cyanide gas formulation Zyklon A, which was used as an insecticide, especially as a fumigant in grain stores.[16]