The actual carrying out of the gas operations was intrusted to another professor of chemistry, this being one Haber, of the Kaiser Wilhelm Physical Chemical Institute at Berlin. In 1914, long before the war started, Professor Haber and his assistants are known to have been working secretly with some intensely poisonous arsenic gases and liquids, and one of the assistants was killed and another is reported to have had his arm blown off during the researches. Haber’s particular job was to make all the scientific arrangements in the field; to decide on the gases to be used, and the quantity to employ; to study the wind directions and decide exactly when to make the attack. In the weeks preceding the twenty-second of April, Haber was continually at the Front receiving reports from the wind observation stations and in close touch with the men in charge of the cylinders in the trenches. On several occasions during this time the attack was fixed for a certain hour, but was postponed by Haber, owing to the wind’s being unsuitable. The actual arrangements that had to be made were much more complex than the carrying out of the attack itself. First of all, decision had to be come to as to the gas to be used in the fiendish attempt. Such a gas had of course to be highly poisonous. Then it must be cheaply and easily made in large quantities; it had to be compressible, so that it could be transported easily; it must be heavier than air, so that it should keep close to the ground when first liberated; and for preference it should not be unstable--that is, decompose easily and enter into nonpoisonous combinations with materials, other than man, that it should come across in its passage through the air. Any chemist to whom such a problem is put will inform you there are very few gases that fill the bill. The German choice rested on that gas well-known to students of chemistry--chlorine. Chlorine in large quantities was available from the alkali works in Germany, and it meets all the other requirements except that of not easily combining with other things. This deficiency was fortunate, for it meant that protective chemicals were easy to find when it became necessary to provide respirators to the Allied troops. Then there was the question of transport and emission. The gas was eventually put up in steel cylinders, about thirty inches long and eight inches across and stout enough to stand a pressure of about ten atmospheres, the gas being stored in them compressed to a liquid. On opening such a cylinder the liquid boils and gives off the gas again, but this would not do for field work, because of the intense cold which is produced by the sudden expansion. This would freeze up the pipes and slow down the discharge to such an extent that the gas attack would be too weak.