(2a) Chlorine is very readily manufactured by the electrolysis of a salt (sodium chloride) solution. The operation is described below. In 100-pound cylinders, the commercial product sold before the War for 5 cents a pound. Therefore on a large scale, it can be manufactured at a very much smaller figure.
(3a) Chlorine is easily liquefied at the ordinary temperature by compression, a pressure of 16.5 atmospheres being required at 18° C. The liquid which is formed boils at -33.6° C. at ordinary atmospheric pressure, so that it readily vaporizes upon opening the valve of the containing cylinder. Such rapid evaporation inside would cause a considerable cooling of the cylinder, but this is overcome by running the outlet pipe to the bottom of the tank, so that evaporation takes place at the end of the outlet pipe.
(4a) Chlorine is 2.5 times as heavy as air, and therefore the gas is capable of traveling over a considerable distance before it dissipates into the atmosphere.
(5a) The only point in which chlorine does not seem to be an ideal gas, is in the fact that it is a reactive substance. This is best seen in the success of the primitive protection adopted by both the British and the French during the days immediately following the first gas attack.
At first, however, chlorine proved a very effective weapon. During the first six months of its use, its value was maintained by devising new methods of attack. When these were exhausted, phosgene was added ([see next chapter]). With the decline in importance of cloud gas attacks, and the development of more deadly gases, chlorine was all but discarded as a true war gas, but remained as a highly important ingredient in the manufacture of other toxic gases.
Manufacture in the United States
It was at first thought that the existing plants might be able to supply the government’s need of chlorine. The pre-war production averaged about 450 tons (900,000 pounds) per day. The greater amount of this was used in the preparation of bleach, only about 60,000 pounds per day being liquefied. Only a few of the plants were capable of even limited expansion. In an attempt to conserve the supply, the paper mills agreed to use only half as much bleach during the war, which arrangement added considerably to the supply available for war purposes. It was soon recognized that even with these accessions, large additions would have to be made to the chlorine output of the country in order to meet the proposed toxic gas requirements.
After a careful consideration of all the factors, the most important of which was the question of electrical energy, it was decided to build a chlorine plant at Edgewood Arsenal, with a capacity of 100 tons (200,000 pounds) per day. The Nelson cell was selected for use in the proposed plant. During the process of erection of the plant, the Warner-Klipstein Chemical Company, which was operating the Nelson cell in its plant in Charleston, West Virginia, agreed that men might be sent to their plant to acquire the special knowledge required for operating such a plant. Thus when the plant was ready for operation, trained men were at once available.
Fig. 19.—Chlorine Plant, Edgewood Arsenal.