Chlorine, which is the first gas the Germans used and which is an important constituent of nearly all the other toxic-gases, is derived from ordinary table-salt. It is prepared by passing a current of electricity through a solution of salt, by which process chlorine is liberated and caustic soda formed. At ordinary temperatures chlorine is a greenish-yellow gas of strong, suffocating odor, but by means of cold and pressure it can be readily condensed to a liquid and is usually shipped in that form, stored in strong cylinders. The apparatus in which the salt is decomposed by the electric current is known as a cell. The salt, upon arrival at the arsenal, was taken to the brine building and dumped into large concrete tanks kept partially filled with water, the resulting brine being drawn off, purified, and pumped to the cell-house as needed. The interior of this building was filled with cells, nearly 4,000 in all, through which was passed a direct current of approximately 260 volts. The chlorine thus extracted from the brine was liquefied by compressing it through the agency of a falling column of sulphuric acid and then cooling the compressed gas by refrigeration. Though chlorine has long been manufactured in the United States for chemical purposes, a constant supply of it was so essential for the preparation of the other gases that Colonel Walker insisted that it should be produced at Edgewood, thus making the government independent of private manufacturers. Chlorpicrin, while not so poisonous as some of the other gases, is, nevertheless, an active poison and has, in addition, pronounced lachrymal (tear-producing) and nauseating qualities. Though chlorpicrin is fatal when taken in large quantities, it is almost impossible to inhale much of it because of its terribly nauseating effect. The inhalation of four cubic inches of it causes violent vomiting. Chlorpicrin is produced by the action of picric acid upon chlorine in the form of bleaching-powder. The bleaching-powder, after being diluted with water to the consistency of thick cream, is mixed with a solution of calcium picrate in large stills holding 5,000 or more gallons. A jet of live steam is introduced at the bottom of the still and the reaction begins at once, the resulting chlorpicrin passing out of the still into condensers. This mixture of chlorpicrin and water is then run into tanks. As chlorpicrin does not dissolve in water, it gradually settles to the bottom and is drawn off and loaded directly into the shell.