The final closing of the shell was then effected by motors operated by compressed air. The filled shell were next conveyed to the shell-dump, where they were classified and stored for twenty-four hours, nose down on skids, in order to test them for leaks. The following day the shell were again placed on conveyers which carried them through a painting-machine, where air-brushes gave them a coat of elephant gray and striped them with the distinctive bands of color which denoted the type of gas they contained. The methods followed in filling shell with chlorpicrin were similar to those for phosgene except that refrigeration was unnecessary. The peculiar properties of mustard-gas, however, required an entirely different filling system. Edgewood Arsenal also had separate plants for filling the stannic-chloride hand-grenades used for “mopping up” trenches; for filling both shell and grenades with white phosphorus for use in forming smoke-screens to conceal the movements of advancing troops, and for loading the incendiary drop-bombs used by the Air Service. The various plants which I have just described by no means comprised the whole of Edgewood’s activities, however, for, in order to obtain a sufficient supply of bromine, certain compounds of which are excellent tear-producing materials, a series of brine-wells was sunk at Midland, Michigan; a plant for the production of another lachrymator, brombenzyl cyanide, was erected at Kingsport, Tennessee; and an establishment for the manufacture of diphenychlorarsine—an arsenical material used in gas warfare because it produces violent sneezing, thus causing the troops to remove their gas-masks and thereby exposing them to the effects of the toxic-gases used in combination with the arsenicals—was started at Croyland, Pennsylvania.