Properties
Phosgene is a colorless gas at room temperatures, but becomes a liquid at 8°. The odor of phosgene is suggestive of green corn or musty hay. One liter of phosgene vapor weighs 4.4 grams (chlorine weights 3.22 grams). At 0° C., the liquid is heavier than water, having a specific gravity of 1.432. At 25°, the vapor exerts a pressure of about 25 pounds per square inch. Phosgene is absorbed by solid materials, such as pumice stone and celite. Pumice stone absorbs more than its own weight of phosgene. Thus 5.7 grams of pumice absorbed 7.4 grams phosgene, which completely evaporated in 60 minutes. German shell have been found which contained such a mixture (phosgene and pumice stone). While the apparent reason for their use is to prevent the rapid evaporation of the phosgene, it is a question whether such is the case, for a greater surface is really present in the case of pumice stone than where the phosgene is simply on the ground. Phosgene is slowly decomposed by cold water, rapidly by hot water. This reaction is important because there is always moisture in the air, which would tend to lower the concentration of the gas.
Phosgene is absorbed and decomposed by hexamethylenetetramine (urotropine). This reaction furnished the basis of the first protection used by the British. Later the catalytic decomposition of phosgene into carbon dioxide and hydrochloric acid by the charcoal in the mask furnished protection.
For most purposes a trace of chlorine in phosgene is not a disadvantage; for example, when it is used in cylinders or projectors. Under certain conditions, as when used as a solvent for sneezing gas, the presence of chlorine must be avoided, since it reacts with the substance in solution, usually producing a harmless material. Chlorine may be removed from phosgene by passing the mixture through cotton seed oil.