POISON GAS. In the four years' World War (1914-18), gas was first used in 1915, by the Germans as a means of attack against the French and Canadian troops, who were holding positions on the Ypres salient. • It came as a complete surprise to the Allies who retaliated and later employed poison gas as a weapon, using two methods of attack, commonly known as the gas cloud or mist attack and the gas shell attack. In the gas cloud attack the gases or asphyxiants used are chiefly chlorine and phosgene, which act through the lungs, causing death by suffocation. These gases are heavy, easily turned into liquids and are very poison ous. They are liquified by cold and pressure and placed in metal cylinders, weighing over 100 pounds. The cylinders are taken up to the front line trenches and placed in special em placements under the fire step. When the wind is favorable for an attack the gas is liberated by turning the stop-cock of the cylinders. The gas being heavy, is carried by the wind, close to the ground, towards the troops to be at tacked, remaining in the bottom of the trenches, dugouts, etc., for several days if not removed. In the gas shell attack all areas within five miles of the front line are liable to be attacked. These shells are fired from heavy and light howitzers and trench mortars (Minenwerfer). The greater part of the explosive is removed and replaced by a poisonous liquid, which when the shell bursts, turns into a heavy vapor that hangs about the position for a long time. When fired alone, the shells can be detected by the wobbly motion made coming through the air, by the slight noise made on bursting and by the ap pearance of a whitish cloud when the shell bursts.
Gas shells contain a small bursting charge and a liquid chemical substance which is con vetted into vapor and gas when the shell bursts. To insure satisfactory effects a large number must be discharged in a small space. The bursting charge, though less powerful than that of the ordinary shell, is nevertheless sufficient to produce a considerable explosive effect in addition to the actual gases. Protection of dug outs, cellars, buildings, etc., is given by well fitting doors or by blankets sprayed with hypo solution from a Vermorel sprayer. Practically no gas passes through a wet blanket, and the protection depends on getting a good joint at the sides and bottom of a doorway, so as to stop all draughts. This can be effected by per
mitting the blanket to rest on battens, arranged with a slight slope, against the door frame. The blanket should overlap the outer sides and a fold should lie on the ground at the bottom. The protection afforded by these means is as complete against lachrymatory gases as it is against cloud gas and poisonous shell gases. Chlorine is greenish yellow in color, is two and one-half times heavier than air, and hence rolls along the ground. Phosgene is colorless and is three and one-half times heavier than air. It acts as an asphyxiant, but is only half as strong as chlorine. It has a delayed action on the heart, which acts two days afterward, and hence in trenches after an attack troops and horses are rested for 24 hours, inasmuch as any exertion after being gassed by phosgene makes the effects much worse. It requires from three to six hours to clean away chlorine and phosgene by natural ventilation.
Carbon monoxide, gas shells and mustard gas (q.v.) are most commonly used in gas war fare. Carbon monoxide is not used directly in attacks, but causes many casualties. It attacks the blood corpuscles and they no longer carry oxygen, and being lighter than air it cannot be used as a cloud gas. It cannot be easily liqui fied and hence is not suitable for gas shells. Respirators do not protect against this gas. As a protection from this gas Salvus sets are issued to machine gunners and batteries. These sets consist of cylinders of oxygen opening into bags of waterproof material from which issue tubes leading to mouthpieces and cut off the men entirely from the outside air. Gas shells are ordinary shells from which the greater part of explosive has been taken and replaced by a poisonous liquid, which, when the shell bursts, turns into a poisonous gas or vapor, and being heavy, remains about the place where the shell bursts. Only enough explosive is used to burst the shell and set the gas free. Gas shells are usually divided into four main divisions — as phyxiants, paralysants, lachrymatory and mus tard gas, according to chemicals inside. The mustard gas shell contains heavy liquid which does not evaporate easily and affects the skin, forming ulcers, sores, etc. This gas causes a loss of the sense of smell for other gases tempo rarily.