Chemical warfare

by Amos A. Fries; Clarence J. West

Properties

Chlorine, at ordinary atmospheric pressure and temperature, is a greenish yellow gas (giving rise to its name), which has a very irritating effect upon the membranes of the nose and throat. As mentioned above, at a pressure of 16.5 atmospheres at 18° C., chlorine is condensed to a liquid. If the gas is first cooled to 0°, the pressure required for condensation is decreased to 3.7 atmospheres. This yellow liquid has a boiling point of -33.6° C. at the ordinary pressure. If very strongly cooled, chlorine will form a pale yellow solid (at -102° C.). Chlorine is 2.5 times as heavy as air, one liter weighing 3.22 grams. 215 volumes of chlorine gas will dissolve in 100 volumes of water at 20°. It is very slightly soluble in hot water or in a concentrated solution of salt.

Chlorine is a very reactive substance and is found in combination in a large number of compounds. Among the many reactions which have proved important from the standpoint of chemical warfare, the following may be mentioned:

Chlorine reacts with “hypo” (sodium thiosulfate) with the formation of sodium chloride. Hypo is able to transform a large amount of chlorine, so that it proved a very satisfactory impregnating agent for the early cloth masks.

Water reacts with chlorine under certain conditions to form hypochlorous acid, HOCl. In the presence of ethylene, this forms ethylene chlorhydrin, which was the basis for the first method of preparing mustard gas. In the later method, in which sulfur chloride was used, chlorine was used in the manufacture of the chloride.

Chlorine reacts with carbon monoxide, in the sunlight, or in the presence of a catalyst, to form phosgene, which is one of the most valuable of the toxic gases.

Chlorine and acetone react to form chloroacetone, one of the early lachrymators. The reaction of chlorine with toluene forms benzyl chloride, an intermediate in the preparation of bromobenzylcyanide.

In a similar way, it is found that the greater number of toxic gases use chlorine in one phase or another of their preparation. One author has estimated that 95 per cent of all the gases used may be made directly or indirectly by the use of chlorine.

Chlorine has been used in connection with ammonia and water vapor for the production of smoke clouds. The ammonium chloride cloud thus produced is one of the best for screening purposes. In combination with silicon or titanium as the tetrachloride it has also been used extensively for the same purpose.

On the other hand one may feel that, whatever bad reputation chlorine may have incurred as a poison gas, it has made up for it through the beneficial applications to which it has lent itself. Among these we may mention the sterilization of water and of wounds.

In war, where stationary conditions prevail only in a small number of cases, the use of liquid chlorine for sterilization of water is impractical. To meet this condition, an ampoule filled with chlorine water of medium concentration has been developed, which furnishes a good portable form of chlorine as a sterilizing agent for relatively small quantities of water.

Chlorine has also been applied, in the form of hypochlorite, to the sterilization of infected wounds. The preparation of the solution and the technique of the operation were worked out by Dakin and Carrel. This innovation in war surgery has decreased enormously the percentage of deaths from infected wounds.

CHAPTER VI
PHOSGENE

The first cloud attack, in which pure chlorine was used, was very effective, but only because the troops attacked with it were entirely unprotected. Later, in spite of the varied methods of attack, the results were less and less promising, due to the increased protection of the men and also to the gas discipline which was gradually being developed. During this time the Allies had started their gas attacks (Sept., 1915), and it soon became evident that, if Germany was to keep her supremacy in gas warfare, new gases or new tactics would have to be introduced.

The second poison gas was used in December, 1915, when about 20-25 per cent of phosgene was mixed with the chlorine. Here again the Germans made use of an industry already established. Phosgene is used commercially in the preparation of certain dyestuffs, especially methyl violet, and was manufactured before and during the war by the Bayer Company and the Badische Anilin und Soda Fabrik.

Phosgene can not be used alone in gas cylinders because of its high boiling point (8° C.). While this is considerably below ordinary temperatures, especially during the summer months, the rate of evaporation is so slow that a cloud attack could never be made with it alone. However, when a mixture of 25 per cent phosgene and 75 per cent chlorine, or 50 per cent phosgene and 50 per cent chlorine is used in warm weather there is no difficulty in carrying out gas attacks from cylinders. At the same time the percentage of phosgene in the mixture is sufficiently high to secure the advantages which it possesses. These advantages are at least three:

(a) Phosgene is more toxic than chlorine. It requires 2.5 milligrams per liter of chlorine to kill a dog on an exposure of 30 minutes, but 0.3 milligram of phosgene will have the same effect. This of course means that a cloud of phosgene containing one-eighth (by weight) of the concentration of a chlorine cloud will have the same lethal properties.

(b) Phosgene is much less reactive than chlorine, so that the matter of protection becomes more difficult. Fortunately, word was received by the British of the intended first use of phosgene against them and consequently they were able to add hexamethylenetetramine to the impregnating solution used in the cloth masks.

(c) The third, and a very important, factor in the use of phosgene is the so-called delayed effect. In low concentrations, men may breathe phosgene for some time with apparently no ill effects. Ten or twelve hours later, or perhaps earlier if they attempt any work, the men become casualties.

Pure phosgene has been used in projector attacks ([described in Chapter II]). The substance has also been used in large quantities in shell; the Germans also used shell containing mixtures with superpalite (trichloromethyl chloroformate) or sneezing gas (diphenylchloroarsine).