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).
MANUFACTURE
Phosgene was first prepared by John Davy in 1812, by exposing a
mixture of equal volumes of carbon monoxide and chlorine to sunlight;
Davy coined the name “phosgene” from the part played by light in the
reaction. While phosgene may be prepared in the laboratory by a number
of other reactions, it was quite apparent that the first mentioned
reaction is the most economical of these for large scale production.
The reaction is a delicate one, however, and its application required
extended investigation.
The United States was fortunate in that, for some months previous to
the war, the Oldbury Electrochemical Company had been working on the
utilization of their waste carbon monoxide in making phosgene. The
results of these investigations were given to the government and aided
considerably in the early work on phosgene at the Edgewood plant.
[Illustration: FIG. 23.—Furnace for Generating Carbon Monoxide.]
Of the raw materials necessary for the manufacture of phosgene, the
chlorine was provided, at first by purchase from private plants, but
later through the Edgewood chlorine plant. After a sufficient supply of
chlorine was assured the next question was how to obtain an adequate
supply of carbon monoxide. A method for this gas had not been developed
on a large scale because it had never been necessary to make any
considerable quantity of it. The French and English passed oxygen up
through a gas producer filled with coke; the oxygen combines with the
carbon, giving carbon monoxide. The oxygen was obtained from liquid
air, for which a Claude liquid air machine may be used. The difficulty
with this method of preparing carbon monoxide was that the amount of
heat generated was so great that the life of the generators was short.
Our engineers conceived the idea of using a mixture of carbon dioxide
and oxygen. The union of carbon dioxide with carbon to form carbon
monoxide is a reaction in which heat is absorbed. Therefore by using
the mixture of the two gases, the heat of the one reaction was absorbed
by the second reaction. In this way a very definite temperature could
be maintained, and the production of carbon monoxide was greatly
increased.
[Illustration: FIG. 24.—Catalyzer Boxes Used in the Manufacture of
Phosgene.]
Carbon dioxide was prepared by the combustion of coke. The gas was
washed and then passed into a solution of potassium carbonate. Upon
heating, this evolved carbon dioxide.
Phosgene was then prepared by passing the mixture of carbon monoxide
and chlorine into catalyzer boxes (8 feet long, 2 feet 9 inches deep
and 11 inches wide), which are made of iron, lined with graphite and
filled with a porous form of carbon. Two sets of these boxes were used.
In the first the reaction proceeds at room temperature, and is about
80 per cent complete. The second set of boxes were kept immersed in
tanks filled with hot water, and there the reaction is completed.
The resulting phosgene was dried with sulfuric acid and then condensed
by passing it through lead pipes surrounded by refrigerated brine.
The Germans prepared their phosgene by means of a prepared charcoal
(wood or animal). Carbon monoxide was manufactured by passing carbon
dioxide over wood charcoal contained in gas-fired muffles and was
washed by passing through sodium hydroxide. This was mixed with
chlorine and the mixture passed downward through a layer of about 20
cm. of prepared charcoal contained in a cast iron vessel 80 cm. in
diameter and 80 cm. deep. By regulating the mixture so that there was
a slight excess of carbon monoxide, the phosgene was obtained with
only one-quarter of one per cent free chlorine. The charcoal (wood)
was prepared by washing with hydrochloric and other acids until free
from soluble ash; it was then washed with water and dried in vacuum.
The size of the granules was about one-quarter inch mesh. Their life
averaged about six months.
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.
PROTECTION
It was mentioned above that hexamethylenetetramine (urotropine) was
used in the early pads (black veil and similar masks) and flannel
helmets. This was found to be satisfactory against chlorine and
phosgene, in the concentrations usually found during a cylinder attack.
The mixture used consisted of urotropine, sodium thiosulfate (“hypo”),
sodium carbonate and glycerine. The glycerine tended to keep the pads
moist, while the other chemicals acted as protective agents against the
mixture of phosgene and chlorine.
The introduction of the Standard Box Respirator with its charcoal-soda
lime filling increased very materially the protection against phosgene.
In this filling, the charcoal both absorbs the phosgene and catalyzes
the reaction with the moisture of the air with which the phosgene is
mixed, to form hydrochloric acid and carbon dioxide. Soda-lime absorbs
phosgene but does not catalyze its decomposition. This shows the
advantage of the mixture, since the hydrochloric acid, which is formed
through the action of the charcoal, is absorbed by the soda-lime.
Experiments seem to indicate that it does not matter which material
is placed in the bottom of the canister, but that an intimate mixture
is the best arrangement. Using a concentration of 5,000 parts per
million (20.2 mg. per liter) a type _H_ canister (see page 217) will
give complete protection for about 40 minutes; when the air-gas mixture
passes at the rate of 16 liters per minute the efficiency or life of a
canister increases with a decrease in temperature, as is seen in the
following table (the concentration was 5,000 parts per million, the
rate of flow 16 liters per minute)
Temperature Efficiency
° C. (Time in minutes)
-10 223
0 172
10 146
20 130
30 125
40 99
From these figures it is seen that at -10° C. the life is about 50 per
cent greater than at summer temperature. As would be expected the life
of a canister is shortened by increasing the concentration of phosgene
in the phosgene air mixture. This is illustrated by the following
figures:
Concentration Life
p.p.m. (Time in minutes)
5,000 177
10,000 112
15,000 72
20,000 58
25,000 25
(25,000 p.p.m. is equal to 101.1 mg. per liter.)
There is rather a definite relation between the concentration of the
gas and the life of a canister at any given rate of flow. Many of these
relations have been expressed by formulas of which the following is
typical. At 32 liters per minute flow, =C⁰˙⁹ × Tb = 101,840=, in which
=C= is the concentration and =T= the time.
SHELL FILLING
The empty shell, after inspection, are loaded on trucks, together with
the appropriate number of “boosters,” which screw into the top of the
shell and thereby close them. The trucks are run by an electric storage
battery locomotive to the filling unit. The shell are transferred by
hand to a conveyor, which carries the shell slowly through a cold room.
During this passage of about 30 minutes, the shell are cooled to about
0° F. The cooled shell are transferred to shell trucks, each truck
carrying 6 shell. These trucks are drawn through the filling tunnel by
means of a chain haul operated by an air motor to the filling machine.
Here the liquid phosgene is run into the shell by automatic machines,
so arranged that the 6 shell are at the same time automatically filled
to a constant void. The truck then carries the filled shell forward a
few feet to a small window, at which point the boosters are inserted
into the nose of the shell by hand. The final closing of the shell is
then effected by motors operated by compressed air. The filling and
closing machines are all operated by workmen on the outside of the
filling tunnel.
[Illustration: FIG. 25.—Filling Livens’ Drums with Phosgene.]
The filled shell are conveyed to the shell dump, where they are stored
for 24 hours, nose down on skids, in order to test for leaks.
TACTICAL USE
Phosgene was first used in cloud attacks in December, 1915. These
attacks continued for about nine months and were then gradually
replaced, to a large extent, by gas shell attacks. Phosgene was
first found in German projectiles in November, 1916. These shell
were known as the D-shell. Besides pure phosgene, mixtures of
phosgene and chloropicrin, phosgene and superpalite, and phosgene and
diphenylchloroarsine have been found.
[Illustration: FIG. 26.—Interior of a Shell Dump.]
The English introduced the use of projectors in the Spring of 1917.
They have a decided advantage over shell in that they hold a larger
volume of gas and readily lend themselves to surprise attacks. As the
Germans say, “the projector combines the advantages of gas clouds and
gas shell. The density is equal to that of gas clouds and the surprise
effect of shell fire is also obtained.”
Toward the close of the war, the Germans made use of a mixture of
phosgene and pumice stone. A captured projector contained about
13 pounds of phosgene and 5½ pounds of pumice. There seems to be
some question as to the value of such a procedure. Lower initial
concentrations are secured; this is due, in part of course, to the
smaller volume of phosgene in the shell containing pumice. Pumice does
seem to keep the booster from scattering the phosgene so high into the
air, and at the same time does not prevent the phosgene from being
liberated in a gaseous condition. This would indicate that pumice gives
a more even and uniform dispersion and a more economical use of the gas
actually used.
Owing to its non-persistent nature (the odor disappears in from one and
a half to two hours) and to its general properties, phosgene really
forms an ideal gas to produce casualties.
ACTION ON MAN
Phosgene acts both as a direct poison and as a strong lung irritant,
causing rapid filling of the lungs with liquid. The majority of deaths
are ascribed to the filling up of the lungs and consequently to the
suffocation of the patients through lack of air. This filling up of
the lungs is greatly hastened by exercise. Accordingly, all rules
for the treatment of patients gassed with phosgene require that they
immediately lie down and remain in that position. They are not even
allowed to walk to a dressing station. The necessity of absolute quiet
for gassed patients undoubtedly partly accounts for the later habit of
carrying out a prolonged bombardment after a heavy phosgene gas attack.
The high explosive causes confusion, forcing the men to move about more
or less and practically prevents the evacuation of the gassed. In the
early days of phosgene the death rate was unduly high because of lack
of knowledge of this action of the gas. Due to the decreased lung area
for oxygenizing the air, a fearful burden is thrown on the heart, and
accordingly, those with a heart at all weak are apt to expire suddenly
when exercising after being gassed.
As an illustration of the delayed action of phosgene, a large scale
raid made by one of the American divisions during its training is
highly illuminating.
This division decided to make a raid on enemy trenches which were
situated on the opposite slope of a hill across a small valley. Up
stream from both of the lines of trenches was a French village in the
hands of the Germans. When the attack was launched the wind was blowing
probably six or seven miles per hour directly down stream from the
village, i.e., directly toward the trenches to be attacked. The usual
high explosive box barrage was put around the trenches it was intended
to capture.
Three hundred Americans made the attack. During the attack a little
more than three tons of liquid phosgene was thrown into the village in
75- and 155-millimeter shells. The nearest edge of the village shelled
with phosgene was less than 700 yards from the nearest attacking
troops. None of the troops noticed the smell of phosgene, although the
fumes from high explosive were so bad that a few of the men adjusted
their respirators. The attack was made about 3 A.M., the men remaining
about 45 minutes in the vicinity of the German trenches. The men then
returned to their billets, some five or six kilometers back of the
line. Soon after arriving there, that is in the neighborhood of 9
A.M., the men began to drop, and it was soon discovered that they were
suffering from gas poisoning. Out of the 300 men making the attack 236
were gassed, four or five of whom died.
The Medical Department was exceedingly prompt and vigorous in the
treatment of these cases, which probably accounted for the very low
mortality.
This is one of the most interesting cases of the delayed action that
may occur in gassing from phosgene. Here the concentration was slight
and there is no doubt its effectiveness was largely due to the severe
exercise taken by the men during and after the gassing.
It should be remarked in closing that while gas officers were not
consulted in the planning of this attack, a general order was shortly
thereafter issued requiring that gas officers be consulted whenever gas
was to be used.