DICHLOROETHYLSULFIDE
“MUSTARD GAS”
The early idea of gas warfare was that a material, to be of value as a
war gas, should have a relatively high vapor pressure. This would, of
course, provide a concentration sufficiently high to cause casualties
through inhalation of the gas-ladened air. The introduction of
“mustard gas” (dichloroethylsulfide) was probably the greatest single
development of gas warfare, in that it marked a departure from this
early idea, for mustard gas is a liquid boiling at about 220° C., and
having a very low vapor pressure. But mustard gas has, in addition,
a characteristic property which, combined with its high persistency,
makes it the most valuable war gas known at the present time. This
peculiar property is its blistering effect upon the skin. Very low
concentrations of vapor are capable of “burning” the skin and of
producing casualties which require from three weeks to three months for
recovery. The combination of these properties removed the necessity for
a surprise attack, or the building up of a high concentration in the
first few bursts of fire. A few shell, fired over a given area, were
sufficient to produce casualties hours and even days afterwards.
Mustard gas, chemically, is dichloroethylsulfide (ClCH₂CH₂)₂S. The name
originated with the British Tommy because the crude material first
used by the Germans was suggestive of mustard or garlic. Various other
names were given the compound, such as “Yellow Cross,” from the shell
markings of the Germans; “Yperite,” a name used by the French, because
the compound was first used at Ypres; and “blistering gas,” because of
its peculiar effect upon the skin.
HISTORICAL
It seems probable that an impure form of mustard gas was obtained
by Richie (1854) by the action of chlorine upon ethyl sulfide. The
substance was first described by Guthrie (1860), who recognized its
peculiar and powerful physiological effects. It is interesting in this
connection to note that Guthrie studied the effect of ethylene upon
the sulfur chlorides, since this reaction was the basis of the method
finally adopted by the Allies.
The first careful investigation of mustard gas, which was then only
known as dichloroethylsulfide, was carried out by Victor Meyer (1886).
Meyer used the reaction between ethylene chlorhydrin and sodium
sulfide, with the subsequent treatment with hydrochloric acid. All the
German mustard gas used during 1917 and 1918 was apparently made by
the use of these reactions, and all the early experimental work of the
Allies was in this direction.
Mustard gas was first used as an offensive agent by the Germans on
July 12-13, 1917, at Ypres. According to an English report, the
physiological properties of mustard gas had been tested by them during
the summer of 1916. The Anti-Gas Department put forward the suggestion
that it should be used for chemical warfare, but at that time its
adoption was not approved. This fact enabled the English to quickly and
correctly identify the contents of the first Yellow Cross dud received.
It is not true, as reported by the Germans, that the material was first
diagnosed as diethylsulfide.
The tactical value of mustard gas was immediately recognized by the
Germans and they used tremendous quantities of it. During ten days
of the Fall of 1917, it is calculated that over 1,000,000 shell were
fired, containing about 2,500 tons of mustard gas. Zanetti states that
the British gas casualties during the month following the introduction
of mustard gas were almost as numerous as all gas casualties incurred
during the previous years of the war. Pope says that the effects of
mustard gas as a military weapon were indeed so devastating that by the
early autumn of 1917 the technical advisers of the British, French,
and American Governments were occupied upon large scale installations
for the manufacture of this material.
PREPARATION AND MANUFACTURE
The analysis of the first German shell indicated that the mustard gas
contained therein had been prepared by the method published by Victor
Meyer (1886) and later used by Clark (1912) in England. It was natural,
therefore, that attention should be turned to the large scale operation
of this method.
The following operations are involved: Ethylene is prepared by the
dehydration of ethyl alcohol. The interaction of hypochlorous acid
(HClO) and ethylene yields ethylene chlorhydrin, ClCH₂CH₂OH. When
this is treated with sodium sulfide, dihydroxyethyl sulfide forms,
which, heated with hydrochloric acid, yields dichloroethyl sulfide.
Chemically, the reactions may be written as follows:
CH₃CH₂OH = CH₂ : CH₂ + H₂O
CH₂ : CH₂ + HClO = HOCH₂CH₂Cl
2HOCH₂CH₂Cl + Na₂S = (HOCH₂CH₂)₂S + 2NaCl
(HOCH₂CH₂)₂S + 2HCl = (ClCH₂CH₂)₂S + 2H₂O
Without going into the chemistry of this reaction, which is thoroughly
discussed by Gomberg[18] (see also German Manufacture), it may be
said that this “procedure proved to be unsuitable for large scale
production” (Dorsey). As Pope remarks, “That he (the German) should
have been able to produce three hundred tons of mustard gas per month
by the large scale installation of the purely academic method (of
Meyer) constitutes indeed ‘a significant tribute to the potentialities
represented by the large German fine chemical factories.’” It is true
that a great deal of experimental work was carried out by the Allies on
this method, but further study was dropped as soon as the Pope method
was discovered.
[Footnote 18: J. Am. Chem. Soc. =41=, 1414 (1919).]
The first step in advance in the manufacture of mustard gas was the
discovery that ethylene would react with sulfur dichloride. While
American chemists were not very successful in their application of this
reaction, either in the laboratory or the plant, it was apparently,
according to Zanetti, the only method used by the French (the only
one of the Allies that manufactured and fired mustard gas). The plant
was that of the Société Chimique des Usines du Rhone and was started
early in March, 1918, with a production of two to three tons a day.
In July it was producing close to twenty tons a day. The plant was
being duplicated at the time of the Armistice, so that probably in
December, 1918, the production of mustard gas by the dichloride process
would have reached about 40 tons. Zanetti points out, however, that
the process involved complicated and costly apparatus and required
considerable quantities of carbon tetrachloride as a solvent. It is for
this reason that the Levinstein process would have been a tremendous
gain, had the war continued.
About the end of January, 1918, Pope and Gibson, in a study of the
reaction originally used by Guthrie, found that the action of ethylene
upon sulfur chloride (S₂Cl₂) at 60° yielded mustard gas and sulfur:
2CH₂ : CH₂ + S₂Cl₂ = (CH₂ClCH₂)₂S + S
The reaction at this temperature caused the separation of sulfur;
this occurred after the product stood for some time or immediately
if it was treated with moist ammonia gas. While this process was put
into commercial operation, both in England and America, it offered
considerable difficulty from an operating standpoint. The sulfur would
often separate out and block the inlet tubes (ethylene). While it is
comparatively easy to remove the mustard gas from the separated sulfur
by decantation, a certain amount always remains with the sulfur. It is
almost impossible to economically remove this, and its presence adds
to the difficulty of removing the sulfur from the reactors; the men
engaged in this operation almost always become casualties.
[Illustration: FIG. 29.—The Levinstein Reactor as Installed at Edgewood
Arsenal.]
It was especially important, therefore, when Green discovered that, if
the reaction was carried out at 30°, the sulfur did not settle out but
remained in “pseudo solution” in the mustard gas (Pope) or as a loose
chemical combination of the monosulfide (mustard gas) with an atom of
sulfur (Green). This material has all the physiological activity of the
pure monosulfide, while the enormous technical difficulties of handling
separated sulfur are entirely obviated by this method of manufacture.
To carry out the reaction Levinstein, Ltd., devised the Levinstein
“reactor.” The apparatus is shown in Fig. 29. The process consists
essentially in bringing together sulfur chloride and very pure ethylene
gas in the presence of crude mustard gas as a solvent at a temperature
ranging between 30-35° C. A supply of unchanged monochloride is
constantly maintained in the reacting liquid until a sufficiently large
batch is built up. Then the sulfur monochloride feed is discontinued
and the ethylene feed continued until further absorption ceases. By
controlling the ratio of mustard gas to uncombined monochloride, the
reaction velocity is so increased that the lower temperature may be
used.
The product thus obtained is a pale yellow liquid which deposits no
sulfur and requires no further treatment. It is ready for the shell
filling plant at once. The obvious advantage of this method led to its
adoption in all American plants started for the manufacture of mustard
gas (Edgewood, Cleveland and Buffalo).
ETHYLENE
It was known from the work of certain French chemists that in the
presence of such a catalyst as kaolin, ethyl alcohol is dehydrated at
an elevated temperature to ethylene. The process as finally developed
by American chemists consisted essentially in introducing mixtures of
alcohol vapor and steam, in the ratio of one to one by weight, into an
8-inch iron tube with a 3-inch core, in contact with clay at 500-600°
C. The use of steam rendered the temperature control more uniform and
thus each unit had a greater capacity of a higher grade product. The
gaseous products were removed through a water-cooled surface condenser.
One unit of this type had a demonstrated capacity of 400 cubic feet per
hour of ethylene, between 92 and 95 per cent pure, while the conversion
efficiency (alcohol to ethylene) was about 85 per cent. The Edgewood
plant consisted of 40 such units. This would have yielded sufficient
ethylene to make 40 tons of mustard gas per 24-hour day.
The English procedure consisted in the use of phosphoric acid, absorbed
onto coke. An American furnace was designed and built which gave 2,000
cubic feet per hour of ethylene, with a purity of 98 to 99 per cent.
This furnace was not used on a large scale, because of the satisfactory
nature of the kaolin furnaces.
[Illustration: FIG. 30.—Experimental Installation for the Production
of Ethylene by Kaolin Procedure. Capacity 400-600 cu. ft. Ethylene per
hr.]
SULFUR CHLORIDE
Since chlorine was prepared at Edgewood, it was logical that some of
this chlorine should be utilized in the preparation of sulfur chloride.
The plant constructed consisted of 30 tanks (78 inches in diameter and
35 feet long), each capable of producing 20,000 pounds of monochloride
per day. The tanks are partially filled with sulfur and chlorine passed
in. The reaction proceeds rapidly with sufficient heat to keep the
sulfur in a molten condition. If the chlorine is passed in too rapidly,
the heat generated may be sufficient to boil off the sulfur chloride
formed. Hence water pipes are provided so that a supply of cold water
may be sprayed upon the tanks, keeping the temperature within the
proper limits.
[Illustration: FIG. 31.—Row of Furnaces for the Preparation of
Ethylene.]
In the manufacture of one ton of mustard gas, about one ton of sulfur
chloride and a little less than half a ton of ethylene (12,640 cubic
feet) are required.
GERMAN METHOD OF MANUFACTURE[19]
[Illustration: FIG. 32.—Preparation of Ethylene at Badische Anilin und
Soda Fabrik. 60 units.]
[Footnote 19: Norris, _J. Ind. Eng. Chem._, =11=, 821 (Sept., 1919).]
“PREPARATION OF ETHYLENE—The gas was
prepared by passing alcohol vapor over aluminum oxide
at a temperature of 380° to 400°. The details of the
construction of one of the furnaces are given in Figs.
32 and 33. The furnaces were very small and sixty units
were needed to furnish the amount of gas required. The
tubes containing the catalyzer were made of copper and
were heated in a bath of molten potassium nitrate. It
was stated that the catalyzer was made according to the
directions of Ipatieff, and that its life was from 10
to 20 days. The gas produced was washed in the usual
form of scrubber. The yield of ethylene was stated to
be about 90 per cent of the theoretical.
[Illustration: FIG. 33.—Ethylene Production at Badische Anilin und Soda
Fabrik. 1 unit.]
[Illustration: FIG. 34.—Chlorhydrin reaction kettle at Badische Anilin
und Soda Fabrik. 16 units.]
“PREPARATION OF ETHYLENE CHLORHYDRIN—The
reaction was carried out in a cylindrical tank resting
on its side. The tank was furnished with a stirrer and
was insulated by means of cork in order to prevent the
transfer of heat from the atmosphere to the inside.
Enough chloride of lime was introduced into the tank to
furnish 500 kg. of available chlorine, together with 5
cu. m. of water. At first, about 20 cu. m. of carbon
dioxide were led into the mixture, next ethylene, and
later carbon dioxide and ethylene simultaneously. The
rate of absorption of ethylene was noted and when
it slackened, more carbon dioxide was added. Fuller
details as to the addition of the two gases were
not given as it was stated that it was a matter of
judgment on the part of the workman who was carrying
out the operation. The reaction should be carried out
at as low a temperature as possible, but it was found
impossible to work below 5° with the apparatus employed
in this factory. The temperature during the reaction
varied between 5° and 10°. In order to maintain this
temperature, the solution was constantly pumped from
the apparatus through a coil which was cooled by brine.
When ethylene was no longer absorbed and there was an
excess of carbon dioxide present, the solution was
tested for hypochlorous acid. The time required for the
introduction of ethylene was between 2 and 3 hrs.
“The contents of the apparatus were passed through a
filter press by means of which the calcium carbonate
was removed. The solution thus obtained contained from
10 to 12 per cent of ethylene chlorhydrin. It was next
distilled with steam and a distillate collected which
contained between 18 and 20 per cent of chlorhydrin.
The yield of chlorhydrin was from 60 to 80 per cent of
that calculated from the ethylene used.
[Illustration: FIG. 35.—Mustard Gas Manufacture at Leverkusen. Layout
for Chlorination of Thiodiglycol.]
“PREPARATION OF DIHYDROXYETHYLSULFIDE—To
prepare the hydroxysulfide, the theoretical quantity
of sodium sulfide, either in the form of the anhydrous
salt or as crystals, was added to the 18 to 20 per cent
solution of chlorhydrin. After the addition of the
sulfide, the mixture was heated to about 90° to 100°.
It was then pumped to an evaporator, and heated until
all the water was driven off. The glycol was next
filtered from the salt which separated, and distilled
in a vacuum. The yield of glycol was about 90 per cent
of the theoretical, calculated from the chlorhydrin.
“PREPARATION OF DICHLORETHYLSULFIDE—The
thiodiglycol was taken from the rail to two large
storage tanks and thence drawn by vacuum direct to
the reaction vessel. Each reaction vessel was placed
in a separate cubicle ventilated both from above and
below and fitted with glass windows for inspection. The
vessels themselves were made of 1¼ in. cast iron and
lined with 10 mm. lead. They were 2.5 m. high and 2.8
m. in diameter. These tanks were jacketed so that they
could be heated by water and steam, and the reaction
was carried out at 50°. The hydrochloric acid coming
from the main pipe was passed through sulfuric acid so
that the rate could be observed, and passed in by means
of 12 glass tubes of about 2 cm. diameter. The rate of
flow was maintained at as high a rate as possible to
procure absorption. The vapors from the reaction were
led from the vessel through a pipe into a collecting
room, and then through a scrubber containing charcoal
and water, through a separator, and then, finally,
into the chimney. These exhaust gases were drawn off
by means of a fan which was also connected with the
lower part of the chamber in which the reaction vessels
were set, so that all the gases had to pass through
the scrubber before going to the chimney. When the
reaction was completed, the oil was removed by means
of a vacuum, induced by a water pump, into a cast iron
washing vessel.
“The hydrochloric acid layer was removed to a stoneware
receiver, also by vacuum. A glass enabled the operator
to avoid drawing oil over with the acid. The pan was
fitted with a thermometer to the interior as well as to
the jacket. For testing the material during reaction,
provision was made for drawing some up by vacuum to
a hydrometer contained in a glass funnel. The final
test at this point read 126° Tw. Another portion could
be drawn up to a test glass and hydrochloric acid
passed through it in full view. A float contained in
a glass outer tube served to show the level of the
liquid in the vessel. The pans in which the operation
is carried on, as well as those employed for washing
and distilling the product, were of a standard pattern
employed in many other operations in the works.
“The washer consisted of a cast iron vessel, lead
lined, and was 2.5 m. in diameter, 2 m. deep, and
fitted with a dome cover and stirring gear. Lead
pipes served for the introduction of sodium carbonate
solution and water. Similar pipes were fitted for
drawing these off by means of a vacuum. A manhole on
the cover, with a flat top, was fitted with light and
sight glasses to which were fitted a small steam coil
for keeping them clear. The washed oil is drawn off
to a distillation still, which is a cast iron vessel
homogeneously lead coated, 1.5 m. in diameter and 2 m.
deep, fitted with a lead heating coil and connected
through a spiral lead condenser and receiver to a
vacuum pump. The water is distilled from the oil at
a pressure of from 62 to 70 mm. absolute pressure.
When dried, the oil is sent by vacuum to a mixing
vessel, similar in most respects to the washing vessel,
in which it is mixed with an appointed quantity
of solvent, which, in this factory, was usually
chlorobenzene but occasionally carbon tetrachloride.
The relative quantities varied with the time of year,
and instructions were sent from Berlin on this point.
Thence the mixture was passed to a storage tank and
into tank-wagons.”
AMERICAN METHOD OF MANUFACTURE
The Chemical Warfare Service investigated carefully the three methods
(German, French, and English) and finally adopted the Levinstein
process. The following discussion is taken from a report originally
made during construction, Sept., 1918.
The Levinstein reactor consisted of a jacketed and lead-lined vessel or
steel tank, 8 feet 5 inches in diameter and 14 feet tall. The reactor
contained 1,400 feet of lead pipe (outside diameter 2⅜ inches), made up
into five coils, giving a total cooling surface of 1,200 square feet.
The finished charge of such a reactor is 12 tons.
Ethylene was introduced through lead injectors, of which there were 16,
each suspended from its own opening in the top and hanging so that the
end of the injector tube was 12 inches from the bottom of the reactor.
The nozzle of the injector was ³/₁₆ inch outside diameter and ethylene
was introduced through it at 40 pounds pressure.
In starting the reaction, enough sulfur chloride was introduced into
the reactor to cover the central nozzles. Ethylene was now introduced,
and as the reaction proceeded sulfur chloride was added in sufficient
quantities to give a high rate of reaction. Brine or cold water was
introduced through the cooling coils and jacket to keep the reacting
temperature at 35° C.
When the charge was completed, the ethylene was turned off so that only
a small amount bubbled through the nozzles and the charge syphoned
off to the settling tank. These were constructed of iron, 8 feet in
diameter and 19 feet tall. They were provided with iron coils by which
the liquid may be cooled down, or the sulfur, which precipitates in the
bottom, melted. The tank was large enough to hold six complete charges
of mustard gas and all the sulfur from these charges was allowed to
accumulate before removal of the sulfur. The supernatant mustard gas
was drawn off from above this sulfur to storage tanks.
Among the factors which influence the reaction are the following:
A temperature of over 60° C. in lead will decompose the product slowly
when sulfur chloride is present.
The presence of iron decomposes the product rapidly at a temperature of
50° C. and probably at a considerably lower temperature.
The purity of the product is dependent upon the time of reaction. There
is always a slow reaction between the mustard gas and sulfur chloride,
and because of this the charge should be completed in 8 hours.
In general the more sulfur that comes out of the solution, the better
is the product. Temperature has a marked effect on the separation of
sulfur. In order to entirely remove the sulfur from the product it was
the custom to increase the temperature at the close of the reaction
from 55° to 70° C. This, however, caused plugging of the lines and the
reactor.
PROPERTIES
Dichloroethylsulfide (mustard gas) is a colorless, oily liquid, which
has a faint mustard odor. The pure material is said to have an odor
very suggestive of that of water cress. While the odor is more or less
characteristic, it is possible to have extremely dangerous amounts of
the gas in a neighborhood without being detected through its odors. It
still seems to be an open question whether mustard gas paralyzes the
sense of smell. One can find opinions on both sides.
Mustard gas boils at 215°-217° C. at atmospheric pressure, so that
it is at once seen to be a very persistent gas. It distills without
decomposition at this temperature but is best purified by vacuum
distillation, or by distillation with steam. A still for the vacuum
distillation of mustard gas has been described by Streeter.[20]
[Footnote 20: _J. Ind. Eng. Chem._, 11, 292 (1919).]
Mustard gas melts, when pure, at 13° to 14° C. (The ordinary summer
temperature is 20°-25° C.). The ordinary product, as obtained from
the “reactor,” melts from 9°-10° C. In order that the product in the
shell might be liquid at all temperatures, winter as well as summer,
the Germans added from 10 to 30 per cent of chlorobenzene, later using
a mixture of chlorobenzene and nitrobenzene and still later pure
nitrobenzene. Carbon tetrachloride has also been used as a means of
lowering the melting point. Many other mixtures, such as chloropicrin,
hydrocyanic acid, bromoacetone, etc., were tested, but were not
used. The effect on the melting point of mustard gas is shown in the
following table:
MELTING POINT OF MUSTARD GAS MIXTURES
---------+--------------+---------------+---------------
Per Cent | Chloropicrin | Chlorobenzene | Carbon
Added | | | Tetrachloride
---------+--------------+---------------+---------------
0 | 13.4° C. | 13.4° C. | 13.4° C.
10 | 9.8 | 8.4 | 9.8
20 | 6.3 | 6.4 | 6.6
30 | 2.6 | -1.0 | 3.1
---------+--------------+---------------+---------------
The mustard gas as finally made by the United States contained about
17 to 18 per cent sulfur in solution. The gas was then put in shell
and fired without the addition of any solvent. In actual practice this
impure product seemed even more powerful in causing casualties than
equal quantities of the pure mustard gas. Accordingly no redistilling
as originally contemplated was actually carried out.
The specific gravity of mustard gas at 20° is 1.2741. The solid
material has a slightly higher value, being 1.338 at 13°. Its vapor
pressure at room temperature is very low; at 20° this value has been
found to be about 0.06 mm. of mercury.
Mustard gas is practically insoluble in water, less than 0.1 per cent
forming a saturated solution. The reports that a 1 per cent solution
could be obtained did not consider the question of hydrolysis. Mustard
gas is freely soluble in all the ordinary organic solvents, such as
ligroin, alcohol, ether, chloroform, acetic acid, chlorobenzene, etc.
In case the solvent is miscible with water, dilution throws out the
product as an oil.
CHEMICAL PROPERTIES
Mustard gas is very slowly decomposed by water, owing to its very
slight solubility. The products are dihydroxyethylsulfide and
hydrochloric acid:
(ClCH₂CH₂)₂S + 2H₂O = (HOCH₂CH₂)₂S + 2HCl
Certain sulfonated oils accelerate the rate of hydrolysis, both by
increasing the rate of solution and the solubility of the mustard gas.
Alkalies also increase the rate of hydrolysis. Oxidizing agents destroy
mustard gas. This reaction was made use of practically in that solid
bleaching powder was early introduced as a means of destroying mustard
gas in the field. (Fig. 9.)
Chlorinating agents (chlorine, sulfur dichloride, etc.) rapidly
transform mustard gas into an inactive (non-blistering) substance.
Sulfur dichloride was a valuable reagent in both laboratory and works
in “cleaning up” mustard gas. This reaction also explains why the
early attempts to prepare mustard gas by the interaction of ethylene
and sulfur dichloride were unsuccessful. Mustard gas is probably
formed, but is almost immediately chlorinated by the excess of sulfur
dichloride. Sulfur chloride on the other hand has no effect on mustard
gas. Chloramine-T and Dichloramine-T (the valuable therapeutic agents
introduced by Dakin and Carrel for treatment of wounds) also react
with mustard gas. For this reason they were advocated as treatment for
mustard gas burns. But as we will see later, they were not altogether
successful.
DETECTION
At first the only method of detecting mustard gas was through the sense
of smell. It was then believed that concentrations which could not be
detected in this way were harmless. Later this proved not to be the
case, and more delicate methods had to be devised. In the laboratory
and in the field these tests were not very satisfactory, because most
of them depended upon the presence of chlorine, and the majority of the
war gases contained chlorine or one of the other halogens. The Lantern
Test depended upon the accumulation of the halogen upon a copper
gauze and the subsequent heating of the gauze in a Bunsen flame. This
test could be made to detect one part of mustard gas in ten million
parts of air. Another field detector devised by the Chemical Warfare
Service consisted in the use of selenious acid. Here again the lack of
specificity is apparent, for while certain halogen compounds did not
give the test, arsine and organic arsenicals gave a positive reaction
and often in a shorter time than mustard gas.
[Illustration: FIG. 36.—Field Detector for Mustard Gas.]
The Germans are said to have had plates covered with a yellow
composition which had the property of turning black in the presence
of mustard gas. These plates were lowered into the bottom of recently
captured trenches and if, after a few minutes, they turned black, the
presence of mustard gas was suspected. It is also stated that the
characteristic yellow paint on the olive of the mustard gas shell
had the same composition, and was useful in detecting leaky shell.
According to a deserter’s statement, however, reliance upon this test
resulted in casualties in several instances.
A white paint has also been reported which turned red in the presence
of mustard gas. This color change was not characteristic, for tests
made by our Army showed that other oils (aniline, turpentine, linseed)
were found to produce the same effect.
The Chemical Warfare Service was able to develop an enamel and an oil
paint which were very sensitive detectors of mustard gas. Both of these
were yellow and became dark red in contact with mustard gas. The change
was practically instantaneous. The enamel consisted of chrome yellow as
pigment mixed with oil scarlet and another dye, and a lacquer vehicle,
which is essentially a solution of nitrocellulose in amyl acetate.
One gallon of this enamel will cover 946,500 sq. cm., or a surface
equivalent to a band 3 cm. wide on 12,500 seven cm. shell.
The paint was composed of a mixture of 50 per cent raw linseed oil
and 50 per cent Japan drier, with the above dye mixture added to
the required consistency. In contact with liquid mustard gas, this
changes to a deep crimson in 4 seconds. Furthermore, in contact with
arsenicals, this paint changes to a color varying from deep purple
to dark green, the color change being almost instantaneous and very
sensitive, even to the vapors of these compounds. Other substances have
no effect upon the paint.
For field work, however, nothing was found equal to the trained nose,
and it is questionable if any of the mechanical means described will be
used in the field.
PHYSIOLOGICAL ACTION
One of the most interesting phases of mustard gas is its peculiar
physiological action. This has been studied extensively, both as
relates to the toxicity and to the skin or blistering effect.
TOXICITY
When one considers the high boiling point of mustard gas, and its
consequent low vapor pressure, he is likely to conclude that such a
substance would be of comparatively little value as a toxic or poison
gas. While it is true that an important part of the military value
of mustard gas has been because of its vesicant properties, the fact
still remains that it is one of our most toxic war gases. The following
comparison with a few of the other gases indicates this:
-----------------+----------------------
| Mg. per Liter
+---------------+------
| Mice | Dogs
-----------------+---------------+------
Mustard gas | 0.2 | 0.05
Phosgene | 0.3 | ···
Hydrocyanic acid | 0.2 | 0.1
Chloropicrin | 1.5 | 0.8
Chlorine | ··· | 3.0
-----------------+---------------+------
When an animal is exposed to the vapors of mustard gas in high
concentration, it subsequently shows a complexity of symptoms, which
may be divided into two classes:
(1) The local effects on the eyes, skin and respiratory tract.
These are well recognized and consist mainly of conjunctivitis and
superficial necrosis of the cornea; hyperemia, œdema and later,
necrosis of the skin, leading to a skin lesion of great chronicity; and
congestion and necrosis of the epithelial lining of the trachea and
bronchi.
(2) The systemic effects due to the absorption of the substance into
the blood stream, and its distribution to the various tissues of the
body.
The most striking observation about the symptoms of mustard gas
poisoning is the latent period which elapses after exposure before any
serious objective or subjective effects are noted. The developments of
the effects are then quite slow, unless very high superlethal doses
have been inhaled.
At first it was a very serious question whether or not the temporary
blindness resulting from mustard gas would not be permanent. Later, as
the depth and seriousness of some of the body burns became well known,
it was a seven-day wonder that no permanent blindness occurred.
The reason seems to be largely a mechanical one. The constant winking
of the eyelids apparently washes the mustard gas off the eyeball
and carries it away so that not enough remains to burn to the depth
necessary to cause permanent blindness.
Due to the very slight concentrations ordinarily encountered in the
field, resulting from a very slow rate of evaporation, the death rate
is very low, probably under 1 per cent among the Americans gassed with
mustard during the war.
If, on the other hand, the gas be widely and very finely dispersed by
a heavy charge of explosive in the shell, the gas is very deadly. In
such cases the injured breathe in minute particles of the liquid and
thus get hundreds of times the amount of gas that would be inhaled as
vapor. This so-called “high explosive mustard gas shell” was a German
development in the very last months of the war. Its effects were great
enough to make it certain that in the future large numbers of these
shell will be used.
The similarity of the symptoms and pathological effects after the
inhalation of large amounts of the vapor and those following an
injection of an olive oil or water solution of mustard gas led Marshall
and his associates to conclude that in high concentrations mustard gas
is absorbed through the lungs. A further bit of evidence consists in
the isolation of the hydrolysis product, dihydroxyethylsulfide, in the
urine of animals poisoned by inhalation of mustard gas. This product
is not toxic and is not responsible for the effects of mustard gas.
Hydrochloric acid, however, does produce very definite effects upon the
animal and may cause death.
From these facts Marshall[21] has proposed the following mechanism of
the action of mustard gas:
[Footnote 21: Marshall, Lynch and Smith, _J. Pharmacal_, =12=, 291-301
(1918).]
“Dichlorethylsulphide is very slightly soluble in water
and very freely soluble in organic solvents, or has
a high lipoid solubility or partition coefficient.
It would, therefore, be expected to penetrate cells
very readily. Its rapid powers of penetration are
practically proven by its effects upon the skin.
Having penetrated within the living cell, it would
undoubtedly hydrolyze. The liberation of free
hydrochloric acid _within the cell_ would produce
serious effects and might account for the actions of
dichlorethylsulphide. To summarize, then, the mechanism
of the action of dichlorethylsulphide appears to be as
follows:
“1. Rapid penetration of the substance into the cell by
virtue of its high lipoid solubility.
2. Hydrolysis by the water within the cell, to form
hydrochloric acid and dihydroxyethylsulphide.
3. The destructive effect of hydrochloric acid upon
some part or mechanism of the cell.
“Although hydrochloric acid does not penetrate cells
readily and is easily neutralized by the buffer action
of the fluids of the body, we might expect by flooding
the body with large quantities of acid to produce
some of the characteristic effects of mustard gas.
Stimulation of the respiratory center is a well known
effect of acid. Convulsions and salivation may be
produced by injection of hydrochloric acid and we have
been able to produce slowing of the heart by rapid
injection of this acid.
“The delayed action of mustard gas might be explained
by the formation of some compound with some constituent
of the blood. However, blood taken from dogs which had
been poisoned with mustard gas and were exhibiting
typical symptoms at the time, injected into normal
dogs produced no effect. Serum treated in vitro with
mustard gas and allowed to stand and then injected into
a dog, produced no effect. The fluid which is formed
in the vesicle and blebs produced by the application
of mustard gas to the skin produces no mustard gas
effects.”
In studying the toxicity of mustard gas for dogs, it was observed that
a concentration of 0.01 mg. per liter could be tolerated indefinitely.
If this value is considered as a threshold value, and subtracted from
the toxicity values for varying periods of time, it is found that there
is a definite relation between the toxic concentration and the time of
exposure. This is expressed by the formula
(C - 0.01)_t_ = K
where C is the concentration observed for a given time _t_. K has the
approximate value of 1.7, where _t_ varies between 7.5 and 480 minutes.
VESICANT ACTION
In addition to its toxicity mustard gas is highly important because
of its peculiar irritating effect upon the skin. Its value is seen
when we realize that one part in 14,000,000 is capable of causing
conjunctivitis of the eye and that one part in 3,000,000 and possibly
one part in 5,000,000 will cause a skin burn in a sensitive person
on prolonged exposure. According to Warthin, the lesions produced by
mustard gas are those of a chemical, not unlike hydrochloric acid, but
of much greater intensity. The pathology of these lesions has been
carefully studied and fully described by Warthin and Weller in their
book on The Pathology of Mustard Gas. Our observations will therefore
be confined to certain striking features of the vesicant action of this
substance.
VARIATION IN SUSCEPTIBILITY OF THE SKIN
Every worker who has worked with mustard gas has noticed that some
individuals are much more susceptible to skin burns from this substance
than are others. Marshall made a study of 1282 men at Edgewood Arsenal,
using a 1 per cent and a 0.01 per cent solution of mustard gas in
paraffin oil. A small drop of these solutions was applied to the skin
of the forearm of the subject and the arm allowed to remain uncovered
for about 10 minutes. The presence or absence of a positive reaction is
indicated by the appearance or absence of erythema 24 hours later. The
results were as follows:
1% 0.01% % of Total
Positive Positive 3.3
Positive Negative 55.3
Negative Negative 41.4
The test made on 84 negroes gave the following results:
1% 0.01% % of Total
Positive Positive 0.0
Positive Negative 15.0
Negative Negative 78.0
Questionable Negative 7.0
“It is seen from the above tables that negroes as a
race, have a much more resistant skin than white men.
No negro of the 84 examined reacted to the 0.1 per cent
solution, and of course none would react to a more
dilute one. About 10 per cent of white men react to
the 0.1 per cent solution, while 2 to 3 per cent react
to the 0.01 per cent solution or are hypersensitive.
About 78 per cent of the negroes fail to react to the 1
per cent solution, while only 20 to 40 per cent of the
white race do not show a reaction.”
[Illustration: FIG. 37.]
The same individual may also show variations in susceptibility and this
has also been studied by Marshall.
“The effect of exercise and sweating was investigated.
A number of individuals were given vapor burns (one
to five minutes exposure) and then exercised until in
a profuse sweat, and then the same exposure to vapors
made. In all cases the burn produced after exercising
was more severe. Sweating produced by having the
subjects place their feet in hot water, produced the
same increase in susceptibility. That the moisture
on the skin produced by sweating is at least partly,
if not entirely, responsible for the increased
susceptibility, was shown in the following way: An
area of the forearm was kept moist for a few minutes
with wet cotton. The sponge was then removed and two
vapor tests made, one over the moist area and one over
normal, dry skin. In all cases the moist burn was the
more severe, in one, producing a blister where the
control did not.
“The skin of different areas of the body is undoubtedly
somewhat different in its susceptibility. All our
tests have been applied to the forearm. The hands
are considerably more resistant than the forearm.
Tests made by the oil method on the forearm, chest,
and back, however, indicate very little difference
in susceptibility of these areas. The skin in the
neighborhood of old burns has been shown to be more
susceptible.
“In general, the same individual does not become more
susceptible to skin burns from continued exposure
to the vapor. The great number of tests which have
been made on the same individual at different times
and under the same conditions, indicate a remarkable
constancy in reaction. A series of men who were tested
at various times during a period of four months,
revealed slight changes from time to time in some of
the men. No man who originally reacted to only the
1 per cent solution ever reacted to the 0.01, and
likewise, no man who originally reacted to the 0.01
ever failed to react to the 0.1 per cent.
“_Susceptibility of skin of animals._ The paraffin
oil test was used on a number of animals and indicated
that differences in susceptibility exist in different
species and in different individuals of the same
species.”
-----------+--------+----------------------------
| | Percentage Positive to
Species | Number +-------+---------+----------
| Tested | 1 Per | 0.1 Per | 0.01 Per
| | Cent | Cent | Cent
-----------+--------+-------+---------+----------
Horse | 1 | 100 | 100 | 100
Dog | 91 | 83 | 35 | 0
Goat | 11 | 55 | 36 | 0
Rat | 10 | 30 | 20 | 0
Mouse | 7 | 70 | 14 | 0
Rabbit | 2 | 100 | 0 | 0
Guinea-pig | 12 | 33 | 0 | 0
Monkey | 9 | 22 | 0 | 0
-----------+--------+-------+---------+----------
The horse appears to be the most sensitive and the monkey and
guinea-pig the most resistant species, while the dog would seem to have
a sensitivity as near man as any of the species studied. No animal
has yet been found which will give a blister from the application of
mustard gas.
Smith, Clowes and Marshall[22] have studied the mechanism of absorption
by the skin. They find that it is quite evident that the mustard gas
is at first rapidly taken up by some element on, or adjacent to, the
surface of the skin and for two to three minutes it may be completely
removed, and for ten to fifteen minutes partially removed by prolonged
washing With an organic solvent, and to a lesser extent with soap and
water.
[Footnote 22: J. Pharmacol., =13=, 1 (1919).]
An interesting phenomenon is observed when the untreated normal skin
of one subject is impressed for five minutes upon an area of skin
of another subject, which has been exposed previously to the vapors
of mustard gas. Under these circumstances both donor and recipient
may develop burns (due to the transposition of the poison from one
skin to another), the intensity of which will vary according to the
circumstances and the respective sensitiveness of the participants. The
degree of transposition is most strikingly observed in the intensity
of the burn on the donor’s arm. If two similar exposures are made on
the arm of a sensitive man, and one of these burns is treated, so to
speak, by contact for five minutes, with the skin of a resistant man,
the treated burn will be markedly less severe than the control, in some
cases being entirely prevented. If, however, the recipient is equally
sensitive to or more sensitive than the donor, the burns on the latter
will exhibit far less difference. Both treatments may be effected at
once, using two recipients, one more, and the other less, resistant
than the donor. In such a case the burn brought into contact with the
more resistant skin will be the less severe.
Similarly, if a sensitive individual impresses his arm alternately
against burns of the same concentration and exposure on a resistant
and sensitive man, the recipient receives a more severe burn from the
sensitive than from the resistant man.
This indicates that the skin of a resistant individual exhibits a
greater affinity or capacity for mustard gas than that of a sensitive
one. There is an actual partition of the gas between the two skins,
with an evident tendency to establish an equilibrium in which the
larger portion of the gas will remain in that skin which possesses the
greater capacity for it.
“A tentative explanation of this phenomenon can be
made as follows. A three phase system is involved—the
air over the skin surface constitutes the outer phase;
some fatty or keratinous elements of the skin, the
central phase; and a cellular portion of the skin the
inner phase. The central phase is rich in lipoids and
poor in water, while the inner phase is rich in water
and poor in lipoids. After exposure to the vapors
of dichloroethylsulphide the central phase is the
absorbing agent and tends to establish equilibrium with
the other two phases. On account of the lipoid nature
of the central phase no damage is produced here because
the compound is not hydrolyzed. On its passage from
the central to the inner phase hydrolysis takes place
within the cell and damage results when a sufficient
concentration of hydrochloric acid is attained. The
outer phase is constantly being freed from vapor by
diffusion and convection currents, so more and more can
evaporate from the central phase. The susceptibility
of an individual depends on the relative power of
the central phase to hold the poison in an inactive
form (not hydrolyzed) and prevent its entry into the
inner phase at a sufficient velocity to result in the
formation of a toxic concentration. We do not attempt
to localize the central or inner phases with any
definite structure of the skin. As mustard is known to
penetrate the sebaceous ducts the fat here might form
one phase and the epithelial lining another.”
TACTICAL USE OF MUSTARD GAS
As before stated, mustard gas, like most other materials used in war,
was discovered in peace. Indeed, Victor Meyer in 1886 worked out fairly
completely its dangerous characteristics. Like phosgene and chlorine
used before it, the materials for its production were available in
considerable quantities through the manufacture of components either
for dyes or photographic chemicals.
Mustard gas, besides being highly poisonous, has so many other
important qualities as to have given it the designation during the
war of the “king of gases.” That broad distinction it still holds.
Its introduction at Ypres, on the night of July 12, 1917, changed
completely the whole aspect of gas warfare and to a considerable extent
the whole aspect of warfare of every kind. It is highly poisonous,
being in that respect one of the most useful of all war gases. It
produces no immediate discomfort. It has a considerable delay action.
It burns the body inside or out, wherever there is moisture. Eyes,
lungs and soft parts of the body are readily attacked. It lingers for
two or three days in the warmest weather, while in cold, damp weather
it is dangerous for a week or ten days, and in still colder weather
may be dangerous for a month or longer whenever the weather warms up
sufficient to volatilize the liquid. It is only slowly destroyed in the
earth, making digging around shell holes dangerous for weeks and months
and in some cases possibly a year or more.
The Germans first used it simply to get casualties and interfere with
or break up the threatened heavy attacks by the British on the Ypres
salient. While not stopping the inauguration of these attacks in the
fall of 1917, the German use of mustard gas was so effective as to
delay the beginning of those attacks for at least two weeks and thus
gain valuable time for the Germans, besides causing serious casualties
with consequent partial break up of companies, regiments and divisions
in the English Army.
The German used his mustard gas throughout the fall of 1917 and the
winter of 1917 and 1918, as above stated, to produce casualties, to
destroy morale, to break up units, and to interfere with operations
generally. During that time, however, he developed a more scientific
use and when he started his big offensives in March, April, May and
June, 1918, he used mustard gas _before_ the battles to cause losses,
break up units and destroy morale, and also during the progress of
battles to completely neutralize strong points which he felt he did
not want to attempt to take by direct assault. Perhaps the most noted
case of this was at Armentières in April, when he deluged the city to
such an extent that mustard gas is said to have actually run in the
streets. So effective was this gassing that not only did the British
have to withdraw from the city but the Germans could not enter it for
more than two weeks. It, however, enabled the Germans to take the city
with practically no loss of life. There were numerous other cases on a
smaller scale where mustard gas was used in the same way.
On account of its persistence it has been generally referred to as
a defensive gas and for that purpose it is incomparable. The use of
sufficient quantities of mustard gas will almost certainly stop the
occupation of areas by the enemy and probably even stop his crossing
them. It also enables strong points which it is not desired to attack
to be completely neutralized,—that is, made so unhabitable that the
area must be evacuated.
A use that was proposed toward the end of the war, and that will
undoubtedly be made of the gas in the future, is to have it planted
in drums in the ground and exploded when an enemy is attempting to
advance. This would be a highly economic way to distribute great
quantities of the material at the moment and in the place most heeded.
It has even been proposed, and this would seem entirely feasible, to
sprinkle certain of these areas with mustard gas by means of sprinklers
attached to drums or even tanks mounted on trucks.
Just before the Armistice the German made another development in the
use of mustard gas. Instead of the ordinary amount of explosive, which
only fairly opened up the shell and allowed the liquid to escape, he
filled nearly 30 per cent of the total space of the shell with high
explosive. This completely broke up the shell and distributed the
greater part of the liquid mustard gas in the form of a fine spray.
This spray, when breathed, proved extremely deadly, as might be
expected from the fact that when in the form of minute particles one
can draw into the lungs in a single breath one hundred times or more
the amount that he would get of pure gas.
Since mustard gas has such a delay action and is effective in such
small concentrations it can be used very effectively in small calibre
guns, as the 75 mm. or 3-inch. Furthermore, since it lasts for two
or three days at the very least, a small number of guns can keep a
very large area neutralized with the gas. With phosgene and similar
non-persistent gases that volatilize almost completely upon the
burst of the shell it is necessary to build up a high concentration
immediately. The exact opposite is true of mustard gas. Mustard gas
can be fired very slowly with the certain knowledge that all shells
fired at one moment will be effective when the next is fired, though
twelve hours or more may intervene between the first and last firing.
Thus, while with phosgene a large number of guns are needed for a gas
attack, with mustard gas the number can be reduced to one-tenth or even
less. Mustard gas may be in the future and has been in the past used
safely in hand grenades because of its very low vapor tension, whereby
the pressure at ordinary temperatures is exceedingly low. This has
an important bearing on cylinders and other containers for shipping
mustard gas, that is, they need be only strong enough to be safe
against handling and not to withstand the high pressure encountered
with phosgene or chlorine cylinders.
In the future, mustard gas will be used in all the ways above stated
and undoubtedly in many more. It can be fired in large quantities upon
strong points to force their evacuation. It can be fired on the flank
of attacking armies for protection against counter-attacks. It can be
fired against the enemy artillery at all times to silence them and stop
their firing. It was thus used by the Americans in the Argonne against
the enemy on the east bank of the Meuse River, this river separating
the American and German armies. It was extremely effective in stopping
the enemy’s artillery. The high explosive mustard gas shell, not only
because of its persistency but because of its quick deadliness, can be
fired singly and be depended upon to do its work wherever there be men
or animals. One of the greatest uses will be by simple sprinkling from
aeroplanes.
The future will see mustard gas used at nearly all times with a
certain quantity of a powerful lachrymator or tear gas. This is for
the reasons, as stated in the beginning, that mustard gas causes no
immediate discomfort and has no objectionable smell. Accordingly,
if the battle be critical, men may continue to fight from four to
eight hours in a mustard gas atmosphere without masks. It is true the
casualties will be high with a high death rate. Nevertheless, this
period of time might enable the artillery to do such effective work as
to completely stop an attack. If, however, at the instant mustard gas
firing is begun a number of powerful lachrymatory shells are sent over,
the immediate wearing of the mask is forced. The enemy is then subject
to all the burning effects of mustard gas as well as the discomfort of
long wearing of the mask.
It may confidently be expected that further developments in the use of
mustard gas will be made, as well as further developments in methods of
throwing it upon the enemy or of bursting shell containing it in his
midst.