CHAPTER XXI_Chemical warfare

THE PHARMACOLOGY OF WAR GASES

The pharmacology of war gases plays such an important part in chemical

warfare that a brief discussion may well be given of the methods

used in the testing of gases for toxicity and other pharmacological

properties.

War gases may be divided into two groups: persistent and

non-persistent, each of which may include several classes:

I. Lethal

II. Lachrymatory

III. Sternutatory

IV. Special

Each class necessitates special tests in order to determine whether or

not it is suitable for further development.

TOXICITY

One of the first points which must be carefully determined in

investigating a substance is its toxicity. It is important that this be

determined for numerous reasons:

1. To determine what concentrations are dangerous in the field.

2. To ascertain how effective protective devices have to be to furnish

sufficient protection against the gas.

3. To furnish a basis for accurate experimental work on the treatment

of gassed cases.

4. To decide whether or not the material is worthy of further

development in the laboratory or in the plant.

These considerations necessitate the determination of the toxicity in

the form of a vapor and not by the ordinary method of administration

by mouth, through the skin (subcutaneously) or through the blood

(intravenously). The simplest method of determining the toxicity of

a substance as a vapor would be to place animals in a gas-tight box

and introduce a known amount of the substance in the form of vapor.

But by this method the concentration is not accurately known unless

chemical analyses of the air are made, and then it is found to be much

less than that calculated from the amount of substance introduced,

because of condensation on the walls of the chamber, or absorption of

the substance by the skin and hair of the animal and in some cases, of

decomposition of the substance by moisture in the air. Moreover, it is

found that the concentration decreases markedly with time. Because of

these factors, the figures used for the concentration are more or less

guess work. To overcome these difficulties, a chamber is used through

which a continuous current of air, containing a known and constant

amount of the poisonous vapor, is passed. Such an apparatus is shown in

Fig. 116.

[Illustration: FIG. 116.—Continuous Flow Gassing Chamber for Animals.]

The flask _E_ is a 300 cc. Erlenmeyer flask, with a ground glass

stopper. The liquid to be tested is placed in this flask together

with a sufficient quantity of glass wool to prevent splashing and the

carrying over mechanically of droplets of the liquid. Air is passed

through _A_ and _C_ (calcium chloride drying tubes) and the rate

measured by the flow meter _D_. The air and gas are mixed in _F_ before

passing into the chamber _G_. This chamber is made of plate glass, is

of about 100 liters capacity, and is air-tight. The entire flow of air

and gas through the box, kept constant at 250 liters per minute, is

measured at _H_. The gas is removed through _K_, which is filled with

charcoal and soda-lime, in order that little gas may pass into the pump.

By weighing the flask _E_, and its contents before and after passing

air through it, and knowing the total volume of the mixture passing

through the chamber during the same period, the concentration of the

substance can readily be calculated. This concentration, as determined

by the “loss in weight” method, can be checked by chemical analysis

(samples taken at _M_—_M_). The method has been found to give accurate

values.

The concentration in the chamber reaches its constant level within 30

to 40 seconds after the apparatus is started.

With the flow of 250 liters per minute, the difficulties mentioned

above are reduced to a point where they are practically negligible.

All toxicity tests on mice were made with an exposure of ten minutes,

while dogs were exposed for thirty minutes. In case death did not occur

during exposure, the animals were kept under observation for several

days. Toxicity and all other figures are expressed in milligrams per

liter of air, though parts per million (p.p.m.) was frequently used

during the early work.

Another point of difficulty is the great individual variation in the

susceptibility of animals. This is probably greater than when the

poison is administered subcutaneously or intravenously. It necessitates

the use of a large number of animals in making a determination of the

toxicity of a gas. Again, the toxicity for different species may vary,

and as the ultimate aim is a knowledge of the toxicity for man, a

great many different species must be used. If the toxicity is widely

different for different animal species, it is hard to arrive at a

definite conclusion as to the toxicity for man.

With longer exposures than thirty minutes the lethal concentration

is usually less, there being a cumulative effect. This is not true

for hydrocyanic acid. If the concentration is not enough to kill at

once, an animal can stand it almost indefinitely. Whether the action

is cumulative or not depends on the rate at which the system destroys

or eliminates the poison. If the poison is being eliminated as fast

as received the concentration in the tissues cannot increase. It is

stated, for example, that the amount of nicotine in a cigar would

kill a man if taken in one dose. If it is spread over twenty minutes,

the destruction or elimination of the nicotine is so rapid that no

obviously bad effects are noted.

Another interesting thing about the work on poison gases is that in

most cases a preliminary exposure to less than the lethal concentration

does not seem to make the animal either more or less sensitive on a

later exposure. This is quite unexpected, because we know that with

irritating gases, especially lachrymators, men adapt themselves to

much higher concentrations than they could stand at first. In view

of the experiences of arsenic eaters, it is quite possible that the

experiments, which showed no accustoming to toxic gases, were not

continued long enough to give positive results.

Not only does the susceptibility of different animals of the same

species vary greatly for a particular gas, but the susceptibility of

different species varies greatly with different gases. Thus while the

effects of certain gases on mice are quite comparable to the effects on

man, it is very far from being true with other gases.

LACHRYMATORS

While one cannot determine the lethal concentrations of poison gases

for men, it is possible to determine the concentration that will

produce lachrymation. The threshold value is that at which two-thirds

of the observers experience irritation. The lachrymatory value is

considerably higher than the threshold value.

[Illustration: FIG. 117.—Aeration Apparatus for Testing Lachrymators.]

A very satisfactory method for determining lachrymatory values is

shown in Fig. 117. Air is measured at _A_ and bubbled through the

lachrymatory substance in _B_. The air and gas are mixed in _D_ and

pass into _E_, a gas-tight, glass-walled chamber of about 150 liters

capacity. The gas is removed through _Ef_, by suction and the volume of

the air-gas mixture measured by the flow meter, _F_.

After the apparatus has run a few minutes, and the concentration of

the gas has become constant, the subject is instructed to adjust the

mask, attached at _H_, and to tell whatever he notices just as soon

as he notices it. The operator stands in such a position that he can

manipulate the stopcock _H_ without being observed by the subject.

After breathing air for a time (_H_ is a two-way cock, connected with

the air through _J_, and to the chamber through _Eg_) both to become

accustomed to the mask and to eliminate, as far as possible, any

“psychological symptoms,” the subject is allowed to breathe the gas

mixture for a maximum of three minutes. If the expected symptoms are

produced in less than this time, the test is discontinued as soon as

they develop.

[Illustration: FIG. 118.—Type of Spray Nozzles.]

For accurate work, it is necessary to work with a pure sample which is

at least fairly volatile. Mixtures cannot be run by this method. In

this case it is necessary to volatilize each separately, passing the

vapors simultaneously into the mixing chamber _E_.

A spray method may also be used with satisfactory results. Types of

sprays are shown in Fig. 118.

ODORS

Because of the great value in detecting low concentrations of gases in

the field, it is important to know the smallest amount of a gas that

can be detected by odor. In some cases, this test is more delicate than

any chemical test yet devised.

Odors may be divided into two classes, true odors, and mild irritation.

By true odor is meant a definite stimulation of the olfactory nerve,

giving rise to a sensation which is more or less characteristic for

each substance producing the stimulation. Mild irritation defines

the sensation which is confused with the sense of smell by untrained

observers, but which is really a gentle stimulation of the sensory

nerve endings of the nose. This so-called odor of substances producing

this effect is not characteristic. Higher concentrations of these

compounds almost invariably cause a definite irritation of the nose.

Examples of true odors are the mercaptans, mustard gas, bromoacetone,

acrolein, chlorine and ammonia. Substances which cause mild irritation

are chloroacetone, methyl dichloroarsine, ethyl iodoacetate and

chloropicrin.

In making the test for odor, the same apparatus is used as for

lachrymators. The time of exposure is shortened to 30 seconds, as the

subject always detects the odor at the first or second inhalation.

In this connection the recent work of Allison and Katz (_J. Ind.

Eng. Chem._ =11=, 336, [1919]) is of interest. They have designed an

instrument, “the odorometer,” for measuring the intensity of odors

in varying concentrations in air. It is based on the principle given

above. A measured volume of air is passed through the liquid and

then diluted to a given concentration. The mixture is then passed

through a rubber tube with a glass funnel at the open end. Only one

inhalation of the mixture is used to determine the intensity of

the odor. The position of any strength of odor on the scale depends

upon the sensitiveness and judgment of the operator, but with one

person conducting the entire test, the results have been found quite

satisfactory. (See tables on pages 360 and 361.)

SKIN IRRITANTS

Substances which seem useful for producing skin burns are studied both

on animals and on man. Dichloroethyl sulfide (mustard gas) is used as a

basis of comparison. Several methods are available.

=Direct Application.= This method consists of the direct application of

the compound itself to the skin, using a definite quantity (0.005 cc.

or 0.005 mg.) over a definite area (5 square centimeters) of the skin.

With such a quantity of mustard gas a rather severe burn on animals is

produced. No precautions are taken to prevent evaporation from the skin

since it is believed that in this way the test will approximate fairly

closely the field conditions.

=Vapor Tests.= Preliminary tests with vapors of volatile compounds are

best made by placing a small amount of the material on a plug of cotton

in the bottom of a test tube enclosed in a larger test tube which acts

as an air jacket. After about an hour at room temperature the mouth of

the test tube is applied to the skin. The concentration is not known,

but one is dealing practically with saturated vapor. If an exposure

of from 30 to 60 minutes produces no effect, one is safe to assume

that the compound is not sufficiently active to be of value as a skin

irritant.

If quantitative results are desired, the apparatus shown in Fig. 119

is used. Dry air is blown through the bubbler, which is connected with

a series of glass skin applicators. The concentration is determined

in the usual way. The skin applicator consists of a small cylinder

about 1.5 to 2 cm. in diameter and about 4 cm. long with a small

glass handle attached on top. The opening is 1 cm. in diameter. When

the concentration of the gas is constant, the exposure to the skin

is made directly for any desired length of time. The skin irritant

efficiency is judged by comparing the per cent of positive responses to

approximately equal concentrations of the vapors, using mustard gas as

a standard.

TABLE I—PHYSICAL AND PHYSIOLOGICAL PROPERTIES OF CHEMICALS USED

AS STENCHES

----------------+-------+--------+-----------------+-------------+------------

| °C. | °C. | of Odor | of Vapor |

----------------+-------+--------+-----------------+-------------+------------

----------------+-------+--------+-----------------+-------------+-------------

TABLE II—RESULTS OF MEASUREMENT OF THE INTENSITY OF VARIOUS STENCHES

---------------------+---------------------------------------------

| Volumes of the Chemical, as a Perfect

| Gas, per Million Volumes of Air,

| Intensity of Odor

+------------+------+----------+--------+------

| Detectable |Faint |Noticeable| Strong Strong

---------------------+---------- -+------+----------+--------+------

Amyl acetate | 7 | 10 | 13 | 90 | 246

Ethyl acetate | 190 | 339 | 615 | 1236 | 1753

Amyl alcohol | 63 | 83 | 123 | 439 | 601

Butyric acid | 2.4 | 6 | 18 | 91 | 161

Valeric acid | 7 | 29 | 125 | 332 | 962

Ethyl ether | 1923 | 3352 | 4927 | 5825 |19982

Butyl mercaptan | 6 | 12 | 18 | 38 | 56

Isobutyl mercaptan | 3.5 | 5 | 7 | 11 | 16

Ethyl mercaptan | 18 | 35 | 73 | 141 | 198

Propyl mercaptan | 2 | 7 | 9 | 14 | 17

Amyl thioether | 0.2 | 1 | 1.6 | 1.7 | 2.2

Ethyl thioether | 3 | 12 | 29 | 61 | 74

Allyl isothiocyanate | ?2 | 3 | 6 | 8 | 50

Methyl isothiocyanate| 5 | 13 | 23 | 36 | 48

Amyl isovalerate | 1.7 | 3 | 6 | 10 | 12

Carbon tetrachloride | 718 | 1461 | 1588 | 4964 |6091

Chloroform | 674 | 1389 | 2600 | 5887 |9528

Iodoform | 1.1[35]| | | |

Nitrobenzene | 29 | 36 | 44 | 114 | 296

Phenyl isocyanide | 0.5 | 1 | 3 | 10 | 25

Pyridine | 10 | 45 | 93 | 700 | 1764

Methyl salicylate | 16.1 | 23 | 29 | 244[36]|

---------------------+------------+------+----------+--------+------

---------------------+----------------------------------------------

| Milligrams of Chemical per

| Cu. Ft. of Air,

| Intensity of Odor

+-----------+-------+----------+--------+------

---------------------+-----------+-------+----------+--------+------

Amyl acetate | 1.1 | 1.5 | 2 | 14 | 38

Ethyl acetate | 19.4 | 34.6 | 63 | 126 | 191

Amyl alcohol | 6.4 | 8.5 | 13 | 45 | 61

Butyric acid | 0.3 | 0.6 | 2 | 9 | 16

Valeric acid | 0.8 | 3.4 | 15 | 39 | 114

Ethyl ether | 165.1 | 287.7 | 423 | 500 | 1715

Butyl mercaptan | 0.5 | 1.0 | 2 | 3 | 5

Isobutyl mercaptan | 0.2 | 0.5 | 0.7 | 1 | 2

Ethyl mercaptan | 1.3 | 2.5 | 5 | 10 | 14

Propyl mercaptan | 0.2 | 0.6 | 0.8 | 1.2 | 1.6

Amyl thioether | 0.04 | 0.2 | 0.3 | 0.4 | 0.5

Ethyl thioether | 0.3 | 1.2 | 3 | 6 | 8

Allyl isothiocyanate | 0.2 | 0.3 | 0.7 | 0.9 | 6

Methyl isothiocyanate| 0.4 | 1.1 | 2 | 3 | 4

Amyl isovalerate | 0.4 | 0.5 | 1 | 2 | 2.3

Carbon tetrachloride | 128 | 260 | 283 | 886 | 1087

Chloroform | 93 | 192 | 360 | 816 | 1321

Iodoform | 0.5[37 | | | |

Artificial musk | 0.001[38]| | | |

Nitrobenzene | 4 | 5 | 6 | 16 | 42

Phenyl isocyanide | 0.06 | 0.1 | 0.4 | 1 | 3

Pyridine | 0.9 | 4 | 9 | 64 | 162

Methyl salicylate | 2.8 | 4 | 5 | 43[39 |

Oil of peppermint | 0.68 | 0.9 | 3 | 9.5 | 9.9

---------------------+-----------+-------+----------+--------+-------

---------------------+-----------------------------------------------

| Milligrams of Chemical per

| Liter of Air,

| Intensity of Odor

+-----------+------+----------+---------+------

---------------------+-----------+------+----------+---------+------

Amyl acetate | 0.039 | 0.053| 0.067 | 0.478 | 1.326

Ethyl acetate | 0.686 | 1.224| 2.219 | 4.457 | 6.733

Amyl alcohol | 0.225 | 0.300| 0.442 | 1.581 | 2.167

Butyric acid | 0.009 | 0.021| 0.066 | 0.329 | 0.580

Valeric acid | 0.029 | 0.119| 0.523 | 1.394 | 4.036

Ethyl ether | 5.833 |10.167| 14.944 |17.6667 |60.600

Butyl mercaptan | 0.018 | 0.037| 0.055 | 0.120 | 0.177

Isobutyl mercaptan | 0.008 | 0.018| 0.025 | 0.041 | 0.060

Ethyl mercaptan | 0.046 | 0.088| 0.186 | 0.357 | 0.501

Propyl mercaptan | 0.006 | 0.020| 0.028 | 0.043 | 0.054

Amyl thioether | 0.001 | 0.007| 0.0115 | 0.012 | 0.015

Ethyl thioether | 0.012 | 0.042| 0.107 | 0.223 | 0.271

Allyl isothiocyanate | 0.008 | 0.012| 0.024 | 0.030 | 0.201

Methyl isothiocyanate| 0.015 | 0.039| 0.067 | 0.108 | 0.144

Amyl isovalerate | 0.012 | 0.018| 0.039 | 0.072 | 0.082

Carbon tetrachloride | 4.533 | 9.222| 10.024 |31.333 |38.444

Chloroform | 3.300 | 6.800| 12.733 |28.833 |46.666

Iodoform | 0.018[40] | | | |

Artificial musk |0.00004[41]| | | |

Nitrobenzene | 0.146 | 0.178| 0.222 | 0.563 | 1.493

Phenyl isocyanide | 0.002 | 0.005| 0.013 | 0.042 | 0.105

Pyridine | 0.032 | 0.146| 0.301 | 2.265 | 5.710

Methyl salicylate | 0.100 | 0.145| 0.179 | 1.526[42]|

Oil of peppermint | 0.024 | 0.032| 0.109 | 0.332 | 0.348

---------------------+-----------+------+----------+---------+------

[Footnote 35: Maximum concentration obtainable.]

[Footnote 36: Maximum concentration obtainable.]

[Footnote 37: Maximum concentration obtainable.]

[Footnote 38: Maximum concentration obtainable.]

[Footnote 39: Maximum concentration obtainable.]

[Footnote 40: Maximum concentration obtainable.]

[Footnote 41: Maximum concentration obtainable.]

[Footnote 42: Maximum concentration obtainable.]

=Touch Method.= This method consists of dipping a small glass rod drawn

to a needle-like end to the depth of 1 mm. in the compound and then

quickly touching the skin. The method is qualitative only.

[Illustration: FIG. 119.—Skin Irritant Vapor Apparatus.]

=Use of Solutions.= Alcohol, kerosene, olive oil, carbon tetrachloride

and other solvents may be used for the purpose of determining

the lowest effective concentration of a substance, and for the

determination of the relative skin irritant efficiencies of various

compounds. Since the skin irritants were scarcely ever used in

this form in the field, that is, in solution, the method is not as

satisfactory as the vapor method.