CARBON MONOXIDE
Carbon monoxide, because of its cheapness, accessibility and ease of
manufacture, has been frequently considered as a possible war gas.
Actually, it appears never to have been used intentionally for such
purposes. There are several reasons for this. First, its temperature of
liquefaction at atmospheric pressure is -139° C. This means too high a
pressure in the bomb or shell at ordinary temperatures. Secondly, the
weight of carbon monoxide is only slightly less than that of air, which
keeps it from rolling into depressions, dugouts and trenches, as in
the case of ordinary gases, and also permits of its rather rapid rise
and dissipation into the surrounding atmosphere. A third reason is its
comparatively low toxic value, which is only about one-fifth that of
phosgene. However, as it can be breathed without any discomfort, and as
it has some delay action, its lack of poisonous properties would not
seriously militate against its use were it not for the other reasons
given.
It is, nevertheless, a source of serious danger both in marine and
land warfare. Defective ventilation in the boiler rooms of ships
and fires below decks, both in and out of action, are especially
dangerous because of the carbon monoxide which is produced. In one of
the naval engagements between the Germans and the English, defective
high explosive shell, after penetrating into enclosed portions of the
ship, evolved large quantities of carbon monoxide and thus killed some
hundreds of men. On shore, machine gun fire in enclosed spaces, such
as pill boxes, and in tanks, liberates relatively large quantities of
carbon monoxide. Similarly, in mining and sapping work, the carbon
monoxide liberated by the detonation of high explosives constitutes one
of the most serious of the difficulties connected with this work and
necessitated elaborate equipment and extensive military training in
mine rescue work.
The removal of carbon monoxide from the air is difficult because of its
physical and chemical properties. Its low boiling point and critical
temperature makes adequate adsorption at ordinary temperatures by the
use of an active absorbent out of the question. Its known insolubility
in all solvents similarly precludes its removal by physical absorption.
After extensive investigation two absorbents have been found.[24] The
first of these consists in a mixture of iodine pentoxide and fuming
sulfuric acid, with pumice stone as a carrier. Using a layer 10 cm.
deep and passing a 1 per cent carbon monoxide air mixture at the rate
of 500 cc. per minute per sq. cm. cross section, a 100%-90% removal
of the gas could be secured for two hours at room temperature and
almost as long at 0° C. The reaction is not instantaneous, and a brief
induction period always occurs. This may be reduced to a minimum by the
addition of a little iodine to the original mixture.
[Footnote 24: Complete details of this work may be found in _J. Ind.
Eng. Chem._, =12=, 213 (1920).]
The sulfur trioxide given off is very irritating to the lungs, but
by the use of a layer of active charcoal beyond the carbon monoxide
absorbent, this disadvantage was almost completely eliminated. However,
sulfur dioxide is slowly formed as a result of this adsorption and
after prolonged standing or long-continued use of the canister at a
high rate of gas flow gives serious trouble.
Considerable heat is given off in the reaction and a cooling attachment
was required. The most satisfactory device was a metal box filled
with fused sodium thiosulfate pentahydrate, which absorbed a very
considerable amount of the heat.
Still a further disadvantage was the fact that the adsorbents became
spent by use, even in the absence of carbon monoxide, since it absorbed
enough moisture from the air of average humidity in several hours, to
destroy its activity.
The difficulties mentioned were so troublesome that this absorbent was
finally supplanted by the more satisfactory oxide absorbent described
below.
[Illustration: FIG. 39.—Diagram of Carbon Monoxide Canister, CMA3.]
The metallic oxide mixture was the direct result of an observation that
specially precipitated copper oxide with 1 per cent silver oxide was an
efficient catalyst for the oxidation of arsine by oxygen. After a study
of various oxide mixtures, it was found that a mixture of manganese
dioxide and silver oxide, or a three component system containing
cobaltic oxide, manganese dioxide and silver oxide in the proportion of
20:34:46 catalyzed the reaction of carbon monoxide at room temperature.
The studies were extended and it was soon found that the best catalysts
contained active manganese dioxide as the chief constituent. This was
prepared by the reaction between potassium permanganate and anhydrous
manganese sulfate in the presence of fairly concentrated sulfuric acid.
It also developed that the minimum silver oxide content decreased
progressively as the number of components increased from 2 to 4. The
standard catalyst (Hopcalite) finally adopted for production consisted
of 50 per cent manganese dioxide, 30 per cent copper oxide, 15 per cent
cobaltic oxide and 5 per cent silver oxide. The mixture was prepared
by precipitating and washing the first three oxides separately, and
then precipitating the silver oxide in the mixed sludge. After washing,
this sludge was run through a filter press, kneaded in a machine, the
cake dried and ground to size. While it is not difficult to obtain a
product which is catalytically active, it requires a vigorous control
of all the conditions and operations to assure a product at once
active, hard, dense and resistant as possible to the deleterious action
of water vapor.
[Illustration: FIG. 40.—Tanks and Press for Small Scale Manufacture of
Carbon Monoxide Absorbent.]
Hopcalite acts catalytically and therefore only a layer sufficiently
deep to insure close contact of all the air with the catalyst is
needed. One and a half inches (310 gm.) were found ample for this
purpose.
The normal activity of Hopcalite requires a dry gas mixture. This was
secured by placing a three-inch layer of dry granular calcium chloride
at the inlet side of the canister.
Because of the evolution of heat, a cooling arrangement was also used
in the Hopcalite canisters.
The life of this canister was the same irrespective of whether its use
was continuous or intermittent. The higher the temperature the longer
the life because Hopcalite is less sensitive to water vapors at higher
temperatures. Since, if the effluent air was sufficiently dried, the
Hopcalite should function indefinitely against any concentration of
carbon monoxide, the life of the canister is limited solely by the life
of the drier. Therefore the net gain in weight is a sure criterion of
its condition. After many tests it was determined that any canister
which had gained more than 35 grams above its original weight should
be withdrawn. The canisters, at the time of breakdown, showed a gain
in weight varying between 42 and 71 grams, with a average of 54 grams.
It is really, therefore, the actual humidity of the air in which the
canister is used that determines its life.
[Illustration: FIG. 41.—Navy Head Mask and Canister.]