Chemical warfare

by Amos A. Fries; Clarence J. West

Toxic Smoke Apparatus

It has been mentioned above that the Germans used a shell, containing solid diphenylchloroarsine and a high explosive. A 10.5 cm. shell (Blue Cross) was about two-thirds filled with cast trinitrotoluene and contained a glass bottle with 300-400 grams of toxic material. Diphenylchloroarsine was also used in shell, in solution, a mixture of phosgene and diphosgene (superpalite) being the ordinary solvent (Green Cross). Mixtures of diphenylchloroarsine and phenyldichloroarsine were also used.

In the case of high explosive shell, the use of a separate container appears to be desirable, because a mixture with the explosive seriously decreases its sensitiveness and even its destructive power. There is also a question as to the stability of such a mixture. However, 75 mm. shell containing 30 per cent diphenylchloroarsine mixed with T. N. T. gave good clouds of toxic smoke.

Toxic Smoke Candle

Two toxic smoke candles were developed by the Chemical Warfare Service, known as the B-M Toxic Smoke Candle, perfected by the Pyrotechnic Section of the Research Division, and the Dispersoid Smoke Candle, developed by the Dispersoid Section.

The B-M Toxic Smoke Candle consists of a bottle-shaped sheet steel toxic container set into a can, containing smoke mixture. The heat from the burning mixture causes the distillation of the toxic material. The toxic vapor is discharged through a nipple, screwed into the neck of the container and extending over the top of the smoke can. Steel wool is used in the toxic container to reduce the violent boiling and spattering of the material. A small amount of steel wool, held in place by a wire screen, is also used in the nipple for the same purpose. The toxic container is sealed by a fusible metal plug, melting at 90° C., cast into a retainer at the base of the nipple. The fusible plug melts upon the first application of heat and allows free passage of the vapor into the smoke cloud. The ignition of the apparatus is effected by means of a simple match head and an accompanying scratcher.

Fig. 102.—Toxic Smoke Cloud from 500 D. M. Candles.

The candles were placed in 5 parallel rows which were 2 yards apart, each row containing 100 candles on a 100 yard front. The total time of active smoke emission was 23 minutes.

The first evolution of smoke occurs about 10 seconds after the first appearance of flame. About one minute after ignition the toxic material will begin to distill into the smoke cloud and this will continue for about four minutes. The burning of the candle should be complete in about six minutes.

Dispersoid CandleBritish Candle

Fig. 103.—Comparison of Dispersoid and British D. M. Candles.

The Dispersoid Toxic Smoke Candle differs from the B-M candle in that the toxic container is not used. A mixture of smokeless powder and the toxic material (diphenylchloroarsine or D. M., an arsenical obtained from arsenic trichloride and diphenylamine) is filled directly into the container, a cylindrical can 3.5 inches in diameter and 9 inches high made from 27 gauge sheet metal, and packed under a total pressure of 2,500 pounds. The top of the candle is a metal cover, containing the match head scratcher, which is separated from the match head by a Manila paper disc. These are the same as those used in the B-M candle. The candle has a total weight of about 4.25 pounds, of which 3.6 pounds are the smoke mixture, containing about 1.3 pounds of toxic material.

In operating the candles, the cover is removed and the match head ignited by friction with the scratcher. The match head burns through the cardboard and ignites the powder. The heat and gas produced by the combustion of the powder vaporizes the particles of the toxic material and carries the vapors out through the orifices at a high velocity whereupon they recondense to form a smoke. The rapid emission of the vapors through the orifice prevents any possibility of their ignition.

The time before good emission of smoke takes place after the ignition of the match tip of a candle is 30 seconds. The average time of vigorous smoke emission is from four to five minutes. The result of a field test with the dispersoid candle is shown in [Fig. 102]. A comparison of a British and a Dispersoid candle is shown in [Fig. 103]. It should be stated that this may not have been a fair test as only one British candle was available for the comparative test.

CHAPTER XVIII
SMOKE FILTERS

The first types of the Standard Box Respirator contained cotton pads, which sufficed to remove the ordinary smoke of the battlefield and even that from the earlier toxic materials. Improved methods of producing toxic smokes, by means of which smaller particles were obtained, led, early in 1918, to the recognition of the need of improved protection against these smokes. The first attempts to meet this need consisted in improving the filtering qualities of these pads. It was soon found, however, that to make better filter pads would greatly increase the total resistance of the canister. This was highly undesirable, since the resistance of the ordinary canister was already so high as to be very uncomfortable. To overcome this objection, some of the early designs of filter canisters were provided with a mechanical valve, which could be operated by hand, to by-pass the air around the filter when the canister was used against gas alone, or so set as to make the air pass through the filter when smoke was feared. This introduced a factor of uncertainty among the men during a gas attack, since each man must decide for himself whether smoke was present. This reason alone was sufficient for discarding this design.

A preliminary study of the situation indicated that any filter for fine smoke particles must have a high resistance per unit of area, but that the total resistance must be comparatively low. In order to secure the large area necessary to bring the total resistance within reason, the experimental work was developed along three lines: The formation of a filter into a bag, cup, or jacket to surround the outside of the canister; the use of an arrangement sufficiently compact to go inside the canister; and the use of a filter as a separate unit, to be attached to the canister by an air connection.

A survey of the possible filtering materials indicated that only two offered promise, namely, paper and felt.