CHAPTER XII

DEVELOPMENT OF THE GAS MASK

While in ordinary warfare the best defense against any implement of war is a vigorous offense with the same weapon, Chemical Warfare presents a new point of view. Here it is very important to make use of all defensive measures against attack. Because of the nature of the materials used, it has been found possible to furnish, not only general protection, but also continuous protection during the time the gas is present.

The first consideration in the protection of troops against a gas attack is the provision of an efficient individual protective appliance for each soldier. The gas attack of April 22, 1915 found the Allies entirely unprepared and unprotected against poisonous gas. While a few of the men had the presence of mind to protect themselves by covering their faces with wet cloths, the majority of them became casualties. Immediately steps were taken to improvise protective devices among which were gags, made with rags soaked in water or washing soda solution, handkerchiefs filled with moist earth, etc. One suggestion was to use bottles with the bottom knocked off and filled with moist earth. The breath was to be taken in through the bottle and let out through the nose; but as bottles were scarce and few of them survived the attempt to get the bottom broken off, the idea was of no value.

The first masks were made by the women of England in response to the appeal by Lord Kitchener; they consisted of cotton wool wrapped in muslin or veiling and were to be kept moist with water, soda solution or hypo.

ENGLISH MASKS

=The Black Veiling Respirator.= The first form of the English mask is known as the Black Veiling respirator and consisted of cotton waste enclosed in a length of black veiling. The waste was soaked in a solution of:

Sodium thiosulphate 10 lbs. Washing soda 2.5 lbs. Glycerine 2 lbs. Water 2 gals.

The glycerine was put in to keep the respirator moist, thus obviating the need for dipping before use.

[Illustration: FIG. 42.—Early Gas Protection.]

The respirator was adjusted over the mouth and nose, the cotton waste being molded to the shape of the face and the upper edge of the veiling pulled up so as to protect the eyes. These respirators were used in the attacks of May 10th and 12th, 1915 and were reasonably efficient against the low concentration of chlorine then used; they were difficult to fit exactly to the face, which resulted in leakage. The cotton waste often became lumpy and had to be shredded out or discarded.

=The Hypo Helmet.= The next development of the British protection was the so-called Hypo helmet. This is said to have resulted from the suggestion of a Canadian sergeant that he had seen a German pulling a bag over his head during a gas attack. It consisted of a flannel bag soaked in the same solution as was used for the veiling respirator and was fitted with a pane of mica as a window. The helmet was tucked down inside the jacket which was then buttoned up tightly around the neck. As may be seen from Figure 43, this would not prove very satisfactory with the American type of uniform.

This helmet had many advantages over the veiling respirator but the window often became cracked or broken from the rough treatment in the trenches. Later the mica was replaced by celluloid and still later by glass eyepieces set in metal rings. These were very effective against chlorine in the field.

=The P and PH Helmets.= During the summer of 1915 it became evident that phosgene-chlorine mixtures would be used in gas attacks and it was therefore necessary to provide protection against this. The hypo helmet, which offered no protection against phosgene, was soaked in an alkaline solution of sodium phenolate (carbolic acid) containing glycerine, and with this new form of impregnation was called the P helmet. It protected against 300 parts of phosgene in a million of air. Since this solution attacks flannel, two layers of flannelette were used. The helmet was further improved by the addition of an expiratory valve, partly to prevent the man from breathing any of his own breath over again and partly to prevent the deterioration of the alkali of the mask by the carbon dioxide of the expired air.

The protection was later further increased by the addition of hexamethylenetetramine, and this mask is known as the PH helmet. This increased the protection to 1,000 p.p.m.

The early types of helmet offered no protection against lachrymators. For this purpose goggles were used, the later types of which had glass eyepieces and were fitted around the eyes by means of rubber sponge. While intended for use only after a lachrymatory bombardment, the troops frequently used them during and after an ordinary gas attack when the mask should have been worn. Consequently they were withdrawn.

The PH helmet was unsatisfactory because of the following reasons:

(1) It was warm and stuffy in summer; (2) It deteriorated upon exposure to air; (3) It was incapable of further development; (4) It had a peculiar odor and, when wet, frequently burned the foreheads of the men; (5) It offered practically no protection against lachrymators.

[Illustration: FIG. 43.—Method of Wearing the P. H. Helmet.]

[Illustration: FIG. 44.—Early Type of Standard (British) Box Respirator (S. B. R.)]

=Box Respirator.= The increasing concentration of gas from cylinder attacks and the introduction of shell, with such gases as chloropicrin and superpalite, led, early in 1916, to very definite and constructive efforts on the part of the British to increase the protection offered by the mask. The result was a “polyvalent” respirator of the canister type (the Standard Box Respirator). This mask was probably the result of experience with oxygen apparatus in mine rescue work. The lines on which this canister was modeled involved the use of a canister filled with highly sensitive absorbent charcoal mixed with or alternating in layers with oxidizing granules of alkaline permanganate. It was the result of innumerable experiments, partly conducted in France but mostly in England under the direction of the late Lieut. Col. Harrison, who was almost entirely responsible for the wonderful production of this respirator.

The respirator (Figure 44) consisted of the canister mentioned above, which is attached by a flexible tube to a facepiece or mask. The facepiece is made of rubberized fabric and fits the face so that there is little or no leakage. This is secured by means of tape and elastic bands which fit over the head. The nose is closed by means of clips, which are wire springs with rubbered jaws covered with gauze (Fig. 45). Breathing is done through a mouthpiece of rubber; the teeth close on the rubber tabs and the rubber flange lies between the teeth and the lips. The expired air finds exit through a rubber flutter valve in an angle tube just outside the mask. This arrangement furnishes a double line of protection; if the face piece is punctured or torn, gas-containing air cannot be breathed as long as the noseclip and mouthpiece are in position.

The early English canister was packed with 675 cc. of 8-14 mesh war gas mixture, 40 per cent of which was wood charcoal and 60 per cent reddish brown soda-lime granules. The metal dome at the bottom of the can was covered with a thin film of cotton. At two-thirds of the distance to the top was placed a paper filter and a heavy wire screen which differs from our heavy screen in that it is more loosely woven. The mixture was covered with a cotton filter pad and a wire screen, over which was placed the wire spring.

The use of this mask ensures that all the air breathed must enter the lungs through the canister. This air passage is entirely independent of leaks in the facepiece, due either to a poor fit about the face or to actual leakage (from a cut or tear) of the fabric itself. The facepiece is readily cleared of poison gases which may leak in. This is accomplished by taking a full inspiration, releasing the noseclip, and exhaling through the nose, which forces the air out around the edges of the facepiece.

On the other hand, this type of mask possesses a number of very obvious disadvantages, particularly from a military point of view:

The extreme discomfort of the facepiece. This discomfort arises from a number of causes certain of which are inherent in this type of mask, among them being: (_a_) the noseclip, (_b_) the mouthpiece, and (_c_) the lack of ventilation within the facepiece chamber.

Aside from the actual physical discomfort of the noseclip and mouthpiece, which becomes intense after long periods of wearing, this combination forces upon the wearer an unnatural method of respiration to which it is not only difficult to become accustomed, but which also causes extreme dryness of the throat. The mouthpiece greatly increases salivation and as swallowing is rather more difficult with the nose closed, this adds another extremely objectionable feature.

[Illustration: FIG. 45.—Interior of S. B. R., Showing Cotton Wrapped Noseclips.]

[Illustration: FIG. 46.—French M-2 Mask.]

The lack of ventilation in the facepiece chamber entraps the heat radiating from the face and retains the moisture which is constantly evaporating from the skin. This moisture condenses on the eyepieces, and even if cleared away by the use of a so-called anti-dimming paste, usually makes vision nearly impossible.

FRENCH MASKS

=M-2 Mask.= The early protection of the French Army was obtained from a mask of the type M-2 (Fig. 46).

This mask consists of a number of layers of muslin impregnated with various absorbent chemicals. A typical mask was made up of 20 layers of cheesecloth impregnated with _Greasene_ and 20 layers impregnated with _Complexene_. These solutions were made up as follows:

Complexene: 39.0 lbs. Hexamethylenetetramine 37.5 lbs. Glycerine 27.5 lbs. Nickel sulfate (NiSO₄.7 H₂O) 11.8 lbs. Sodium carbonate (Na₂CO₃) Water

Greasene: 107.0 lbs. Castor oil 81.0 lbs. Alcohol (95%) 10.7 lbs. Glycerine (90%) 3.1 lbs. Sodium hydroxide (NaOH)

This mask fits the face tightly and as a consequence the inhaled air can be obtained only by drawing it through the pores of the impregnated fabric. There is no outlet valve. The exhaled air makes its escape through the fabric. The eyepieces are made of a special non-dimming celluloid. The mask is protected from rain by a flap of weather proof fabric, which also protects the absorbent chemicals from deterioration.

At the beginning of the war the United States experimented considerably with the French mask. Several modifications of the impregnating solutions were suggested, as well as methods of application. One of these was to separate the components of the complexene solution and impregnate two separate layers of cloth; this would make a three-layer mask. In view of the phosgene which was in use at that time, the following arrangement was suggested:

20 layers of hexamethylenetetramine, 10 layers of nickel sulfate-sodium carbonate, 10 layers of greasene.

This arrangement was more effective than the original French mask and offered the following protection when tested against the following gases (concentration 1 to 1,000, rate 30 liters per minute):

Phosgene 65 minutes Hydrocyanic acid 60 minutes Chlorine 60 minutes

[Illustration: FIG. 47.—Interior View of M-2 Mask.]

[Illustration: FIG. 48.—French Artillery Mask, Tissot Type.]

=Tissot Mask.= The French deserve great credit for their development of the Tissot type mask. This was first issued to artillerymen, stretcher bearers, and certain other special classes of soldiers to furnish them with protection and yet enable them to work with greater efficiency because of the decrease in resistance to breathing. The mask (Fig. 48) resembles the British box respirator in that it consists of a canister and rubber facepiece, but differs in that the mouthpiece and noseclip are lacking. The inhaled air enters the mask from two tubes which open directly under the eyepieces and allow the air to sweep across them. This removes, by evaporation, the condensed moisture of the breath from the eyepieces, which otherwise would obstruct the vision. The circulation of the fresh air in the mask also removes and dilutes lachrymatory gases which may filter through the mask. The exhaled air escapes through a simple outlet valve. This type of mask is advantageous because:

(1) The facepiece is tight and comfortable. (2) The eyepieces do not become dimmed. (3) There is no difficulty in speaking. (4) Salivation is eliminated because of the absence of the mouthpiece. (5) It is generally more comfortable than the box respirator.

This mask, however, was made of thin rubber of great flexibility which, while affording a perfect fit, did not possess sufficient durability to recommend it as the sole defense of the wearer.

The canister is markedly different from all other canisters described in this chapter in that a highly hygroscopic chemical absorbent is used. An approximate determination showed about 70 per cent sodium hydroxide. The use of caustic soda in the canister is made possible by the intermixing of steel wool with the granules of caustic. A layer of absorbent having the appearance of vegetable charcoal is placed at the top of the canister.

The canister has the shape of a rectangular prism 8 × 6½ × 2½ inches; and, owing to the use of steel wool, is large in proportion to the weight of absorbent contained. Valves are supplied which prevent exhalation through the canister. When not in use the opening in the bottom of the canister is plugged with a rubber stopper to protect the absorbents from moisture. The canister is carried against the body and is connected to the facepiece with a flexible rubber-fabric tube.

=A. R. S. Mask (Appareil Respiratoire Special).= One of the latest types of French mask is the so-called A. R. S. mask, which is based upon, or at least resembles closely, the German mask. This is a frame mask made from well rubberized balloon material, provided on the inside with a lining of oiled or waxed linen and fitted with a drum which is screwed on. The mask is provided with eyepieces of cellophane, fastened by metal rings into rubber goggles, which are sewed in the mask. A metal mouth-ring is tied in the mask with tape. This ring is placed somewhat higher than in the German mask, in this way reducing the harmful space under the mask. An inlet and outlet valve is placed in the mouth-ring; the first is of mica while the other, which is in direct communication with the interior of the mask, is of rubber. On the inside of the mask, in front of the valves, a baffle is sewed in, whereby the inhaled air is forced to pass in front of the eyepieces to prevent dimming and, at the same time, condensed vapor is prevented from entering the valves.

[Illustration: FIG. 49.—French A. R. S. Mask.]

The mask or head straps are arranged in the same way as on the latest M-2 mask, i.e., one elastic band is placed across the top of the head and the other across the back; the two are joined by an elastic. Below these two straps is an adjustable elastic neck band. The drum is made of metal similar in shape to the German drum and fits in the mouth-ring by means of a thread. It is made tight by a rubber ring as in the German mask. The thread differs from that on the German mask, making an interchange of canisters impossible. The canister or drum includes a bottom screen, springs and wire screens between the layers. It is closed by a perforated bottom. There are three layers. On the top is a thin layer of absorbent cotton. Beneath this is a central layer of charcoal, which is a little finer than the German charcoal. The lower layer consists of soda-lime, mixed with charcoal and zinc oxide and moistened with glycerine.

GERMAN MASK

The early type of German mask probably served as the model for the French A. R. S. mask. The facepiece was made of rubber, which was later replaced by leather because of the shortage of rubber. The following is a good description of a typical German facepiece:

“The facepiece of the German mask was made of one piece of leather, with seams at the chin and at the temples, giving it roughly the shape of the face. The leather was treated with oil to make it soft and pliable, also to render it impervious to gases. The dressed surface was toward the inside of the mask. A circular steel plate, 3 inches in diameter, was set into the facepiece just opposite the wearer’s nose and mouth, with a threaded socket into which the drum containing the absorbents screwed. A rubber gasket (synthetic?) held in place by a sort of pitch cement, secured a gas-tight joint between the drum and the facepiece. There were no valves, both inhaled and exhaled air passing through the canister. The eyepieces were inserted by means of metal rims with leather washers, and were in two parts: (_a_) a permanent exterior sheet of transparent material (‘cellon’) resembling celluloid, and (_b_) an inner removable disc which functioned as an anti-dimming device. This latter appeared to be of ‘cellon’ coated on the side toward the eye with gelatin, and was held in position by a ‘wheel’ stamped from thin sheet metal, which screwed into the metal rim of the eyepiece from the inside. The gelatin prevented dimming by absorbing the moisture, but wrinkled and blistered and became opaque after a few hours’ use, and could not be changed without removing the mask. The edge of the facepiece all around was provided with a bearing surface consisting of a welt of finely woven cloth about one inch wide sewed to the leather. In some instances this welt was of leather of an inferior grade. The edge of the facepiece was smoothed over by a coat of flexible transparent gum, probably a synthetic compound.”

[Illustration: FIG. 50.—German Respirator.]

[Illustration: FIG. 51.—The German Respirator.]

1. Smoke Filter Extension. 2. Canister. 3. Ring for Protecting Eye Piece. 4. Anti-dimming Disc Envelope. 5. Carrying Case. 6. Cloth Wallet for Extra Canister (1918). 7. Can for Extra Canister (1916). 8. Assembled Respirator. 9. Face Piece. 10. Anti-dimming disc.

=German Canister.= The general appearance of the canister (Sept., 1916 Type) is that of a short thick cylinder slightly tapered and having at the smaller end a threaded protrusion or neck by which it is screwed onto the facepiece. The cylinder is about 10 cm. in diameter and about 5 cm. in length. In the canister are three layers of absorbents of unequal thickness separated by disks of fine mesh metal screen. The canister is shipped in a light sheet iron can 10 cm. in diameter and 8 cm. high. The can is shellacked and is lined with paper packing board. The container is made air-tight by sealing with a strip of adhesive tape.

[Illustration: FIG. 52.—Cross Section of 1917 and 1918 German Canisters.]

ABSORBENTS.

Absorbent. Composition. Weight. Volume. 1917. No. 1. Chemical Absorbent. 66 gr. 105 cc. No. 2. Impregnated Charcoal. 36 gr. 85 cc. No. 3. Chemical Absorbent. 15 gr. 45 cc. 1918. No. 1. Impregnated Charcoal. 58 gr. 185 cc. No. 2. Chemical Absorbent. 29 gr. 45 cc.

Total Volume of Absorbents, 1917, 235 cc. = 14.3 cu. in. 1918, 230 cc. = 14.0 cu. in. Total Weight of Absorbents, 1917, 117 gr. 1918, 87 gr. Volume of Air Space above Absorbents = 50 cc. = 3.1 cu. in.

=Body.= The body of the canister is made of sheet metal (probably iron), which is protected on the outside with a coat of dark gray paint and on the inside with a japan varnish. For ease in assembling the sides of the canister have a gentle taper, and are formed so as to supply a seat for each of the follower rings. The protrusion or neck has about six threads to the inch, the pitch of the screw being 4 mm. The lower part of the body is rolled so as to give a finished edge, and the upper part of the cylinder is grooved to receive the top support.

The first screen is double, consisting of a coarse top screen five to six mesh, per linear inch, and immediately below, a finer screen of 30-40 mesh, per linear inch. The top support is a rigid ring of metal with two cross arms, which give added, strength to the ring and support to the screens. It springs into a groove at the top of the body and forms the support for the contents of the canister. Both screens are made of iron wire and the top support is made of iron (probably lightly tinned).

The second screen, which separates the second and third absorbents, is double, consisting of two disks of 30-40 mesh iron screen. Both screens are held in place by a follower ring.

The third screen is single, but otherwise it is exactly similar to the second screen. It serves to keep separate the layers of absorbents No. 1 and No. 2.

The fourth screen (30-40 mesh) is made of iron wire and is held to the bottom support by six cleats which are punched from the body of the support. The bottom support is simply a flanged iron cover for the bottom of the canister. It is punched with 79 circular holes each 4 mm. in diameter and is painted on the outside to match the body of the canister. The screen and the inside of the bottom support or cover are coated with a red paint.

AMERICAN MASK

At the entrance of the United States into the war, three types of masks were available: the PH helmet, the British S. B. R. and the French M-2 masks. Experiments were made on all three of these types, and it was soon found that the S. B. R. offered the greatest possibilities, both as regards immediate protection and future development. During the eighteen months which were devoted to improvement of the American mask, the facepiece underwent a gradual evolution and the canister passed through types _A_ to _L_, with many special modifications for experimental purposes. The latest development consisted in an adaptation of the fighting mask to industrial purposes. For this reason a rather detailed description of the construction of the facepiece and of the canister of the respirator in use at the close of the war (R. F. K. type) may not be out of place. The mask now adopted as standard for the U. S. Army and Navy is known as the Model 1919 American mask, with 1920 model carrier, and will be described on page 225.

[Illustration: FIG. 53.—Diagrammatic Sketch of Box Respirator Type Mask.]

=Facepiece.= The facepiece of the R. F. K. type Box Respirator is made from a light weight cotton fabric coated with pure gum rubber, the finished fabric having a total thickness of approximately ¹/₁₆ inch. The fit of the facepiece is along two lines—first, across the forehead, approximately from temple to temple; second, from the same temporal points down the sides of the face just in front of the ears and under the chin as far back as does not interfere with the Adam’s apple. In securing this fit, the piece of stock for the facepiece is died out of the felt and pleated up around the edges to conform to this line. After this pleating operation, the edges of the fabric are stitched to a binding frame similar to a hat-band made up of felt or velveteen covered with rubberized fabric. All the stitching and joints in the facepiece are rendered gas-tight by cementing with rubber cement. This facepiece is made in five sizes ranging from No. 1 to No. 5, with a large majority of faces fitted by the three intermediate sizes, 2, 3, 4.

=Harness.= The function of the harness is to hold the mask on the face in such a way as to insure a gas-tight fit at all points. Because of the great variations in the conformation of different heads, this problem is not a simple one. Probably, the simplest type of harness, as well as the one which is theoretically correct, consists of a harness in which the line of fit across the forehead is extended into an elastic band passing around the back of the head, while the line of fit around the side of the face and chin is similarly extended into another elastic tape passing over the top of the head; these should be held in place by a third tape, preferably non-elastic, attached to the mask at the middle of the forehead and to the middle points of the other tapes at a suitable distance to hold them in their proper positions.

The discomfort of the earlier types of harness has been remedied, in a large measure, by the development of a specially woven elastic web which, for a given change in tension, allowed more than double the stretch of the commercial weaves. There is still much room for valuable work in developing a harness which will combine greater comfort and safety. The following points should always be observed in harness design:

(1) The straps should pull in such a direction that as large a component as possible of the tension of the strap should be available in actually holding the mask against the face.

(2) The number of straps should be kept to a minimum in order to avoid tangling and improper positioning when put on in a hurry by an inexperienced wearer.

=Eyepieces.= One of the most important parts of the gas mask, from the military point of view, is the eyepiece. The primary requirement of a good eyepiece is that it shall provide a minimum reduction in clarity of vision with a maximum degree of safety to the wearer. The clarity of vision may be affected in one of several ways: (1) by abrasion of the eyepieces under service conditions; (2) irregularities in the surface and thickness of the eyepiece, causing optical dispersion; (3) absorption of light by the eyepiece itself; (4) dimming of the eyepieces due to condensation of moisture radiating from the face or in the exhaled air.

Three types of eyepieces were used but by the end of the war the first two types had been abandoned.

(1) Ordinary celluloid.

(2) Various hygroscopic forms of celluloid, known as non-dimming eyepieces.

(3) Various combinations of glass and celluloid, known as non-breakable eyepieces.

Celluloid was used first, due to its freedom from breakage. It is not satisfactory because it is rapidly abraded in use, turns yellow, thus increasing its light absorption, has relatively uneven optical surfaces and becomes brittle after service.

The various forms of non-dimming lenses function by absorbing the water which condenses on their surfaces, either by combining individual drops into a film which does not seriously impair vision, by transmitting it through the surface and giving it off on the exterior or by a combination of these mechanisms. With the exception that they are non-dimming, they are open to all the objections of the celluloid eyepiece and, as a matter of fact, were never tried out in the field.

The so-called non-breakable eyepieces are formed by cementing together a layer of celluloid between two layers of glass.[25] This results in an almost perfect eyepiece. Any ordinary blow falling upon such an eyepiece does no more than crack the glass, which remains attached to the celluloid coating. Except in extreme cases, the celluloid remains unbroken and there is relatively slight danger of a cracked eyepiece of this sort leaking gas.

[Footnote 25: So-called “Triplex” glass.]

In the matter of flying fragments, the type of eyepiece consisting of a single layer of celluloid and glass with the celluloid placed next to the eye, has probably a slight advantage over the type in which there is glass on both sides. However, the superior optical surface of the latter type, coupled with its greater freedom from abrasion of the surface led to the adoption of this type known as “triplexin” in the mask produced in the later part of the American manufacturing program. It should be pointed out in connection with this type of eyepiece that it is possible to make it as perfect optically as desired by using the better grades of glass. While the optical properties of these eyepieces undoubtedly suffer somewhat with age, due to the discoloration of the celluloid, it can be safely said that this material, located as it is between the layers of glass and relatively little exposed to atmospheric conditions, will probably be far less affected in this way than is the ordinary celluloid eyepiece.

[Illustration: FIG. 54.—American Box Respirator, Showing Improved Rubber Noseclip.]

The position of the eyepiece is very important; the total and the binocular fields of vision should be kept at a maximum.

=noseclip.= The noseclip is probably the most uncomfortable feature of the types of mask used during the War. While a really comfortable nose pad is probably impossible, the comfort of the clip was greatly improved by using pads of soft rubber and springs giving the minimum tension necessary to close the nostrils.

=Mouthpiece.= The design of the mouthpiece should consider the size and shape of the flange which goes between the lips and teeth; this should be such as to prevent leakage of gas into the mouth and should reduce to a minimum any chafing of the gums. The opening through the mouthpiece is held distended at its inner end by a metallic bushing to prevent its collapse, if, under stress of excitement, the jaws are forced over the flange and closed. Rubber has proved a very satisfactory material for this part of the facepiece.

=Flexible Hose.= The flexible hose leads from the angle tube to the canister. This should combine flexibility, freedom from collapse, and extreme physical ruggedness. These specifications are met successfully by the stockinette-covered corrugated rubber hose. The angular corrugations not only give a high degree of flexibility but are extremely effective in preventing collapse. The flexibility gained by this construction is not only lateral but also longitudinal; a hose having a nominal length of 10 inches functions successfully between lengths of 8 and 12 inches. The covering of stockinette, which is vulcanized to the rubber in the manufacturing process, adds materially to the mechanical strength by preventing incipient tears and breaks.

=Exhalation Valve.= The exhalation valve allows the exhaled air to pass directly to the outside atmosphere. (This valve is not found on the German mask.) This valve has the following advantages:

(1) It tends to reduce very materially the dead air space in the mask.

(2) It prevents deterioration of the absorbent on account of moisture and carbon dioxide of the expired air.

(3) It reduces the back pressure against expiration, since it is unnecessary to breathe out against the resistance of the canister.

The disadvantage, which may under certain conditions be very serious, is that, if for any reason the valve fails to function properly, inspiration will take place through the valve. It can be readily seen that any failure of this nature will allow the poisonous atmosphere to be drawn directly into the lungs of the wearer.

The type of valve generally used is shown in Fig. 55, which shows one of these valves mounted and unmounted. While it is rather difficult to give a clear description of its construction, the valve may be considered as a flattened triangular sack of rubber, whose altitude is two or three times the base and from which all three corners have been clipped, each giving openings into the interior of the sack. The opening at the top is slipped over the exhalation passage of the angle tube, and the air passes out through the other two corners. Closure is obtained by the combination of two factors,—first, the difference in atmospheric pressure, and second, the tension due to mounting a section which has been cured in the flat over an elliptical opening.

[Illustration: FIG. 55.—American Type Exhale Valve, Mounted and Unmounted.]

In order to protect the flutter valve from injury and from contact with objects which might interfere with its proper functioning, the later types of valve were provided with a guard of stamped sheet metal.

CANISTERS

During the development of the facepiece, as discussed above, the American canister underwent changes in design which have been designated as _A_ to _L_. These changes were noted by the different colored paints applied to the exterior of the canister.

Type _A_ canister was exactly like the British model then in use, except that it was made one inch longer because it was realized that the early absorbents were of poor quality. The canister was made of beaded tin plate and was 18 cm. high. The area of the flattened oval section was 65 sq. cm. In the bottom was a fine wire dome 3.4 cm. high. The valve in the bottom was integral with the bottom of the container, there being no removable plug for the insertion of the check valve. The absorbents were held in place by a heavy wire screen on top and by two rectangular springs.

[Illustration: FIG. 56.—American Canister, Type _A_.]

Inhaled air entered through the circular valve at the bottom of the canister, passed through the absorbents and through a small nipple at the top.

The filling consisted of 60 per cent by volume of wood charcoal, developed by the National Carbon Co., and 40 per cent of green soda lime, developed and manufactured by the General Chemical Company, Easton, Pa. The entire volume amounted to 660 cc. The early experiments with this volume of absorbent showed that ⅖ soda-lime was the minimum amount that could be used and still furnish adequate protection against the then known war gases. It was, therefore, decided to use ⅖ soda-lime and ⅗ charcoal by volume and this proportion has been adhered to in all of the later types of canisters. It is interesting to note that these figures have been fully substantiated by the later experimental work on canister filling.

The charcoal and soda-lime were not mixed but arranged in five layers of equal volume, each layer, therefore, containing 20 per cent of the total volume. The layers were separated by screens of crinoline. At the top was inserted a layer of terry cloth, a layer of gray flannel, and two steel wire screens. The cloth kept the fine particles of chemicals from being drawn into the throat of the person wearing the mask.

This canister furnished very good protection against chlorine and hydrocyanic acid and was fairly efficient against phosgene, but it was useless against chloropicrin. These canisters were never used at the front, but served a very useful purpose as experimental canisters and in training troops.

It was soon found that better protection was obtained if the absorbents were mixed before packing in the canister. This procedure also simplified the method of packing and was used in canister _B_ and following types. Among other changes introduced in later types were: The integral valve was replaced by a removable check valve plug which enabled the men in the field to adjust the valve in case it did not function properly. The mixture of charcoal and soda-lime was divided into three separate layers and these separated by cotton pads. The pads offered protection against stannic chloride smokes but not against smokes of the type of sneezing gas. The green soda-lime was replaced by the pink granules. In April, 1918, the mesh of the absorbent was changed to 8 to 14 in place of 6 to 14.

About July 1, 1918, the authorities were convinced by the field forces of the Chemical Warfare Service that the length of life of the chemical protection of the standard _H_ canister (the type then in use) was excessive and that the resistance was much too high. Type _J_ was therefore adopted, July 27, 1918. In this the volume of the absorbent was reduced from 450 cc. to 300 cc. It was packed in two layers, ⅔ in the bottom and ⅓ in the top. One pad was placed between the layers and one on top. This change gave a lowering of the resistance of 27 per cent (to 2.5 inches) at a sacrifice of 50 per cent of the length of life of the canister, but not of protection during the shortened life. Type _L_ differed from this only in having 325 cc. of absorbent, a change made to decrease leakage about the top cotton pad.

[Illustration: FIG. 57.—U. S. Army Canister, Type _J_.]

The following table shows the relative efficiency of various canisters:

-----------------+----------+----------+----------+----------+------ | | U. S., | British, | French, |German | p. p. m. | Type _H_ | S. B. R. | A. R. S. | -----------------+----------+----------+----------+----------+------ Chloropicrin | 1000 | 770 | 17 | 2 | 43 Phosgene | 2500 | 85 | 54 | 5 | 16 Hydrocyanic acid | 500 | 70 | 90 | | 10 Mustard gas | 100 | 1800 | | 35 | 195 -----------------+----------+----------+----------+----------+------

The figures represent time in minutes till the first traces of gas begin to come through.

[Illustration: FIG. 58.—Type _J_ Canister and Contents]

MANUFACTURE

The following description of the manufacture of the gas mask at the Long Island plant is taken from an article by Col. Bradley Dewey[26]:

[Footnote 26: _J. Ind. Eng. Chem._, =11=, 185 (1919).]

“INCOMING INSPECTION—A thorough 100 per cent inspection was made of each part before sending it to the Assembly Department. The inspectors were carefully chosen and were sent to a school for training before they were assigned to this important work. Every feature found to be essential to the manufacture of a perfect gas mask was carefully checked.

“The incoming inspection of the flexible rubber hose leading from the canister to the facepiece can be taken as an illustration. Each piece of hose was given a visual inspection for buckles or blisters in the ends or in the corrugations; for cuts, air pockets, or other defects on the interior; for loose seams where fabric covering was cemented to the rubber tube; for weaving defects in the fabric itself; and for careless application of the cement. Special tests were conducted for flexibility, as a stiff hose would produce a strain on the soldier’s mouth; for permanent set to insure that the hose was properly cured; for the adhesion of the fabric covering to the hose; and for kinking when the hose was doubled on the fingers. Finally each piece was subjected to a test for leaks under water with a pressure of 5 lbs. per sq in.

“Each eyepiece and the three-way metal connection to the facepiece were subjected to a vacuum test for leakage. The delicate exhalation valve was carefully examined for defects which would be liable to cause leakage. Fabric for the facepiece was given a high-tension electrical test on a special machine developed at the plant to overcome the difficulty met in the inspection of this most important material. It was of course necessary that the facepiece fabric be free from defects but just what constituted a defect was the source of much discussion. The electrical test eliminated all personal views and gave an impartial test of the fabric. The machine consisted of two steel rolls between which a potential difference of 4,000 volts was maintained; the fabric was led through the rolls and wherever there was a pinhole or flaw the current arced through and burned a clearly visible hole.

“PRELIMINARY FACEPIECE OPERATIONS—Blanks were died out from the facepiece fabric in hydraulic presses. Each face blank was swabbed to remove bloom and the eye washers were cemented about the eyeholes. The pockets for holding the noseclips were also cemented to the blanks. The bands which formed a gas-tight seal of the mask about the face were died out from rubberized fabric to which a felt backing was attached. The harness consisting of elastic and cotton tapes was also sewed together at this point.

“FACEPIECE OPERATIONS—The sewing machine operations were next performed. First the died out blanks were pleated to form the facepiece. The operator had to register the various notches in the blank to an accuracy of ¹/₃₂ in. and to locate the stitches in some cases as closely as ¹/₆₄ in. The band was next sewed to the periphery of the facepiece after which the harness was attached. The stitches on the outside of the facepiece were covered with liquid dope, which filled the needle holes and made the seams gas-tight.

“In addition to the inspection of each operation, the completed facepiece was submitted to a control inspection to discover any defects that might escape the attention of the inspectors on the various operations.

“ASSEMBLY OPERATIONS—The facepieces were now ready for assembly and were sent for insertion of the eyepieces, which was done in specially designed automatic presses. The eyepieces had to be carefully inserted so that the facepiece fabric extended evenly around the entire circumference.

“Before manufacture began on a large scale, the most satisfactory method of conducting each assembly operation was worked out and the details standardized, so that operators could be quickly and efficiently trained. No detail was considered too small if it improved the quality of the mask. The assembly operations proceeded as follows:

“The exhalation valve was first joined to the three-way metal tube which formed the connection between the facepiece, flexible hose, and mouthpiece. Each valve was then tested for leakage under a pressure difference of a one inch head of water. No valve was accepted which showed leakage in excess of 10 cc. per min. under these conditions.

“The metal guard to protect the exhalation valve was next assembled, followed by the flexible hose. The three-way tube was then assembled to the facepiece by means of a threaded connection and the rubber mouthpiece attached. To illustrate the attention to details the following operation may be cited:

“The contact surfaces between each rubber and metal part were coated with rubber cement before the parts were assembled. The connection was then tightly wired, care being taken that none of the turns of wire should cross and finally the wire was covered with adhesive tape so that no sharp edges would be exposed.

“The masks, completely assembled except for the canisters, were inspected and hung on racks on specially designed trucks which prevented injury in transit, and were delivered to the Finishing Department.

“CANISTER FILLING—Meanwhile the canisters were being filled, in another building.

“The chemicals were first screened in such a way that the fine and coarse materials were separated from the correctly sized materials. They were then carried on a belt conveyor to the storage bins, whence they were fed by gravity through pipes to various mixing machines. A special mixing machine was developed to mix the carbon and granules in the proper proportions for use in the canister. The mixed chemicals were then led to the canister-filling machines. There was a separate mixing machine for each filling machine, of which there were eighteen in all.

“The can-filling department was laid out in six units. Each unit had a capacity of 20,000 cans per day. A system of double belt conveyors was installed to conduct empty canisters to the machines and carry away the filled ones.

“Each filling operation was carefully inspected and special stops were placed on the belt conveyors so that a canister could not go to the next operation without having been inspected. Operators and inspectors were stationed on opposite sides of the belt. The chemicals were placed in the canister in three equal layers which were separated by pads of cotton wadding. The first layer was introduced from the filling machine (which delivered automatically the proper volume of chemicals), the canister was shaken to pack the chemicals tightly, the cotton baffle inserted, the second layer of chemicals introduced and so forth. On top of the top layer of chemicals were placed a wire screen and a specially designed spring which held the contents of the canister securely in place. The metal top was then fitted and securely soldered.

“Each canister was tested under water for possible leaks in joints or soldering, with an air pressure of 5 lbs. per sq. in. A test was also made for the resistance which it offered to breathing, a rate of flow of air through the canister of 85 liters per min. being maintained and the resistance being measured in inches of water.

“The filled canisters were then painted a distinctive color to indicate the type of filling.

“FINISHING DEPARTMENT—In the finishing department, the filled canisters, were conducted down the middle of the finishing tables and assembled to masks.

[Illustration: FIG. 59.]

“The finished masks were then inspected, placed in unit boxes, ten to a box, and returned for the final inspection.

“FINAL INSPECTION—Final inspection of the completely assembled masks was as rigid as could be devised, and was closely supervised by army representatives. Only the most painstaking, and careful women were selected for this work and the masks were examined in every detail to discover any defect that might have escaped previous inspection. Finally, each mask was inspected over a bright light in a dark booth for small pinholes which the ordinary visual inspection might not have detected.

“As a check on the quality on the final inspectors’ work a reinspection of 5 per cent of the passed masks was conducted. Where it was found that a particular inspector was making numerous mistakes, her eyes were examined to see whether it was due to faulty eyesight or careless work. Masks containing known defects were purposely sent to these inspectors to determine whether they were capable of continuing the inspection work. In this way the desired standard was maintained.

“A daily report of the final inspection was sent back to each of the assembly departments involved so that defects might be eliminated immediately and the percentage of rejects kept as low as possible.

“After the final inspection the masks were numbered, packed in knapsacks, and the filled knapsacks placed in packing cases, twenty-four to a case.”

TISSOT MASK

The French, as has already been pointed out, early recognized that certain classes of fighting men, as the artillerymen, needed the maximum of protection with the minimum decrease in efficiency. The result of this was the Tissot Mask. Before the United States entered the war, the British standard box respirator had reached a greater degree of perfection, with far greater ruggedness and portability. It was therefore adopted as the American standard. At the time of the invention of the British box respirator and practically up to the time the United States entered the war, masks were worn only during the sporadic gas attacks then occurring and only for a brief period at a time. As the war progressed, the men were compelled to wear their masks for much longer periods (eight hours was not uncommon). It was then seen that more comfort was needed, even at the expense of a little safety.

The principle of the Tissot mask was correct so far as comfort was concerned, since it did away with the irritating mouthpiece and noseclip, but the chief danger in the French mask arose from the fact that the facepiece was made of thin, pure gum rubber. The Research Division, together with the Gas Defense Division, developed two distinct types of Tissot masks. The first of these was the Akron Tissot, the second the Kops Tissot. The best features of these have been combined in the 1919 Model.

[Illustration: FIG. 60.—American Tissot Mask, Early Type.]

[Illustration: FIG. 61.—American Tissot Mask, Interior View.]

1919 MODEL AMERICAN MASK

=Facepiece.= This facepiece is made of rubberized stockinet about one-tenth inch in thickness. The stockinet is on the outside only and is for the purpose of strengthening and protecting the rubber which is of very high grade. The facepiece is died out as a single flat piece from the stockinet which is furnished in long rolls. The die is of such shape that when the facepiece is sewed there is but one seam, and that between the angle tube opening and the edge under the chin. This seam is sewed with a zigzag stitch with the stockinet sides flat together. The seam is then stretched over a jig, so as to form a flat butt joint. This seam is then cemented with rubber cement and taped, inside and out, to make it thoroughly gas-proof.

The eyepiece openings are of oval shape with the longer axes horizontal and considerably smaller than the finished eyepieces. The eyepieces being circular, the cloth is stretched to accommodate them, giving the necessary bulge to keep the cloth and metal of the eyepieces away from the face. The harness has three straps on each side. Instead of the single strap over the top of the head, two straps lead from directly over the eyes, both being made of elastic the same as the other straps. All six straps are brought together around a pad of felt and cloth about 2½ × 3½ inches at the back of the head. This pad makes the harness much more comfortable.

The rubberized stockinet is reinforced on the inner or rubber side with thin bits of cloth at all points where the straps are sewed on. The strap across the temples just above the ears is sewed at two points, one about one-half inch from the edge and the other about two inches from the edge. This is for the purpose of helping press the cloth against the temples, thereby adding to the gas-tightness for those heads that have a tendency to be hollow at the temples. The lower strap is just above the chin and is for the purpose of giving gas-tightness in that vicinity. All of the straps except the two over the top of the head are attached to the pad with buckles, and are thus capable of exact adjustment.

The eyepieces are of triplex glass in metal rings with rubber gaskets. In pressing the rings home, the rubberized stockinet is turned and held securely so that there is no possibility of pulling them out. The angle tube containing the outlet valve and the connection to the corrugated tube connecting with the canister is the same as with the latest model R. F. K. mask. The only difference as regards the corrugated tube is that a greater length is needed with the new carrier under the left shoulder. The total length of the tube for this model is about 24 inches. On the inside of the facepiece and connected to the angle tube inlet is a butterfly baffle of rubber, so arranged that the incoming air is thrown upward and over the eyepieces, thus keeping them clear no matter how much the exertion or what the temperature, except in certain rare cases when the temperature is down at zero F. or below.

[Illustration: FIG. 62.—1919 Model American Mask.]

CANISTER

The canister is radically different from the canisters used in the R. F. K. and earlier types. In the first place, it is longer, the total length finished being 8 inches. It has two inlet valves at the top end protected by a tin cover instead of the single inlet valve at the bottom of the earlier types. The two inlet valves are each ⅝ inch in diameter and are made up of square flat valves on the end of a short rubber tube. The rubber tube is fitted over a short metal tube. Gas-tightness is obtained both by the pressing of the valve against the round edge of the metal tube and by the pressure of the edges against each other. These valves, while delicate, are proving very satisfactory, and being simply check valves to prevent the air going back through the canister, they are not vital. In case of failure, the eyepieces would fog somewhat and the dead air space be increased by that held in the inlet tube.

The canister consists really of two parts—an outer casing that is solid and an inner perforated tin casing. Around the perforated tin is fitted a filter of wool felt ³/₁₆ of an inch in thickness. This wool felt is very securely fastened by turning operations to solid pieces of tin, top and bottom, so that no air can get into the chemicals without passing through the filter. Thus the air coming through the inlet valves at the top circulates around the loosely fitting outside corrugated case to all parts of the filter and after passing through the filter continues through the perforations of the tin into the charcoal and soda-lime granules.

The chemicals are packed around a central wedge-shaped tube extending about two-thirds the length of the can. The wedge is enlarged at the top and made circular where it passes through the top of the can to connect with the corrugated tube. The wedge-shaped inner piece is made of perforated tin and is covered with thin cloth to prevent dust from the chemicals passing into the tube and thus into the lungs. The cans are filled from the bottom and are subjected to two mechanical jarring operations in order to settle the chemicals thoroughly before the spring which holds them in place is added. The outer tin cap protecting the inlet valves has two openings on each side but none at the ends of the canister.

[Illustration: FIG. 63.—1919 Model American Mask after Adjustment.]

The carrier is a simple canvas case nearly rectangular, about one foot wide and 15 inches in length. The width is just sufficient at the back to hold the canister and the front part to hold the extra length of corrugated tube and the facepiece. There are two straps, one passing over the right shoulder and the other around the body. The one passing over the right shoulder has two “V” shaped seams at the top so as to change the direction of the strap over the shoulder in order that it will pull directly downward instead of against the neck. The flap closing the case opens outward.

It has the usual automobile curtain fasteners. A secondary fastener at the top of the opening is arranged so that when the tube is adjusted to the proper length and the mask is adjusted to the face of the wearer, the flap can be buttoned tightly over the corrugated tube and held tightly. This prevents water from entering the case.

Figures 62 and 63 show the position of the carrier both with the facepiece in the carrier and after adjustment. It will be noted that the carrier does not interfere with the pack nor with anything on the front of the body. The left arm hangs almost entirely natural over the case. It has been thoroughly tried out by the Infantry, Cavalry, Artillery and Special Gas Troops and adopted as eminently satisfactory.

SPECIAL CANISTERS

=Navy.= The early Navy canister is a drum much like the German canister. The container is a slightly tapered metal cylinder, 9 cm. in diameter at the bottom. The most satisfactory filling for this drum consists of two layers, 98 cc. in each, of a standard mixture of charcoal and soda-lime, separated by cotton wadding pad. The filling is 6-20 mesh, instead of 8-14 mesh. A later type is shown in Figure 41.

=Carbon Monoxide.= This canister is discussed in