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 Chapter XI.