=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.