It was evident that the metal tube passing through the face piece must not contain pinholes and must be able to stand rough handling without pulling loose. The harness must maintain a gas-tight connection between the wearer's face and the face piece, but not at the cost of pain or chafing of the face or head. The flutter valve must fit with absolute tightness and must work perfectly and instantaneously at all times.
The flexible hose leading from the canister to the face piece must be strong and without flaws or leaks, and yet flexible in the extreme. A stiff hose would be likely to swing and displace the face piece whenever the wearer moved. The mouthpiece must be comfortable and must be built along lines to prevent irritation to the gums or lips, yet it must be reinforced so that in his excitement the soldier can not bite down and shut off his air supply.
The canister must withstand corrosion and must be gas-tight. Smooth sided canisters can not be used, for the gas would slip up the sides without coming in contact with much of the chemical filling. The sides of the canisters were, therefore, ribbed so that the charcoal and other ingredients working into these ribs baffled the gas and threw it out into the body of the chemicals. The canister, moreover, must be equipped with a perfectly working check valve which will stop exhalation through the canister and force the air to pass out through the flutter valve.
The web sling of the knapsack must not curl and chafe the neck or shoulders of the wearer. The knapsack must be waterproof and must have easily and quickly workable fastenings.
The canisters were filled with charcoal and with cement granules. These were crushed into carefully sized small bits about the size of a pinhead and packed in layers in the canisters. The air could pass through them easily and the particles of both substances absorbed gas. The chief quality requirements for the carbon and the cement were that they must have long life and great activity.
Of the canister ingredients the charcoal offered the more difficult technical problem. It had long been known that charcoal was highly absorptive of certain gases, but except in rare instances no thorough study had ever been made of the subject. It was evident, however, that the more charcoal or carbon which could be packed into the canister and still allow the free passage of air the greater the amount of gas that would be absorbed. Consequently a search was made for carbon existing in the natural state in the most compact form. This search is described later.
Each canister also contained concrete granules in a definite proportion to the carbon pieces. These granules were made of cement mixed with strong alkalis and oxidizing agents to digest the poisons as they passed through the canister.
It will be seen that the manufacture of good gas masks was a highly technical undertaking, one calling for the best talents of eminent men of science. The mask was not something that could be improvised on the spur of the moment, but each part of it must be worked out after the most painstaking research. The Gas Defense Division of the Chemical Warfare Service never at any time approved a type of mask which its own officers or men did not themselves wear in the most deadly concentrations of gas.
To get back to the chronological order of development, on May 21, 1917, the making of the first 25,000 masks was started with frantic haste; though, as it developed later, there was no need for such an effort, since there were available in England and France plenty of masks for the first American troops. Working to produce in the shortest possible time some sort of protection for the first overseas division, the officers in charge were forced to adopt methods which, had they been followed throughout the manufacturing program, would have been extremely costly. There was no time then to stop and study the problem either here or abroad. Before the end of June 20,088 masks had been started overseas, and 5,000 more were ready a little later. The most that can be said for this effort was that it gave our officers the experience which was the groundwork of the solid development later on.
The production of these first 25,000 masks called upon the services of various manufacturers. The assembling of the masks was conducted by the American Can Co., at Brooklyn, N. Y. The B. F. Goodrich Co., of Akron, manufactured the face pieces with the eyepieces inserted, also the connecting hose, the check valve of the canister, the flutter valve, and the rubber mouthpiece. The American Can Co. produced the canisters. The Day Chemical Co., of Westline, Pa., gave the charcoal its first burning. The Ward Baking Co., of Brooklyn, patriotically baked the charcoal—to activate it—in their bread ovens free of charge. The General Chemical Co., of New York, supplied the soda-lime granules. The Doehler Die Casting Co., of Brooklyn, manufactured the angle tubes. The Simmons Hardware Co., of St. Louis, produced the waterproof knapsacks. The Seaver Howland Press, of Boston, printed the cards of instructions that went with the mask outfit; and the Beetle & MacLean Manufacturing Co., of Boston, printed the record tags.