The earliest protection against gas was the crudest sort of a mask. The first gas used was chlorine and since thousands of people in civil life were used to handling it, many knew that certain solutions, as hyposulfite of soda, would readily destroy it. They also knew that if the breath could be drawn through material saturated with those solutions, the chlorine would be destroyed. Thus it was that the first masks were simple cotton, or cotton waste pads, which were dipped into hyposulfite of soda solutions and applied to the mouth and nose during a gas attack. These pads were awkward, unsanitary, and, due to the long intervals between gas attacks, were frequently lost, while the solution itself was often spilled or evaporated. The net result of all this was poor protection and disgust with the so-called masks. DESIGN OF NEW MASKS After using these, or similar poor excuses for a mask, for a few weeks, the British designed what was known as the PH helmet. In a gas attack the sack was pulled over the head and tucked under the blouse around the neck, the gas-tight fit being obtained by buttoning the blouse over the ends of the sack. This PH helmet was quite successful against chlorine and, to a much less extent, against phosgene, a new gas introduced during the spring of 1916. But it was warm and stuffy in summer—the very time when gas is used to the greatest extent—while the chemicals in the cloth irritated the face and eyes, especially when combined with some of the poisonous gases. Probably as a result of experience with oxygen apparatus in mine rescue work, Colonel Harrison suggested making a mask of which the principal part was a box filled with chemicals and carried on the chest. A flexible tube connected the box with a mouthpiece of rubber. Breathing was thus through the mouth and in order to insure that no air would be breathed in through the nose, a noseclip was added. This, of course, cared for the lungs, but did not protect the eyes. Their protection was secured by making a facepiece of rubberized cloth with elastics to hold it tight against the face. The efficiency of this mask depends, then, first upon the ability of the facepiece to keep out lachrymatory gases which affect the eyes, and, second, upon a proper combination of chemicals in the box, to purify the air drawn into the lungs through the mouthpiece. (Details are given in Chapter XII). PROTECTION AGAINST SMOKE