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.