Phosgene Introduced
The use of chlorine alone continued until the introduction on December 19, 1915, of a mixture of phosgene with the chlorine. This mixture offered many advantages over the use of chlorine alone ([see Chapter VI]).
The Allies were able, through warning of the impending use of phosgene, to furnish a means of protection against it. It was at this time that the P and the PH helmets were devised, the cotton filling being impregnated with sodium phenolate and later with a mixture of sodium phenolate and hexamethylenetetramine. This helmet was used until the Standard Box Respirator was developed by the late Lt. Col. Harrison.