*There were 2 different types of filters for the gummimaske, filter type 1915 and filter type 11/11.  Filter type 1915 contains diatomite impregnated with a 40% solution of potash, powdered over with active carbon.  Filter type 11/11 contains 3 layers. The top layer contains diatomite impregnated with potash solution, piperazine and hexamethylenetetramine. The middle layer contains active carbon. The bottom layer contains the  same mixture used in filter type 1915.