Not napalm . Napalm is a mixture of Naphthanic & Palmitic acid [hence NAPALM] used to gelatinise petroleum to make a jellied inflammable mixture . This was n't invented until WW2 . The probable filling was Phosphorous . The germans were world leaders in chemistry at the beginning of the 20th century . Text books have said the filling of German incendries was a liquid but this is doubtful .