W.G. Thayer. "Learn to Adjust Your Respirator." 1915. Lithograph poster in color. Issued by the Chemical Warfare Service. Instructional poster for gas mask safety issued to soldiers and posted in mask factories to encourage flawless production. Sheet: 29 1/4" x 20".Condition Very good +. Foldmarks, losses to upper and lower left corners, closed tears to top margin, some small open tears to image where foldmarks meet.