The Riddle of the Rhine. By Victor Lefebure. Victor Lefebure was a French chemical liason officer during the war; in this book he gives a comprehensive description of the development of chemical warfare, from the first use of gas by the Germans in 1915 to the last campaigns of the war. The account of the change, of the releasing of gas from cylinders, to the use of the “Livens Projector” and the German “cross shells” containing gaseous cornpounds of phosphorus, arsenic and organic poisons, is most interesting