An Interesting 1931 Airmail Envelope Sent from Braunschweig (Germany) to Peiping (China)

This is an interesting airmail envelope that was sent from Mr. Walter Behrens, from Braunschweig (Germany) of the Behren’s Neuheiten-Dienst, to the District Accountant of the Head Post Office in Peiping (China). It features three German stamps; 1) A 1 Reichsmark Deutsche Luftpost Zeppelin stamp. 2) A 15 Pfennig Deutsche Luftpost Stamp, and a 3) 10 Pfennig Deutsche Luftpost stamp - with all three stamps featuring validation stamps in black ink, dated “Berlin - 16.6.31. 17-18”. The obverse of the envelope is inscribed with “From Berlin to Peiping (China). Via Moskay - Irkutsk with the train to Mandschuli, with airmail via Linsi to Peiping (China)”. The reverse features two stamps from the Peiping postal office. The envelope measures 162 mm x 115 mm. The envelope contains a small piece of paper depicting a map of the world. Overall extremely fine condition.