The early gas bags for the Zeppelins were made of rubberized cotton fabric. This material was comparatively heavy and further, it allowed the hydrogen gas to deteriorate during prolonged operations. Count Zeppelin experimented with various materials, particularly goldbeater skins, which are the big intestines of oxen and other cattle, treated until they become like leather and then they are very thin, tough and so durable that they wear much longer than fabric. Zeppelin learned that goldbeater’s skins held gas better, also, and unlike rubberized fabric, practically eliminated the danger of electrical sparks due to friction or tearing. He organized the Gasbag Manufacturing Company (Ballon-Hüllen G.M.B.H.) at Tempelhof in 1912, to carry out this development and goldbeater’s skins were used exclusively, as the loss of two Zeppelins that year was traced directly to the balloon fabric in the gas bags causing sparks which exploded the hydrogen. The ships were the LZ-12 and the Schwaben, the former exploding during inflation and the latter while moored at Dusseldorf. [PLATE 36: “DELAG”—Zeppelin Harbors at Liegnitz and Dresden, 1913-14. “DELAG”—Zeppelin Harbor and Manufacturing Plant at Potsdam (near Berlin), 1915.] The goldbeater skins possessed certain disadvantages, however. For one thing, they were difficult to handle because of their small size; so they were shingled on to thin cotton fabric. Since 1917 silk has been used, the combination when prepared being so light and thin as to be transparent. In fact, the Zeppelins hulls are themselves nearly transparent, the fabric envelope and gas bags being so thin that one can make out figures silhouetted on the opposite side of the hull when it faces the light. The Tempelhof factory, with Mr. Trenkmann as Manager, now includes many buildings and workshops, several put up recently for dyeing and treating fabrics. During the war a thousand persons were employed. The gas bags used in all the German airships were made there; and the factory working with another firm under a patent license agreement, made a majority of the German observation balloons. The Maag-Zeppelin Gear Works It was not long after the war started that Count Zeppelin had difficulty in securing delivery of cog-wheels, etc. In 1915 he co-operated with Mr. Maag, a Swiss engineer, in starting the Friedrichshafen Cog-wheel and Gear Factory (Zahnradfabrik Friedrichshafen G.M.B.H.), another subsidiary (Plate 18.). The plant is as modern as they could make it. The buildings occupy three acres. They include office buildings, workshops for hobbing, heat-treating, grinding and polishing cog-wheels and the complete gear transmissions. Aluminum castings are obtained from the foundry of the parent company, Luftschiffbau-Zeppelin.