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Eduard Theisen (1847-1911)
1911 Obituary 
EDUARD THEISEN was born on June 29, 1847, in Schoneberg, near Sinzig on the Rhine. In his early years he went through a course of study at the Agricultural High School at Leipzig, after which he spent several years in America, where American farming on a large scale afforded him ample scope for the practical application of his knowledge of agriculture. His chief interest, however, centred in agricultural machinery, and on his return to Germany in 1873 he directed his efforts to the introduction of steam ploughs, threshing machines, wind turbines, &c., adopting these first on his own estate at Slesin, near Bromberg, and afterwards introducing them on other large estates. Owing to the great advantages resulting from the use of the machines, the demand for them was rapidly increased, and Mr. Theisen was able to establish, first at Bromberg and afterwards at Leipzig, an important agency for agricultural machinery, which became widely celebrated. Mr. Theisen then interested himself in evaporating and drying apparatus for distilleries and breweries, in which branch he was a pioneer and inventor of various apparatus for the purpose referred to. For the manufacture and sale of the Theisen apparatus, the firms of Theisen-Werth & Company, and Theisen & Company were established at Munich and at Hanover, respectively.
His invention of surface condensers, a description of which was published in Stahl and Eisen in 1889, was of the greatest utility to the whole of the engineering industry. On the death of his wife in 1884, he transferred his patents and his Leipzig works, with all the plant, to the firm of Langen in Grevenbroich, which continued to carry on business under the altered name of Theisen & Langen.
After this Mr. Theisen lived for some years in retirement at Radolfszell. His inventive genius, however, would not allow him to remain inactive, and he continued to develop his patents in connection with condensers, in which he effected various essential improvements. He also invented a number of processes and apparatus in connection with the evaporation and concentration of liquids.
In the iron industry both at home and abroad Eduard Theisen enjoyed a wide reputation on account of the well-known pioneer inventions which bear his name. At the time when blast-furnace gas first began to be utilised for the driving of large gas-engines, Mr. Theisen had already taken out patents for rotary gas-cleaning apparatus, in which a high degree of efficiency was attained in the purifying of all kinds of fuel gases. Notwithstanding the difficulties which were at first encountered in the successful removal of dust from gases, the Theisen centrifugal counter-current gas-washer proved an effective means for overcoming these, and its usefulness may be judged from the fact that it is now installed in almost every ironworks.
From 1893 to 1903 Mr. Theisen maintained a consulting engineer's office at Baden-Baden. In the latter year he transferred his office and his residence to Munich, but latterly he relinquished the conduct of affairs to his son, who still continues to carry on the business.
Mr. Theisen was elected a member of the Iron and Steel Institute in 1901.