I. Low Pressure Compressors.
C. Compressors without Pistons.
2. Steam Apparatus. Injectors. (See also same general heading.)-Mr. Siemens has investigated the application of the steam-injector to the propulsion of gases, and he has constructed an injector which, with steam at 45 lbs. pressure, produces a vacuum of 23.7 inches of mercury.
Fig. 140 is a section of the apparatus. The injection-pipe is slightly conical in form, maintaining the convergences of the concentric air and steam jets toward the axis of the tube on a length compressed between twelve and twenty times the breadth of the annular air-induction aperture. The object of this convergence is to secure complete mingling of steam and air. Mr. Siemens has applied this apparatus to the production of a vacuum in 21,369 feet of pneumatic-dispatch tubes in London. Three injectors maintained in pipes of the above length and 2.9 inches in diameter a vacuum of 9.8 inches of mercury, with steam at a ressure of 29 lbs. per square inch and a consum on of coal of about 56 lbs. per hour. The same apparatus has been used for blast in the Siemens furnace and in sugar-works. It cannot be practically employed as a rule to effect compressions over 25.5 inches of mercury.
3. Apparatus has been produced wherein compressed air
itself has entrained the surrounding atmosphere. Experiment on
this subject has not resulted In the invention of any practicable
machine based thereon.