Page:The New International Encyclopædia 1st ed. v. 18.djvu/632

* STEAM TURBINE. 538 STEARIC ACID. one drum or shaft within a concentric case hav- ing interior blades; the moving vanes or blades ontbe shaft are in circumferential rows project- ing outwardly from the shaft and nearly touch- ing the case, and the fixed blades on the casing are in similar rows, projecting inwardly from the ease and nearly touching the spindle or shaft. This construction constitutes what practically amounts to a series of turbine wheels on one shaft, each one complete in itself, like a parallel flow or Jonval water turbine, through which the steam is forced to pass. Each successive turbine is also slightly larger in passageway than its predecessor, to allow for the increasing bulk of the elastic steam as it exerts its force on each turbine successively and expands with a conse- quent reduction of pressure. The steam in pass- ing through the successive turbines transmits to each a rotative impulse partly by reaction and partly by impulse, and thus the Parsons turbine involves' the germinal principles of both the Branca turbine and Hero's engine. The notable feature of the Parsons turbine is the 'compound- ing' of the steam, or its expansion in successive /Ixis of "W Rotation SECTION OF NOZZLE OF DE LA- VAL'S STEAM TURBINE. Two other turbines which have gained some prominence are the Seger turbine, a Swedish in- vention, which is similar in principle to the De Laval, but which employs two revolving vane wheels, instead of one, upon which the steam acts successively, and the turbine invented by J. H. Dow of Cleveland, O., which is notable as hav- ACTION OF STEAM IN DE LAVAL'S TUKBINE. stages, losing a few pounds in pressure at each stage. This quality of the machine permits a slow enough speed of rotation without serious loss of efficiency to allow the turbine to be coupled direct to a dynamo or even a screw propeller without the necessity of reduction gearing. It has been successfully" employed in both these capacities. The De Laval turbine is simply a highly im- proved form of Branca's impulse turbine. It con- sists of a divergent nozzle which directs the jet of steam upon suitably formed buckets which are attached to the periphery of a revolving wheel. The outer edge of the buckets is shrouded by a steel ring which prevents the centrifugal St-ecrm Chest Nozzle Moving Blades I. ^ ^ ;-.^ i-.','; 1^ ^. '■. -i^^ SmionaryBhdcs ^^^^^SMii<^^M. Moving Blades WM : ' '. -^3M SmionaryBcd^WMLiiiMiMMiSS^ Mcvin^Blades WW'MTJv'FWlWpWWM ACTION OF STEAM BLADES OF CURTIS'S TDRBINE. escape of the steam. These turbines, especially in the larger sizes, are equipped with several nozzles. They are essentially of very high speed, the smaller sizes running at 30,000 revolutions per minute and the larger sizes at 10.000 revo- lutions per minute. A train of gearing reduces the speed to reasonable working velocities. Floor Elevai-ion. Line y/ Plan CURTIS TCIIBINE OPERATING DYNAMO. ing the same principle of 'compounding* the steam as does the Parsons turbine, but which differs materially in construction from the Par- sons machine. STEARIC ACID (from Gk. ar^ap, stenr, tal- low), CjsHjoO,. One of the solid fatty acids. It exists as a glyceride (stearin) in most fats, and is especially abundant in the more solid kinds, such as mutton-suet. Tlie stearic acid of com- merce is in reality a mi.xture of stearic and palmitic acids. Pure stearic acid may readily be separated from this mixture by dissolving in hot alcohol and precipitating with a hot alcoholic solution of magnesium acetate, the precipitate being composed of practically pure stearate of magnesium ; in this reaction, one part, by weight, of magnesium acetate should be employed for everv four parts of commercial stearic acid treated. The magnesium stearate thus obtained is decomposed by boiling with hydrochloric acid, and the stearic acid set free is further purified by recrystallization frnm alcohol. Pure stearic acid is a colorless crvstalline snlistance having neither taste nor odor;' it melts at 00.2° C. (157° F.). It is insoluble in water, on which it floats, but dissolves in alcohol and ether, its solution redden- ing litmus powerfnlly. It may be distilled under diminished pressure. The only stearates soluble in water are the stearates of the alkalies, whose solutions are frothy and form a lather, but on