132 BULLETIN 173, U. S. NATIONAL MUSEUM 



independently of each other. The quantity of air contained within 

 the cylinder is used repeatedly. 



At the beginning of the cycle of operation the work piston is at 

 the bottom of its stroke, and the transfer piston is near the top of 

 its stroke, having displaced the air to the bottom of the cylinder. 

 The air absorbs heat from the furnace walls and expands, perform- 

 ing work as it forces the work piston to the top of its stroke. The 

 transfer piston in the meantime travels to the bottom of the cylinder 

 and displaces the air to the top where it gives up heat to the water- 

 jacketed surface and contracts. Atmospheric pressure then forces 

 the work piston down to the bottom of its stroke as the transfer 

 piston rises and displaces the air to the heated lower part of the 

 cylinder, completing the cycle. 



AIPw-AND-STEAM ("AERATOR") ENGINES 



A class of engines known as aerosteam engines, using the expan- 

 sive power of a mixture of heated air and steam and supposed to 

 attain the better features of both air and steam engines, engaged the 

 attention of many inventors during the nineteenth century. Oliver 

 Evans (c. 1790) suggested a "volcanic engine" in which the gases 

 from the furnace were mixed with the steam going to the engine. 

 The hot-air engine of Glazebrook, mentioned above, used moistened 

 air to reduce abrasion of the sliding surfaces. Bennet (1838), Wil- 

 liam Storm (1851-5), Washburn (1865), and Tarr (1867) made aero- 

 steam engines of various types. 



WHITING AEROSTEAM ENGINE, 1879 



U.S.N.M. CO. 251285 ; original patent model ; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with its application for Patent no. 

 217758, issued to James M. AVliiting, of Providence, R, I., July 22, 

 1879. 



This is an example of combined air and steam engines, many de- 

 signs of which have been proposed and built. In this engine the use 

 of steam is intended to reduce the bulk of the heated air required to 

 operate an engine of a given capacity and consequently reduce the 

 size of the engine. 



The model shows a vertical fire-tube steam boiler of ordinary con- 

 struction above the tubes of which is placed a hollow drum that is 

 heated by the hot gases from the boiler. There is also a small steam 

 pump and a vertical high-speed steam engine of the slide-valve type. 

 Steam from the boiler is mixed with the heated air in the upper 

 drum, and the mixture of heated air and steam is led directly to the 

 engine and expanded. The air pump supplies air to the heated drum. 



