J50 BULLETIN 173, U. S. NATIONAL MUSEUM 



partly advanced, and the free piston is driven to the top of its stroke. 

 Cooling of the gases then forms a partial vacuum in the cylinder, and 

 the piston, which is now engaged to the motor shaft, is driven down- 

 ward by atmospheric pressure. A slight compression of the gases 

 of combustion at the bottom of the cylinder retards the fall of the 

 piston sufficiently to free it from the motor shaft so that it may be 

 picked up again lightly for the next stroke. A heavy flywheel carries 

 the engine through the cycle. 



Engines of this type consumed 44 cubic feet of Paris gas per indi- 

 cated horsepower hour. The maximum pressure in these engines 

 seldom exceeded 50 pounds per square inch. The great defects of the 

 engine were its noisy and unsteady action and the excessive vibration 

 and recoil. 



See Gas^ Oil and Air Engines^ by Bryan Donkin (London, 1905), 

 for drawings, indicator diagram, and description. 



BRAYTON GAS ENGINE, 1872 



U.S.N.M. no. 251280; original patent model; transferred from the United States 

 Patent Office; not Illustrated. 



This working model was submitted by George B. Brayton, of Bos- 

 ton, Mass., with his application for U. S. Patent no. 125166, dated 

 April 2, 1872. 



The engine was the first to employ the principle of combustion at 

 constant pressure. It also accomplished compression of the explosive 

 mixture before ignition and was one of tlie first gas engines built 

 commercially. See also Brayton Oil Engine, 1874. 



In this engine gas and air were drawn in above the piston, com- 

 pressed in the upper part of the cylinder, and discharged into a re- 

 ceiver under pressure of about 60 pounds per square inch. The ex- 

 plosive mixture entered the lower part of the cylinder through a series 

 of wire gauze diaphragms, which prevented the flame from flashing 

 back to the explosive mixture in the receiver. The mixture was ig- 

 nited just before admission and entered the cylinder in a state of 

 flame and drove the piston forward without any rise in pressure, a 

 steady combustion being maintained behind the piston during one- 

 third of the forward stroke. 



ERRANI AND ANDERS PETROLEUM ENGINE, 1873 



U.S.N.M. no. 251283 ; original patent model ; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with application for Patent no. 140021, 

 issued to Louis Charles Errani and Richard Anders, of Liege, Bel- 

 gium, June 17, 1873. 



This is the first oil engine patented in the United States in which 

 the fuel was vaporized within the cylinder. It is also the first to 



