IQQ BULLETIN 173, U. S. NATIONAL MUSEUM 



It was then apparent that the usefiihiess of the engine would be 

 greatly increased if it did not depend upon a connection to a gas- 

 manufacturing plant for its fuel. Combustible liquids such as tur- 

 pentine, alcohol, and petroleum were used in the earliest engines by 

 heating the liquid fuel in separate retorts or within the cylinders 

 of the engines and mixing the evaporated vapor with air to form 

 combustible mixtures. Also, several early engines had atomizers 

 and oil "pulverizers", which operated under pressure from fuel 

 pumps to spray finely divided oil into the air before or after it 

 entered the cylinder. However, the internal-combustion engine did 

 not cease to be the gas engine until the invention of carbureting 

 devices that formed combustible mixtures from liquid fuels through 

 the action of the suction stroke of the engine alone. Carburetors 

 in this sense have been historically of three classes, surface carbu- 

 retors, mixing valves, and spray carburetors. 



Surface carburetors are essentially mixing chambers in which a 

 quantity of the liquid fuel is so contained that air drawn through 

 the chamber passes over the largest possible surface of the fuel, 

 to become saturated or carbureted with the vapor of the fuel. In 

 the earliest ones the fuel was held in shallow trays or allowed to 

 run over metal screens to obtain the necessary surface area of liquid. 

 They were at first large clumsy tanks, often installed underground, 

 and, though they permitted the gas engine to be used where gas 

 was not available, they did not add much to the portability of the 

 engine. Later surface carburetors were made with such porous 

 materials as wood, wicking, and gauze in place of the trays or 

 screens, with the result that when the absorbent material was wetted 

 with fuel a much larger total surface of liquid was obtained in a 

 smaller space. The Manly carburetor, described below, is an example 

 of the use of wood for this purpose. An English automobile was 

 equipped with a surface carburetor in which cotton wicking v/as 

 used, as late as 1911. The first small and portable carburetors were 

 the surface carburetors of Daimler and Benz in which the air was 

 drawn across the surface of the fuel through a diffuser floating upon 

 the surface. These carburetors made the internal combustion engine 

 portable and made possible the early development of the gasoline 

 automobile. However, they lacked the flexibility necessary to sup- 

 ply correct mixtures at varying speeds and temperatures and fre- 

 quently removed the lighter constituents from the fuel leaving be- 

 hind the heavier liquids, which in time clogged the surfaces. Surface 

 carburetors were generally superseded by inixing valves. 



The usual form of the mixing valve was a flat conical valve, the 

 tip of which shut off the fuel supply at the same time that the body 

 of the valve closed the air intake passage. The valve was closed 

 by a light spring and was opened b}^ the partial vacuum created by 



