in different forms of the Air-E’ngine. 175 
ling pressure, and the working cylinder might 
be kept absolutely cold. Let abed, for 
lustance, be a cylinder, in which moves the 
piston, P. Let this eylinder communicate 
with the larger one ABCD, closed at top, 
ut communicating with an ait heater, by 
the valve E. ABCD being filled with a 
liquid, and also abcd, up to the working piston, air may be ad- 
iuitted to the first, which will transmit its pressure through the 
liquid to the piston. A valve, F', may then discharge the air. 
ay keeping the bottoms of the vessels, and the connecting chan- 


known liquid, however, would answer this purpose, unless it 
should be oil; and that would not answer at the high tempera- 
‘ures which have been proposed. | ; 
ethaps the idea is not entirely absurd of filling the chamber 
ABCD with the fusible alloy of lead, tin and bismuth, which 
liquefies at about 212° F. The high specific gravity would 
render great change of level undesirable, and hence ABCD 
might bear a large ratio in cross section to abed; while the lat- 
‘et cylinder might still contain oil, and the alloy might be chiefly 
*onfined to ABCD and the communicating passage.* By this 
Means the temperature of the working cylinder might be kept 
lower than that of a high pressure steam engine. The tendency 
of the alloy to oxydize would be an evil which would require to 
* Below the range of the piston, however, abcd should be equal to ABCD. 
