ref petting Heat or Caloric. 213 



'for any fubftance placed before the cock when it is opened 

 is reduced in temperature. . Water fo placed will even be 

 converted into ice, in confequence of a portion of its heat 

 being violently feized upon by the gas, and more quickly 

 taken into union with it than the privation experienced by 

 the water is compenfaled for by unrounding bodies in the 

 pafiage of caloric from them to reftore the equilibrium. 



I am aware that it may be objected againft this experiment, 

 indeed I have heard the objection offered, that the friction of 

 the forcing fvringe mull excite or accumulate a confiderable 

 portion of heat in the materials of which it is made; that 

 the air, paffing inftantly from it into the condenfing ball, 

 muft neceffarily carry a portion of the heat along with it, 

 having no intermediate bodies to come in contact with ; and 

 that therefore we have no evidence of heat being in this cafe 

 exprefled from the comprerTed air. 



Some force might be allowed to this objection, if the air, 

 when liberated, had no effect in reducing the temperature of 

 the bodies expofed to it; but, as it has the power of taking 

 from them a portion of their heat, and of reducing them below 

 the common temperature, the objection falls to the ground : 

 for, if the heat found to be accumulated in the materials of 

 the condenfing ball was only a confequence of its containing 

 air, made hot by paffing from a cylinder healed by friclion, the 

 air when liberated lhould blow hot, and raife the temperanre 

 of the bodies expofed to the llream inffead of lowering it a as 

 we find it does. The reafoning here is conclunve, but any 

 perfon may alio have the evidence of a direct experiment. 

 JLxpofe the ball of an air-gun, charged only with one atmo- 

 iphcre, to the heat of a common lire till the temperature of 

 the ball be railed a few degrees : the contained air will now 

 be in a lituation to expand itfelf as foon as the valve is 

 opened ; for we know that the air has been heated by the 

 ball. Expofe a thermometer to the aperture as the air efcapes, 

 and the thermometer will indicate an inereafed temperature. 



I have heard fome object to the inference from a con- 

 denfing ball being heated when charged, by queftiofniig the 

 fact for " they have often applied their hand to it without 

 8 perceivjng 



